GNU Emacs Manual

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The Emacs Editor

Emacs is the extensible, customizable, self-documenting real-time display editor. This Info file describes how to edit with Emacs and some of how to customize it; it corresponds to GNU Emacs version 22.0.50.

For information on extending Emacs, see Emacs Lisp.

Indexes (nodes containing large menus)

Important General Concepts

Fundamental Editing Commands

Important Text-Changing Commands

Major Structures of Emacs

Advanced Features

Recovery from Problems

Detailed Node Listing ---------------------

Here are some other nodes which are really inferiors of the ones already listed, mentioned here so you can get to them in one step:

The Organization of the Screen

Basic Editing Commands

The Minibuffer


The Mark and the Region

Killing and Moving Text



Controlling the Display

Searching and Replacement

Replacement Commands

Commands for Fixing Typos

Keyboard Macros

File Handling

Saving Files

Version Control

Using Multiple Buffers

Multiple Windows

Frames and X Windows

International Character Set Support

Major Modes


Commands for Human Languages

Filling Text

Editing Programs

Top-Level Definitions, or Defuns

Indentation for Programs

Commands for Editing with Parentheses

Manipulating Comments

Documentation Lookup

C and Related Modes

Fortran Mode

Compiling and Testing Programs

Running Debuggers Under Emacs

Maintaining Programs

Tags Tables

Merging Files with Emerge


Editing Pictures

Sending Mail

Reading Mail with Rmail

Dired, the Directory Editor

The Calendar and the Diary

Movement in the Calendar

Conversion To and From Other Calendars

The Diary


Running Shell Commands from Emacs

Using Emacs as a Server

Hyperlinking and Navigation Features



Customizing Key Bindings

The Init File, ~/.emacs

Dealing with Emacs Trouble

Reporting Bugs

Command Line Arguments for Emacs Invocation

Environment Variables

X Options and Resources

Emacs and Mac OS

MS-DOS and Windows 95/98/NT

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GNU Emacs is free software; this means that everyone is free to use it and free to redistribute it on certain conditions. GNU Emacs is not in the public domain; it is copyrighted and there are restrictions on its distribution, but these restrictions are designed to permit everything that a good cooperating citizen would want to do. What is not allowed is to try to prevent others from further sharing any version of GNU Emacs that they might get from you. The precise conditions are found in the GNU General Public License that comes with Emacs and also appears in this manual1. See Copying.

One way to get a copy of GNU Emacs is from someone else who has it. You need not ask for our permission to do so, or tell any one else; just copy it. If you have access to the Internet, you can get the latest distribution version of GNU Emacs by anonymous FTP; see on our website for more information.

You may also receive GNU Emacs when you buy a computer. Computer manufacturers are free to distribute copies on the same terms that apply to everyone else. These terms require them to give you the full sources, including whatever changes they may have made, and to permit you to redistribute the GNU Emacs received from them under the usual terms of the General Public License. In other words, the program must be free for you when you get it, not just free for the manufacturer.

You can also order copies of GNU Emacs from the Free Software Foundation. This is a convenient and reliable way to get a copy; it is also a good way to help fund our work. We also sell hardcopy versions of this manual and An Introduction to Programming in Emacs Lisp, by Robert J. Chassell. You can find an order form on our web site at For further information, write to

     Free Software Foundation
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The income from distribution fees goes to support the foundation's purpose: the development of new free software, and improvements to our existing programs including GNU Emacs.

If you find GNU Emacs useful, please send a donation to the Free Software Foundation to support our work. Donations to the Free Software Foundation are tax deductible in the US. If you use GNU Emacs at your workplace, please suggest that the company make a donation. If company policy is unsympathetic to the idea of donating to charity, you might instead suggest ordering a CD-ROM from the Foundation occasionally, or subscribing to periodic updates.

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You are reading about GNU Emacs, the GNU incarnation of the advanced, self-documenting, customizable, extensible real-time display editor Emacs. (The `G' in `GNU' is not silent.)

We say that Emacs is a display editor because normally the text being edited is visible on the screen and is updated automatically as you type your commands. See Display.

We call it a real-time editor because the display is updated very frequently, usually after each character or pair of characters you type. This minimizes the amount of information you must keep in your head as you edit. See Real-time.

We call Emacs advanced because it provides facilities that go beyond simple insertion and deletion: controlling subprocesses; automatic indentation of programs; viewing two or more files at once; editing formatted text; and dealing in terms of characters, words, lines, sentences, paragraphs, and pages, as well as expressions and comments in several different programming languages.

Self-documenting means that at any time you can type a special character, Control-h, to find out what your options are. You can also use it to find out what any command does, or to find all the commands that pertain to a topic. See Help.

Customizable means that you can change the definitions of Emacs commands in little ways. For example, if you use a programming language in which comments start with ‘<**’ and end with ‘**>’, you can tell the Emacs comment manipulation commands to use those strings (see Comments). Another sort of customization is rearrangement of the command set. For example, if you prefer the four basic cursor motion commands (up, down, left and right) on keys in a diamond pattern on the keyboard, you can rebind the keys that way. See Customization.

Extensible means that you can go beyond simple customization and write entirely new commands, programs in the Lisp language to be run by Emacs's own Lisp interpreter. Emacs is an “on-line extensible” system, which means that it is divided into many functions that call each other, any of which can be redefined in the middle of an editing session. Almost any part of Emacs can be replaced without making a separate copy of all of Emacs. Most of the editing commands of Emacs are written in Lisp; the few exceptions could have been written in Lisp but are written in C for efficiency. Although only a programmer can write an extension, anybody can use it afterward. See Emacs Lisp Intro, if you want to learn Emacs Lisp programming.

When run under the X Window System, Emacs provides its own menus and convenient bindings to mouse buttons. But Emacs can provide many of the benefits of a window system on a text-only terminal. For instance, you can look at or edit several files at once, move text between files, and edit files while running shell commands.

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1 The Organization of the Screen

On a text-only terminal, the Emacs display occupies the whole screen. On the X Window System, Emacs creates its own X windows to use. We use the term frame to mean an entire text-only screen or an entire X window used by Emacs. Emacs uses both kinds of frames in the same way to display your editing. Emacs normally starts out with just one frame, but you can create additional frames if you wish. See Frames.

When you start Emacs, the entire frame except for the top and bottom is devoted to the text you are editing. This area is called the window. At the top there is normally a menu bar where you can access a series of menus; then there may be a tool bar, a row of icons that perform editing commands if you click on them. Below this, the window begins. The last line is a special echo area or minibuffer window, where prompts appear and where you enter information when Emacs asks for it. See below for more information about these special lines.

You can subdivide the large text window horizontally or vertically into multiple text windows, each of which can be used for a different file (see Windows). In this manual, the word “window” always refers to the subdivisions of a frame within Emacs.

At any time, one window is the selected window. On graphical terminals, the selected window normally shows a more prominent cursor (solid and blinking) while other windows show a weaker cursor (such as a hollow box). On text terminals, which have just one cursor, that cursor appears in the selected window.

Most Emacs commands implicitly apply to the text in the selected window (though mouse commands generally operate on whatever window you click them in, whether selected or not). The other windows display text for reference only, unless/until you select them. If you use multiple frames under the X Window System, then giving the input focus to a particular frame selects a window in that frame.

Each window's last line is a mode line, which describes what is going on in that window. It appears in different color and/or a “3D” box, if the terminal supports that; its contents normally begin with ‘--:--  *scratch* when Emacs starts. The mode line displays status information such as what buffer is being displayed above it in the window, what major and minor modes are in use, and whether the buffer contains unsaved changes.

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1.1 Point

Within Emacs, the active cursor shows the location at which editing commands will take effect. This location is called point. Many Emacs commands move point through the text, so that you can edit at different places in it. You can also place point by clicking mouse button 1.

While the cursor appears to point at a character, you should think of point as between two characters; it points before the character that appears under the cursor. For example, if your text looks like ‘frob’ with the cursor over the ‘b’, then point is between the ‘o’ and the ‘b’. If you insert the character ‘!’ at that position, the result is ‘fro!b’, with point between the ‘!’ and the ‘b’. Thus, the cursor remains over the ‘b’, as before.

Sometimes people speak of “the cursor” when they mean “point,” or speak of commands that move point as “cursor motion” commands.

If you are editing several files in Emacs, each in its own buffer, each buffer has its own point location. A buffer that is not currently displayed remembers its point location in case you display it again later. When Emacs displays multiple windows, each window has its own point location. If the same buffer appears in more than one window, each window has its own position for point in that buffer, and (when possible) its own cursor.

A text-only terminal has just one cursor, so Emacs puts it in the selected window. The other windows do not show a cursor, even though they do have a location of point. When Emacs updates the screen on a text-only terminal, it has to put the cursor temporarily at the place the output goes. This doesn't mean point is there, though. Once display updating finishes, Emacs puts the cursor where point is.

On graphical terminals, Emacs shows a cursor in each window; the selected window's cursor is solid and blinking, and the other cursors are just hollow. Thus, the most prominent cursor always shows you the selected window, on all kinds of terminals.

See Cursor Display, for customizable variables that control display of the cursor or cursors.

The term “point” comes from the character ‘.’, which was the command in TECO (the language in which the original Emacs was written) for accessing the value now called “point.”

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1.2 The Echo Area

The line at the bottom of the frame (below the mode line) is the echo area. It is used to display small amounts of text for various purposes.

Echoing means displaying the characters that you type. At the command line, the operating system normally echoes all your input. Emacs handles echoing differently.

Single-character commands do not echo in Emacs, and multi-character commands echo only if you pause while typing them. As soon as you pause for more than a second in the middle of a command, Emacs echoes all the characters of the command so far. This is to prompt you for the rest of the command. Once echoing has started, the rest of the command echoes immediately as you type it. This behavior is designed to give confident users fast response, while giving hesitant users maximum feedback. You can change this behavior by setting a variable (see Display Custom).

If a command cannot be executed, it may display an error message in the echo area. Error messages are accompanied by beeping or by flashing the screen. The error also discards any input you have typed ahead.

Some commands display informative messages in the echo area. These messages look much like error messages, but they are not announced with a beep and do not throw away input. Sometimes the message tells you what the command has done, when this is not obvious from looking at the text being edited. Sometimes the sole purpose of a command is to show you a message giving you specific information—for example, C-x = (hold down <CTRL> and type x, then let go of <CTRL> and type =) displays a message describing the character position of point in the text and its current column in the window. Commands that take a long time often display messages ending in ‘...’ while they are working, and add ‘done’ at the end when they are finished.

Echo-area informative messages are saved in an editor buffer named ‘*Messages*’. (We have not explained buffers yet; see Buffers, for more information about them.) If you miss a message that appears briefly on the screen, you can switch to the ‘*Messages*’ buffer to see it again. (Successive progress messages are often collapsed into one in that buffer.)

The size of ‘*Messages*’ is limited to a certain number of lines. The variable message-log-max specifies how many lines. Once the buffer has that many lines, each line added at the end deletes one line from the beginning. See Variables, for how to set variables such as message-log-max.

The echo area is also used to display the minibuffer, a window that is used for reading arguments to commands, such as the name of a file to be edited. When the minibuffer is in use, the echo area begins with a prompt string that usually ends with a colon; also, the cursor appears in that line because it is the selected window. You can always get out of the minibuffer by typing C-g. See Minibuffer.

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1.3 The Mode Line

Each text window's last line is a mode line, which describes what is going on in that window. When there is only one text window, the mode line appears right above the echo area; it is the next-to-last line in the frame. The mode line starts and ends with dashes. On a text-mode display, the mode line is in inverse video if the terminal supports that; on a graphics display, the mode line has a 3D box appearance to help it stand out. The mode line of the selected window has a slightly different appearance than those of other windows; see Optional Mode Line, for more about this.

Normally, the mode line looks like this:

     -cs:ch  buf      pos line   (major minor)------

This gives information about the buffer being displayed in the window: the buffer's name, what major and minor modes are in use, whether the buffer's text has been changed, and how far down the buffer you are currently looking.

ch contains two stars ‘**’ if the text in the buffer has been edited (the buffer is “modified”), or ‘--’ if the buffer has not been edited. For a read-only buffer, it is ‘%*’ if the buffer is modified, and ‘%%’ otherwise.

buf is the name of the window's buffer. In most cases this is the same as the name of a file you are editing. See Buffers.

The buffer displayed in the selected window (the window that the cursor is in) is also Emacs's current buffer, the one that editing takes place in. When we speak of what some command does to “the buffer,” we are talking about the current buffer.

pos tells you whether there is additional text above the top of the window, or below the bottom. If your buffer is small and it is all visible in the window, pos is ‘All’. Otherwise, it is ‘Top’ if you are looking at the beginning of the buffer, ‘Bot’ if you are looking at the end of the buffer, or ‘nn%’, where nn is the percentage of the buffer above the top of the window. With Size Indication mode, you can display the size of the buffer as well. See Optional Mode Line.

line is ‘L’ followed by the current line number of point. This is present when Line Number mode is enabled (which it normally is). You can optionally display the current column number too, by turning on Column Number mode (which is not enabled by default because it is somewhat slower). See Optional Mode Line.

major is the name of the major mode in effect in the buffer. At any time, each buffer is in one and only one of the possible major modes. The major modes available include Fundamental mode (the least specialized), Text mode, Lisp mode, C mode, Texinfo mode, and many others. See Major Modes, for details of how the modes differ and how to select one.

Some major modes display additional information after the major mode name. For example, Rmail buffers display the current message number and the total number of messages. Compilation buffers and Shell buffers display the status of the subprocess.

minor is a list of some of the minor modes that are turned on at the moment in the window's chosen buffer. For example, ‘Fill’ means that Auto Fill mode is on. ‘Abbrev’ means that Word Abbrev mode is on. ‘Ovwrt’ means that Overwrite mode is on. See Minor Modes, for more information. ‘Narrow’ means that the buffer being displayed has editing restricted to only a portion of its text. This is not really a minor mode, but is like one. See Narrowing. ‘Def’ means that a keyboard macro is being defined. See Keyboard Macros.

In addition, if Emacs is currently inside a recursive editing level, square brackets (‘[...]’) appear around the parentheses that surround the modes. If Emacs is in one recursive editing level within another, double square brackets appear, and so on. Since recursive editing levels affect Emacs globally, not just one buffer, the square brackets appear in every window's mode line or not in any of them. See Recursive Edit.

Non-windowing terminals can only show a single Emacs frame at a time (see Frames). On such terminals, the mode line displays the name of the selected frame, after ch. The initial frame's name is ‘F1’.

cs states the coding system used for the file you are editing. A dash indicates the default state of affairs: no code conversion, except for end-of-line translation if the file contents call for that. ‘=’ means no conversion whatsoever. Nontrivial code conversions are represented by various letters—for example, ‘1’ refers to ISO Latin-1. See Coding Systems, for more information. If you are using an input method, a string of the form ‘i>’ is added to the beginning of cs; i identifies the input method. (Some input methods show ‘+’ or ‘@’ instead of ‘>’.) See Input Methods.

When you are using a character-only terminal (not a window system), cs uses three characters to describe, respectively, the coding system for keyboard input, the coding system for terminal output, and the coding system used for the file you are editing.

When multibyte characters are not enabled, cs does not appear at all. See Enabling Multibyte.

The colon after cs can change to another string in certain circumstances. Emacs uses newline characters to separate lines in the buffer. Some files use different conventions for separating lines: either carriage-return linefeed (the MS-DOS convention) or just carriage-return (the Macintosh convention). If the buffer's file uses carriage-return linefeed, the colon changes to either a backslash (‘\’) or ‘(DOS)’, depending on the operating system. If the file uses just carriage-return, the colon indicator changes to either a forward slash (‘/’) or ‘(Mac)’. On some systems, Emacs displays ‘(Unix)’ instead of the colon even for files that use newline to separate lines.

You can customize the mode line display for each of the end-of-line formats by setting each of the variables eol-mnemonic-unix, eol-mnemonic-dos, eol-mnemonic-mac, and eol-mnemonic-undecided to any string you find appropriate. See Variables, for an explanation of how to set variables.

See Optional Mode Line, for features that add other handy information to the mode line, such as the size of the buffer, the current column number of point, the current time, and whether new mail for you has arrived.

The mode line is mouse-sensitive; when you move the mouse across various parts of it, Emacs displays help text to say what a click in that place will do. See Mode Line Mouse.

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1.4 The Menu Bar

Each Emacs frame normally has a menu bar at the top which you can use to perform certain common operations. There's no need to list them here, as you can more easily see for yourself.

When you are using a window system, you can use the mouse to choose a command from the menu bar. An arrow pointing right, after the menu item, indicates that the item leads to a subsidiary menu; ‘...’ at the end means that the command will read arguments (further input from you) before it actually does anything.

To view the full command name and documentation for a menu item, type C-h k, and then select the menu bar with the mouse in the usual way (see Key Help).

On text-only terminals with no mouse, you can use the menu bar by typing M-` or <F10> (these run the command tmm-menubar). This command enters a mode in which you can select a menu item from the keyboard. A provisional choice appears in the echo area. You can use the up and down arrow keys to move through the menu to different choices. When you have found the choice you want, type <RET> to select it.

Each menu item also has an assigned letter or digit which designates that item; it is usually the initial of some word in the item's name. This letter or digit is separated from the item name by ‘=>’. You can type the item's letter or digit to select the item.

Some of the commands in the menu bar have ordinary key bindings as well; if so, the menu lists one equivalent key binding in parentheses after the item itself.

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2 Kinds of User Input

GNU Emacs uses an extension of the ASCII character set for keyboard input; it also accepts non-character input events including function keys and mouse button actions.

ASCII consists of 128 character codes. Some of these codes are assigned graphic symbols such as ‘a’ and ‘=’; the rest are control characters, such as Control-a (usually written C-a for short). C-a gets its name from the fact that you type it by holding down the <CTRL> key while pressing a.

Some ASCII control characters have special names, and most terminals have special keys you can type them with: for example, <RET>, <TAB>, <DEL> and <ESC>. The space character is usually referred to below as <SPC>, even though strictly speaking it is a graphic character whose graphic happens to be blank. Some keyboards have a key labeled “linefeed” which is an alias for C-j.

Emacs extends the ASCII character set with thousands more printing characters (see International), additional control characters, and a few more modifiers that can be combined with any character.

On ASCII terminals, there are only 32 possible control characters. These are the control variants of letters and ‘@[]\^_’. In addition, the shift key is meaningless with control characters: C-a and C-A are the same character, and Emacs cannot distinguish them.

But the Emacs character set has room for control variants of all printing characters, and for distinguishing between C-a and C-A. The X Window System makes it possible to enter all these characters. For example, C-- (that's Control-Minus) and C-5 are meaningful Emacs commands under X.

Another Emacs character-set extension is additional modifier bits. Only one modifier bit is commonly used; it is called Meta. Every character has a Meta variant; examples include Meta-a (normally written M-a, for short), M-A (not the same character as M-a, but those two characters normally have the same meaning in Emacs), M-<RET>, and M-C-a. For reasons of tradition, we usually write C-M-a rather than M-C-a; logically speaking, the order in which the modifier keys <CTRL> and <META> are mentioned does not matter.

Some terminals have a <META> key, and allow you to type Meta characters by holding this key down. Thus, Meta-a is typed by holding down <META> and pressing a. The <META> key works much like the <SHIFT> key. Such a key is not always labeled <META>, however, as this function is often a special option for a key with some other primary purpose. Sometimes it is labeled <ALT> or <EDIT>; on a Sun keyboard, it may have a diamond on it.

If there is no <META> key, you can still type Meta characters using two-character sequences starting with <ESC>. Thus, you can enter M-a by typing <ESC> a. You can enter C-M-a by typing <ESC> C-a. Unlike <META>, which modifies other characters, <ESC> is a separate character. You don't hold down <ESC> while typing the next character; instead, you press it and release it, then you enter the next character. <ESC> is allowed on terminals with <META> keys, too, in case you have formed a habit of using it.

The X Window System provides several other modifier keys that can be applied to any input character. These are called <SUPER>, <HYPER> and <ALT>. We write ‘s-’, ‘H-’ and ‘A-’ to say that a character uses these modifiers. Thus, s-H-C-x is short for Super-Hyper-Control-x. Not all X terminals actually provide keys for these modifier flags—in fact, many terminals have a key labeled <ALT> which is really a <META> key. The standard key bindings of Emacs do not include any characters with these modifiers. But you can assign them meanings of your own by customizing Emacs.

If your keyboard lacks one of these modifier keys, you can enter it using C-x @: C-x @ h adds the “hyper” flag to the next character, C-x @ s adds the “super” flag, and C-x @ a adds the “alt” flag. For instance, C-x @ h C-a is a way to enter Hyper-Control-a. (Unfortunately there is no way to add two modifiers by using C-x @ twice for the same character, because the first one goes to work on the C-x.)

Keyboard input includes keyboard keys that are not characters at all: for example function keys and arrow keys. Mouse buttons are also outside the gamut of characters. You can modify these events with the modifier keys <CTRL>, <META>, <SUPER>, <HYPER> and <ALT>, just like keyboard characters.

Input characters and non-character inputs are collectively called input events. See Input Events, for more information. If you are not doing Lisp programming, but simply want to redefine the meaning of some characters or non-character events, see Customization.

ASCII terminals cannot really send anything to the computer except ASCII characters. These terminals use a sequence of characters to represent each function key. But that is invisible to the Emacs user, because the keyboard input routines recognize these special sequences and convert them to function key events before any other part of Emacs gets to see them.

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3 Keys

A key sequence (key, for short) is a sequence of input events that are meaningful as a unit—as “a single command.” Some Emacs command sequences are just one character or one event; for example, just C-f is enough to move forward one character in the buffer. But Emacs also has commands that take two or more events to invoke.

If a sequence of events is enough to invoke a command, it is a complete key. Examples of complete keys include C-a, X, <RET>, <NEXT> (a function key), <DOWN> (an arrow key), C-x C-f, and C-x 4 C-f. If it isn't long enough to be complete, we call it a prefix key. The above examples show that C-x and C-x 4 are prefix keys. Every key sequence is either a complete key or a prefix key.

Most single characters constitute complete keys in the standard Emacs command bindings. A few of them are prefix keys. A prefix key combines with the following input event to make a longer key sequence, which may itself be complete or a prefix. For example, C-x is a prefix key, so C-x and the next input event combine to make a two-event key sequence. Most of these key sequences are complete keys, including C-x C-f and C-x b. A few, such as C-x 4 and C-x r, are themselves prefix keys that lead to three-event key sequences. There's no limit to the length of a key sequence, but in practice people rarely use sequences longer than four events.

By contrast, you can't add more events onto a complete key. For example, the two-event sequence C-f C-k is not a key, because the C-f is a complete key in itself. It's impossible to give C-f C-k an independent meaning as a command. C-f C-k is two key sequences, not one.

All told, the prefix keys in Emacs are C-c, C-h, C-x, C-x <RET>, C-x @, C-x a, C-x n, C-x r, C-x v, C-x 4, C-x 5, C-x 6, <ESC>, M-o and M-g. (<F1> and <F2> are aliases for C-h and C-x 6.) But this list is not cast in concrete; it is just a matter of Emacs's standard key bindings. If you customize Emacs, you can make new prefix keys, or eliminate these. See Key Bindings.

If you do make or eliminate prefix keys, that changes the set of possible key sequences. For example, if you redefine C-f as a prefix, C-f C-k automatically becomes a key (complete, unless you define that too as a prefix). Conversely, if you remove the prefix definition of C-x 4, then C-x 4 f (or C-x 4 anything) is no longer a key.

Typing the help character (C-h or <F1>) after a prefix key displays a list of the commands starting with that prefix. There are a few prefix keys for which C-h does not work—for historical reasons, they have other meanings for C-h which are not easy to change. But <F1> should work for all prefix keys.

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4 Keys and Commands

This manual is full of passages that tell you what particular keys do. But Emacs does not assign meanings to keys directly. Instead, Emacs assigns meanings to named commands, and then gives keys their meanings by binding them to commands.

Every command has a name chosen by a programmer. The name is usually made of a few English words separated by dashes; for example, next-line or forward-word. A command also has a function definition which is a Lisp program; this is what makes the command do what it does. In Emacs Lisp, a command is actually a special kind of Lisp function; one which specifies how to read arguments for it and call it interactively. For more information on commands and functions, see What Is a Function. (The definition we use in this manual is simplified slightly.)

The bindings between keys and commands are recorded in various tables called keymaps. See Keymaps.

When we say that “C-n moves down vertically one line” we are glossing over a distinction that is irrelevant in ordinary use but is vital in understanding how to customize Emacs. It is the command next-line that is programmed to move down vertically. C-n has this effect because it is bound to that command. If you rebind C-n to the command forward-word then C-n will move forward by words instead. Rebinding keys is a common method of customization.

In the rest of this manual, we usually ignore this distinction to keep things simple. We will often speak of keys like C-n as commands, even though strictly speaking a key is bound to some command. To give the information needed for customization, we state the name of the command which really does the work in parentheses after mentioning the key that runs it. For example, we will say that “The command C-n (next-line) moves point vertically down,” meaning that next-line is a command that moves vertically down, and C-n is a key that is normally bound to it.

While we are on the subject of information for customization only, it's a good time to tell you about variables. Often the description of a command will say, “To change this, set the variable mumble-foo.” A variable is a name used to remember a value. Most of the variables documented in this manual exist just to facilitate customization: some command or other part of Emacs examines the variable and behaves differently according to the value that you set. Until you are interested in customizing, you can ignore the information about variables. When you are ready to be interested, read the basic information on variables, and then the information on individual variables will make sense. See Variables.

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5 Character Set for Text

Text in Emacs buffers is a sequence of 8-bit bytes. Each byte can hold a single ASCII character. Both ASCII control characters (octal codes 000 through 037, and 0177) and ASCII printing characters (codes 040 through 0176) are allowed; however, non-ASCII control characters cannot appear in a buffer. The other modifier flags used in keyboard input, such as Meta, are not allowed in buffers either.

Some ASCII control characters serve special purposes in text, and have special names. For example, the newline character (octal code 012) is used in the buffer to end a line, and the tab character (octal code 011) is used for indenting to the next tab stop column (normally every 8 columns). See Text Display.

Non-ASCII printing characters can also appear in buffers. When multibyte characters are enabled, you can use any of the non-ASCII printing characters that Emacs supports. They have character codes starting at 256, octal 0400, and each one is represented as a sequence of two or more bytes. See International. Single-byte characters with codes 128 through 255 can also appear in multibyte buffers.

If you disable multibyte characters, then you can use only one alphabet of non-ASCII characters, but they all fit in one byte. They use codes 0200 through 0377. See Single-Byte Character Support.

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6 Entering and Exiting Emacs

The usual way to invoke Emacs is with the shell command emacs. Emacs clears the screen and then displays an initial help message and copyright notice. Some operating systems discard all type-ahead when Emacs starts up; they give Emacs no way to prevent this. Therefore, it is advisable to wait until Emacs clears the screen before typing your first editing command.

If you run Emacs from a shell window under the X Window System, run it in the background with emacs&. This way, Emacs does not tie up the shell window, so you can use that to run other shell commands while Emacs operates its own X windows. You can begin typing Emacs commands as soon as you direct your keyboard input to the Emacs frame.

When Emacs starts up, it creates a buffer named ‘*scratch*’. That's the buffer you start out in. The ‘*scratch*’ buffer uses Lisp Interaction mode; you can use it to type Lisp expressions and evaluate them, or you can ignore that capability and simply doodle. (You can specify a different major mode for this buffer by setting the variable initial-major-mode in your init file. See Init File.)

It is possible to specify files to be visited, Lisp files to be loaded, and functions to be called, by giving Emacs arguments in the shell command line. See Emacs Invocation. But we don't recommend doing this. The feature exists mainly for compatibility with other editors.

Many other editors are designed to be started afresh each time you want to edit. You edit one file and then exit the editor. The next time you want to edit either another file or the same one, you must run the editor again. With these editors, it makes sense to use a command-line argument to say which file to edit.

But starting a new Emacs each time you want to edit a different file does not make sense. This would fail to take advantage of Emacs's ability to visit more than one file in a single editing session, and it would lose the other accumulated context, such as the kill ring, registers, undo history, and mark ring, that are useful for operating on multiple files.

The recommended way to use GNU Emacs is to start it only once, just after you log in, and do all your editing in the same Emacs session. Each time you want to edit a different file, you visit it with the existing Emacs, which eventually comes to have many files in it ready for editing. Usually you do not kill the Emacs until you are about to log out. See Files, for more information on visiting more than one file.

If you want to edit a file from another program and already have Emacs running, you can use the emacsclient program to open a file in the already running Emacs. See Emacs Server, for more information on editing files with Emacs from other programs.

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7 Exiting Emacs

There are two commands for exiting Emacs because there are three kinds of exiting: suspending Emacs, Iconifying Emacs, and killing Emacs.

Suspending means stopping Emacs temporarily and returning control to its parent process (usually a shell), allowing you to resume editing later in the same Emacs job, with the same buffers, same kill ring, same undo history, and so on. This is the usual way to exit Emacs when running on a text terminal.

Iconifying means replacing the Emacs frame with a small box somewhere on the screen. This is the usual way to exit Emacs when you're using a graphics terminal.

Killing Emacs means destroying the Emacs job. You can run Emacs again later, but you will get a fresh Emacs; there is no way to resume the same editing session after it has been killed.

Suspend Emacs (suspend-emacs) or iconify a frame (iconify-or-deiconify-frame).
C-x C-c
Kill Emacs (save-buffers-kill-emacs).

To suspend or iconify Emacs, type C-z (suspend-emacs). On text terminals, this suspends Emacs. On graphics terminals, it iconifies the Emacs frame.

Suspending Emacs takes you back to the shell from which you invoked Emacs. You can resume Emacs with the shell command %emacs in most common shells. On systems that don't support suspending programs, C-z starts an inferior shell that communicates directly with the terminal. Emacs waits until you exit the subshell. (The way to do that is probably with C-d or exit, but it depends on which shell you use.) The only way on these systems to get back to the shell from which Emacs was run (to log out, for example) is to kill Emacs.

Suspending can fail if you run Emacs under a shell that doesn't support suspending programs, even if the system itself does support it. In such a case, you can set the variable cannot-suspend to a non-nil value to force C-z to start an inferior shell. (One might also describe Emacs's parent shell as “inferior” for failing to support job control properly, but that is a matter of taste.)

On graphics terminals, C-z has a different meaning: it runs the command iconify-or-deiconify-frame, which temporarily iconifies (or “minimizes”) the selected Emacs frame (see Frames). Then you can use the window manager to get back to a shell window.

To exit and kill Emacs, type C-x C-c (save-buffers-kill-emacs). A two-character key is used for this to make it harder to type by accident. This command first offers to save any modified file-visiting buffers. If you do not save them all, it asks for reconfirmation with yes before killing Emacs, since any changes not saved will be lost forever. Also, if any subprocesses are still running, C-x C-c asks for confirmation about them, since killing Emacs will also kill the subprocesses.

If the value of the variable confirm-kill-emacs is non-nil, C-x C-c assumes that its value is a predicate function, and calls that function. If the result is non-nil, the session is killed, otherwise Emacs continues to run. One convenient function to use as the value of confirm-kill-emacs is the function yes-or-no-p. The default value of confirm-kill-emacs is nil.

There is no way to resume an Emacs session once you have killed it. You can, however, arrange for Emacs to record certain session information when you kill it, such as which files are visited, so that the next time you start Emacs it will try to visit the same files and so on. See Saving Emacs Sessions.

The operating system usually listens for certain special characters whose meaning is to kill or suspend the program you are running. This operating system feature is turned off while you are in Emacs. The meanings of C-z and C-x C-c as keys in Emacs were inspired by the use of C-z and C-c on several operating systems as the characters for stopping or killing a program, but that is their only relationship with the operating system. You can customize these keys to run any commands of your choice (see Keymaps).

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8 Basic Editing Commands

We now give the basics of how to enter text, make corrections, and save the text in a file. If this material is new to you, you might learn it more easily by running the Emacs learn-by-doing tutorial. To use the tutorial, run Emacs and type Control-h t (help-with-tutorial).

To clear the screen and redisplay, type C-l (recenter).

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8.1 Inserting Text

To insert printing characters into the text you are editing, just type them. This inserts the characters you type into the buffer at the cursor (that is, at point; see Point). The cursor moves forward, and any text after the cursor moves forward too. If the text in the buffer is ‘FOOBAR’, with the cursor before the ‘B’, then if you type XX, you get ‘FOOXXBAR’, with the cursor still before the ‘B’.

To delete text you have just inserted, use the large key labeled <DEL>, <BACKSPACE> or <DELETE> which is a short distance above the <RET> or <ENTER> key. This is the key you normally use, outside Emacs, for erasing the last character that you typed. Regardless of the label on that key, Emacs thinks of it as <DEL>, and that's what we call it in this manual.

The <DEL> key deletes the character before the cursor. As a consequence, the cursor and all the characters after it move backwards. If you type a printing character and then type <DEL>, they cancel out.

On most computers, Emacs recognizes automatically which key ought to be <DEL>, and sets it up that way. But in some cases, especially with text-only terminals, you will need to tell Emacs which key to use for that purpose. If the large key not far above the <RET> or <ENTER> key doesn't delete backwards, you need to do this. See DEL Does Not Delete, for an explanation of how.

Most PC keyboards have both a <BACKSPACE> key a short ways above <RET> or <ENTER>, and a <DELETE> key elsewhere. On these keyboards, Emacs supports when possible the usual convention that the <BACKSPACE> key deletes backwards (it is <DEL>), while the <DELETE> key deletes “forwards,” deleting the character after point, the one underneath the cursor, like C-d (see below).

To end a line and start typing a new one, type <RET>. This inserts a newline character in the buffer. If point is in the middle of a line, the effect is to split the line. Typing <DEL> when the cursor is at the beginning of a line deletes the preceding newline, thus joining the line with the preceding line.

Emacs can split lines automatically when they become too long, if you turn on a special minor mode called Auto Fill mode. See Filling, for how to use Auto Fill mode.

If you prefer to have text characters replace (overwrite) existing text rather than shove it to the right, you can enable Overwrite mode, a minor mode. See Minor Modes.

Direct insertion works for printing characters and <SPC>, but other characters act as editing commands and do not insert themselves. If you need to insert a control character or a character whose code is above 200 octal, you must quote it by typing the character Control-q (quoted-insert) first. (This character's name is normally written C-q for short.) There are two ways to use C-q:

When multibyte characters are enabled, if you specify a code in the range 0200 through 0377 octal, C-q assumes that you intend to use some ISO 8859-n character set, and converts the specified code to the corresponding Emacs character code. See Enabling Multibyte. You select which of the ISO 8859 character sets to use through your choice of language environment (see Language Environments).

To use decimal or hexadecimal instead of octal, set the variable read-quoted-char-radix to 10 or 16. If the radix is greater than 10, some letters starting with a serve as part of a character code, just like digits.

A numeric argument to C-q specifies how many copies of the quoted character should be inserted (see Arguments).

Customization information: <DEL> in most modes runs the command delete-backward-char; <RET> runs the command newline, and self-inserting printing characters run the command self-insert, which inserts whatever character was typed to invoke it. Some major modes rebind <DEL> to other commands.

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8.2 Changing the Location of Point

To do more than insert characters, you have to know how to move point (see Point). The simplest way to do this is with arrow keys, or by clicking the left mouse button where you want to move to.

There are also control and meta characters for cursor motion. Some are equivalent to the arrow keys (these date back to the days before terminals had arrow keys, and are usable on terminals which don't have them). Others do more sophisticated things.

Move to the beginning of the line (move-beginning-of-line).
Move to the end of the line (move-end-of-line).
Move forward one character (forward-char). The right-arrow key does the same thing.
Move backward one character (backward-char). The left-arrow key has the same effect.
Move forward one word (forward-word).
Move backward one word (backward-word).
Move down one line, vertically (next-line). This command attempts to keep the horizontal position unchanged, so if you start in the middle of one line, you end in the middle of the next. The down-arrow key does the same thing.
Move up one line, vertically (previous-line). The up-arrow key has the same effect.
Move point to left margin, vertically centered in the window (move-to-window-line). Text does not move on the screen.

A numeric argument says which screen line to place point on. It counts screen lines down from the top of the window (zero for the top line). A negative argument counts lines from the bottom (−1 for the bottom line).

Move to the top of the buffer (beginning-of-buffer). With numeric argument n, move to n/10 of the way from the top. See Arguments, for more information on numeric arguments.
Move to the end of the buffer (end-of-buffer).
Scroll the display one screen forward, and move point if necessary to put it on the screen (scroll-up). This doesn't always move point, but it is commonly used to do so. If your keyboard has a <PAGEDOWN> or <PRIOR> key, it does the same thing.

Scrolling commands are further described in Scrolling.

Scroll one screen backward, and move point if necessary to put it on the screen (scroll-down). This doesn't always move point, but it is commonly used to do so. If your keyboard has a <PAGEUP> or <NEXT> key, it does the same thing.
M-x goto-char
Read a number n and move point to buffer position n. Position 1 is the beginning of the buffer.
M-g M-g
M-g g
M-x goto-line
Read a number n and move point to the beginning of line number n. Line 1 is the beginning of the buffer. If point is on or just after a number, then that is the default for n, if you just press <RET> with an empty minibuffer.
C-x C-n
Use the current column of point as the semipermanent goal column for C-n and C-p (set-goal-column). Henceforth, those commands always move to this column in each line moved into, or as close as possible given the contents of the line. This goal column remains in effect until canceled.
C-u C-x C-n
Cancel the goal column. Henceforth, C-n and C-p once again try to stick to a fixed horizontal position, as usual.

If you set the variable track-eol to a non-nil value, then C-n and C-p, when starting at the end of the line, move to the end of another line. Normally, track-eol is nil. See Variables, for how to set variables such as track-eol.

C-n normally stops at the end of the buffer when you use it on the last line of the buffer. But if you set the variable next-line-add-newlines to a non-nil value, C-n on the last line of a buffer creates an additional line at the end and moves down onto it.

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8.3 Erasing Text

Delete the character before point (delete-backward-char).
Delete the character after point (delete-char).
One of these keys, whichever is the large key above the <RET> or <ENTER> key, deletes the character before point, like <DEL>. If that is <BACKSPACE>, and your keyboard also has <DELETE>, then <DELETE> deletes forwards, like C-d.
Kill to the end of the line (kill-line).
Kill forward to the end of the next word (kill-word).
Kill back to the beginning of the previous word (backward-kill-word).

You already know about the <DEL> key which deletes the character before point (that is, before the cursor). Another key, Control-d (C-d for short), deletes the character after point (that is, the character that the cursor is on). This shifts the rest of the text on the line to the left. If you type C-d at the end of a line, it joins together that line and the next line.

To erase a larger amount of text, use the C-k key, which kills a line at a time. If you type C-k at the beginning or middle of a line, it kills all the text up to the end of the line. If you type C-k at the end of a line, it joins that line and the next line.

See Killing, for more flexible ways of killing text.

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8.4 Undoing Changes

You can undo all the recent changes in the buffer text, up to a certain point. Each buffer records changes individually, and the undo command always applies to the current buffer. Usually each editing command makes a separate entry in the undo records, but some commands such as query-replace make many entries, and very simple commands such as self-inserting characters are often grouped to make undoing less tedious.

C-x u
Undo one batch of changes—usually, one command worth (undo).
The same.
C-u C-x u
Undo one batch of changes in the region.

The command C-x u (or C-_ or C-/) is how you undo. The first time you give this command, it undoes the last change. Point moves back to where it was before the command that made the change.

Consecutive repetitions of C-_ or C-x u undo earlier and earlier changes, back to the limit of the undo information available. If all recorded changes have already been undone, the undo command displays an error message and does nothing.

Any command other than an undo command breaks the sequence of undo commands. Starting from that moment, the previous undo commands become ordinary changes that you can undo. Thus, to redo changes you have undone, type C-f or any other command that will harmlessly break the sequence of undoing, then type more undo commands. On the other hand, if you want to ignore previous undo commands, use M-x undo-only. This is like undo, but will not redo changes you have just undone.

Ordinary undo applies to all changes made in the current buffer. You can also perform selective undo, limited to the current region (see Mark). To do this, specify the region you want, then run the undo command with a prefix argument (the value does not matter): C-u C-x u or C-u C-_. This undoes the most recent change in the region. To undo further changes in the same region, repeat the undo command (no prefix argument is needed). In Transient Mark mode (see Transient Mark), any use of undo when there is an active region performs selective undo; you do not need a prefix argument.

If you notice that a buffer has been modified accidentally, the easiest way to recover is to type C-_ repeatedly until the stars disappear from the front of the mode line. At this time, all the modifications you made have been canceled. Whenever an undo command makes the stars disappear from the mode line, it means that the buffer contents are the same as they were when the file was last read in or saved.

If you do not remember whether you changed the buffer deliberately, type C-_ once. When you see the last change you made undone, you will see whether it was an intentional change. If it was an accident, leave it undone. If it was deliberate, redo the change as described above.

Not all buffers record undo information. Buffers whose names start with spaces don't; these buffers are used internally by Emacs and its extensions to hold text that users don't normally look at or edit.

You cannot undo mere cursor motion; only changes in the buffer contents save undo information. However, some cursor motion commands set the mark, so if you use these commands from time to time, you can move back to the neighborhoods you have moved through by popping the mark ring (see Mark Ring).

When the undo information for a buffer becomes too large, Emacs discards the oldest undo information from time to time (during garbage collection). You can specify how much undo information to keep by setting three variables: undo-limit, undo-strong-limit, and undo-outer-limit. Their values are expressed in units of bytes of space.

The variable undo-limit sets a soft limit: Emacs keeps undo data for enough commands to reach this size, and perhaps exceed it, but does not keep data for any earlier commands beyond that. Its default value is 20000. The variable undo-strong-limit sets a stricter limit: a previous command (not the most recent one) which pushes the size past this amount is itself forgotten. The default value of undo-strong-limit is 30000.

Regardless of the values of those variables, the most recent change is never discarded unless it gets bigger than undo-outer-limit (normally 3,000,000). At that point, Emacs discards the undo data and warns you about it. This is the only situation in which you cannot undo the last command. If this happens, you can increase the value of undo-outer-limit to make it even less likely to happen in the future. But if you didn't expect the command to create such large undo data, then it is probably a bug and you should report it. See Reporting Bugs.

The reason the undo command has three key bindings, C-x u, C-_ and C-/, is that it is worthy of a single-character key, but C-x u is more straightforward for beginners to type.

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8.5 Files

The commands described above are sufficient for creating and altering text in an Emacs buffer; the more advanced Emacs commands just make things easier. But to keep any text permanently you must put it in a file. Files are named units of text which are stored by the operating system for you to retrieve later by name. To look at or use the contents of a file in any way, including editing the file with Emacs, you must specify the file name.

Consider a file named /usr/rms/foo.c. In Emacs, to begin editing this file, type

     C-x C-f /usr/rms/foo.c <RET>

Here the file name is given as an argument to the command C-x C-f (find-file). That command uses the minibuffer to read the argument, and you type <RET> to terminate the argument (see Minibuffer).

Emacs obeys the command by visiting the file: creating a buffer, copying the contents of the file into the buffer, and then displaying the buffer for you to edit. If you alter the text, you can save the new text in the file by typing C-x C-s (save-buffer). This makes the changes permanent by copying the altered buffer contents back into the file /usr/rms/foo.c. Until you save, the changes exist only inside Emacs, and the file foo.c is unaltered.

To create a file, just visit the file with C-x C-f as if it already existed. This creates an empty buffer in which you can insert the text you want to put in the file. The file is actually created when you save this buffer with C-x C-s.

Of course, there is a lot more to learn about using files. See Files.

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8.6 Help

If you forget what a key does, you can find out with the Help character, which is C-h (or <F1>, which is an alias for C-h). Type C-h k followed by the key you want to know about; for example, C-h k C-n tells you all about what C-n does. C-h is a prefix key; C-h k is just one of its subcommands (the command describe-key). The other subcommands of C-h provide different kinds of help. Type C-h twice to get a description of all the help facilities. See Help.

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8.7 Blank Lines

Here are special commands and techniques for putting in and taking out blank lines.

Insert one or more blank lines after the cursor (open-line).
C-x C-o
Delete all but one of many consecutive blank lines (delete-blank-lines).

When you want to insert a new line of text before an existing line, you can do it by typing the new line of text, followed by <RET>. However, it may be easier to see what you are doing if you first make a blank line and then insert the desired text into it. This is easy to do using the key C-o (open-line), which inserts a newline after point but leaves point in front of the newline. After C-o, type the text for the new line. C-o F O O has the same effect as F O O <RET>, except for the final location of point.

You can make several blank lines by typing C-o several times, or by giving it a numeric argument to tell it how many blank lines to make. See Arguments, for how. If you have a fill prefix, the C-o command inserts the fill prefix on the new line, when you use it at the beginning of a line. See Fill Prefix.

The easy way to get rid of extra blank lines is with the command C-x C-o (delete-blank-lines). C-x C-o in a run of several blank lines deletes all but one of them. C-x C-o on a solitary blank line deletes that blank line. When point is on a nonblank line, C-x C-o deletes any blank lines following that nonblank line.

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8.8 Continuation Lines

If you add too many characters to one line without breaking it with <RET>, the line grows to occupy two (or more) lines on the screen. On graphical displays, Emacs indicates line wrapping with small bent arrows in the fringes to the left and right of the window. On text-only terminals, Emacs displays a ‘\’ character at the right margin of a screen line if it is not the last in its text line. This ‘\’ character says that the following screen line is not really a distinct line in the text, just a continuation of a line too long to fit the screen. Continuation is also called line wrapping.

When line wrapping occurs before a character that is wider than one column, some columns at the end of the previous screen line may be “empty.” In this case, Emacs displays additional ‘\’ characters in the “empty” columns, just before the ‘\’ character that indicates continuation.

Sometimes it is nice to have Emacs insert newlines automatically when a line gets too long. Continuation on the screen does not do that. Use Auto Fill mode (see Filling) if that's what you want.

As an alternative to continuation, Emacs can display long lines by truncation. This means that all the characters that do not fit in the width of the screen or window do not appear at all. ‘$’ in the last column or a small straight arrow in the fringe to the right of the window indicates a truncated line.

See Display Custom, for more information about line truncation, and other variables that affect how text is displayed.

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8.9 Cursor Position Information

Here are commands to get information about the size and position of parts of the buffer, and to count lines.

M-x what-page
Display the page number of point, and the line number within the page.
M-x what-line
Display the line number of point in the buffer.
M-x line-number-mode
M-x column-number-mode
Toggle automatic display of current line number or column number. See Optional Mode Line.
Display the number of lines in the current region (count-lines-region). See Mark, for information about the region.
C-x =
Display the character code of character after point, character position of point, and column of point (what-cursor-position).
M-x hl-line-mode
Enable or disable highlighting of the current line. See Cursor Display.
M-x size-indication-mode
Toggle automatic display of the size of the buffer. See Optional Mode Line.

M-x what-line computes the current line number and displays it in the echo area. You can also see the current line number in the mode line; see Mode Line. If you narrow the buffer, then the line number in the mode line is relative to the accessible portion (see Narrowing). By contrast, what-line shows both the line number relative to the narrowed region and the line number relative to the whole buffer.

M-x what-page counts pages from the beginning of the file, and counts lines within the page, showing both numbers in the echo area. See Pages.

While on this subject, we might as well mention M-= (count-lines-region), which displays the number of lines in the region (see Mark). See Pages, for the command C-x l which counts the lines in the current page.

The command C-x = (what-cursor-position) shows what column the cursor is in, and other miscellaneous information about point and the character after it. It displays a line in the echo area that looks like this:

     Char: c (99, #o143, #x63) point=28062 of 36168 (78%) column=53

The four values after ‘Char:’ describe the character that follows point, first by showing it and then by giving its character code in decimal, octal and hex. For a non-ASCII multibyte character, these are followed by ‘file’ and the character's representation, in hex, in the buffer's coding system, if that coding system encodes the character safely and with a single byte (see Coding Systems). If the character's encoding is longer than one byte, Emacs shows ‘file ...’.

However, if the character displayed is in the range 0200 through 0377 octal, it may actually stand for an invalid UTF-8 byte read from a file. In Emacs, that byte is represented as a sequence of 8-bit characters, but all of them together display as the original invalid byte, in octal code. In this case, C-x = shows ‘part of display ...’ instead of ‘file’.

point=’ is followed by the position of point expressed as a character count. The front of the buffer counts as position 1, one character later as 2, and so on. The next, larger, number is the total number of characters in the buffer. Afterward in parentheses comes the position expressed as a percentage of the total size.

column=’ is followed by the horizontal position of point, in columns from the left edge of the window.

If the buffer has been narrowed, making some of the text at the beginning and the end temporarily inaccessible, C-x = displays additional text describing the currently accessible range. For example, it might display this:

     Char: C (67, #o103, #x43) point=252 of 889 (28%) <231-599> column=0

where the two extra numbers give the smallest and largest character position that point is allowed to assume. The characters between those two positions are the accessible ones. See Narrowing.

If point is at the end of the buffer (or the end of the accessible part), the C-x = output does not describe a character after point. The output might look like this:

     point=36169 of 36168 (EOB) column=0

C-u C-x = displays the following additional information about a character.

Here's an example showing the Latin-1 character A with grave accent, in a buffer whose coding system is iso-latin-1, whose terminal coding system is iso-latin-1 (so the terminal actually displays the character as ‘À’), and which has font-lock-mode (see Font Lock) enabled:

       character: À (2240, #o4300, #x8c0, U+00C0)
         charset: [latin-iso8859-1]
                  (Right-Hand Part of Latin Alphabet 1...
      code point: [64]
          syntax: w 	which means: word
        category: l:Latin
        to input: type "`A" with [latin-1-prefix]
     buffer code: #x81 #xC0
       file code: ESC #x2C #x41 #x40 (encoded by coding system iso-2022-7bit)
         display: terminal code #xC0
     There are text properties here:
       fontified            t

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8.10 Numeric Arguments

In mathematics and computer usage, the word argument means “data provided to a function or operation.” You can give any Emacs command a numeric argument (also called a prefix argument). Some commands interpret the argument as a repetition count. For example, C-f with an argument of ten moves forward ten characters instead of one. With these commands, no argument is equivalent to an argument of one. Negative arguments tell most such commands to move or act in the opposite direction.

If your terminal keyboard has a <META> key (labeled <ALT> on PC keyboards), the easiest way to specify a numeric argument is to type digits and/or a minus sign while holding down the <META> key. For example,

     M-5 C-n

would move down five lines. The characters Meta-1, Meta-2, and so on, as well as Meta--, do this because they are keys bound to commands (digit-argument and negative-argument) that are defined to contribute to an argument for the next command. Meta-- without digits normally means −1. Digits and - modified with Control, or Control and Meta, also specify numeric arguments.

Another way of specifying an argument is to use the C-u (universal-argument) command followed by the digits of the argument. With C-u, you can type the argument digits without holding down modifier keys; C-u works on all terminals. To type a negative argument, type a minus sign after C-u. Just a minus sign without digits normally means −1.

C-u followed by a character which is neither a digit nor a minus sign has the special meaning of “multiply by four.” It multiplies the argument for the next command by four. C-u twice multiplies it by sixteen. Thus, C-u C-u C-f moves forward sixteen characters. This is a good way to move forward “fast,” since it moves about 1/5 of a line in the usual size screen. Other useful combinations are C-u C-n, C-u C-u C-n (move down a good fraction of a screen), C-u C-u C-o (make “a lot” of blank lines), and C-u C-k (kill four lines).

Some commands care only about whether there is an argument, and not about its value. For example, the command M-q (fill-paragraph) with no argument fills text; with an argument, it justifies the text as well. (See Filling, for more information on M-q.) Plain C-u is a handy way of providing an argument for such commands.

Some commands use the value of the argument as a repeat count, but do something peculiar when there is no argument. For example, the command C-k (kill-line) with argument n kills n lines, including their terminating newlines. But C-k with no argument is special: it kills the text up to the next newline, or, if point is right at the end of the line, it kills the newline itself. Thus, two C-k commands with no arguments can kill a nonblank line, just like C-k with an argument of one. (See Killing, for more information on C-k.)

A few commands treat a plain C-u differently from an ordinary argument. A few others may treat an argument of just a minus sign differently from an argument of −1. These unusual cases are described when they come up; they are always for reasons of convenience of use of the individual command, and they are documented in the command's documentation string.

You can use a numeric argument to insert multiple copies of a character. This is straightforward unless the character is a digit; for example, C-u 6 4 a inserts 64 copies of the character ‘a’. But this does not work for inserting digits; C-u 6 4 1 specifies an argument of 641, rather than inserting anything. To separate the digit to insert from the argument, type another C-u; for example, C-u 6 4 C-u 1 does insert 64 copies of the character ‘1’.

We use the term “prefix argument” as well as “numeric argument” to emphasize that you type the argument before the command, and to distinguish these arguments from minibuffer arguments that come after the command.

Previous: Arguments, Up: Basic

8.11 Repeating a Command

Many simple commands, such as those invoked with a single key or with M-x command-name <RET>, can be repeated by invoking them with a numeric argument that serves as a repeat count (see Arguments). However, if the command you want to repeat prompts for some input, or uses a numeric argument in another way, repetition using a numeric argument might be problematical.

The command C-x z (repeat) provides another way to repeat an Emacs command many times. This command repeats the previous Emacs command, whatever that was. Repeating a command uses the same arguments that were used before; it does not read new arguments each time.

To repeat the command more than once, type additional z's: each z repeats the command one more time. Repetition ends when you type a character other than z, or press a mouse button.

For example, suppose you type C-u 2 0 C-d to delete 20 characters. You can repeat that command (including its argument) three additional times, to delete a total of 80 characters, by typing C-x z z z. The first C-x z repeats the command once, and each subsequent z repeats it once again.

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9 The Minibuffer

The minibuffer is the facility used by Emacs commands to read arguments more complicated than a single number. Minibuffer arguments can be file names, buffer names, Lisp function names, Emacs command names, Lisp expressions, and many other things, depending on the command reading the argument. You can use the usual Emacs editing commands in the minibuffer to edit the argument text.

When the minibuffer is in use, it appears in the echo area, and the terminal's cursor moves there. The beginning of the minibuffer line displays a prompt in a special color, to say what kind of input you should supply and how it will be used. Often this prompt is derived from the name of the command that the argument is for. The prompt normally ends with a colon.

Sometimes a default argument appears in parentheses before the colon; it too is part of the prompt. The default will be used as the argument value if you enter an empty argument (that is, just type <RET>). For example, commands that read buffer names always show a default, which is the name of the buffer that will be used if you type just <RET>.

The simplest way to enter a minibuffer argument is to type the text you want, terminated by <RET> which exits the minibuffer. You can cancel the command that wants the argument, and get out of the minibuffer, by typing C-g.

Since the minibuffer uses the screen space of the echo area, it can conflict with other ways Emacs customarily uses the echo area. Here is how Emacs handles such conflicts:

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9.1 Minibuffers for File Names

Sometimes the minibuffer starts out with text in it. For example, when you are supposed to give a file name, the minibuffer starts out containing the default directory, which ends with a slash. This is to inform you which directory the file will be found in if you do not specify a directory.

For example, the minibuffer might start out with these contents:

     Find File: /u2/emacs/src/

where ‘Find File: ’ is the prompt. Typing buffer.c as input specifies the file /u2/emacs/src/buffer.c. To find files in nearby directories, use ..; thus, if you type ../lisp/simple.el, you will get the file named /u2/emacs/lisp/simple.el. Alternatively, you can kill with M-<DEL> the directory names you don't want (see Words).

If you don't want any of the default, you can kill it with C-a C-k. But you don't need to kill the default; you can simply ignore it. Insert an absolute file name, one starting with a slash or a tilde, after the default directory. For example, to specify the file /etc/termcap, just insert that name, giving these minibuffer contents:

     Find File: /u2/emacs/src//etc/termcap

GNU Emacs gives a special meaning to a double slash (which is not normally a useful thing to write): it means, “ignore everything before the second slash in the pair.” Thus, ‘/u2/emacs/src/’ is ignored in the example above, and you get the file /etc/termcap. The ignored part of the file name is dimmed if the terminal allows it; to disable this, turn off file-name-shadow-mode minor mode.

If you set insert-default-directory to nil, the default directory is not inserted in the minibuffer. This way, the minibuffer starts out empty. But the name you type, if relative, is still interpreted with respect to the same default directory.

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9.2 Editing in the Minibuffer

The minibuffer is an Emacs buffer (albeit a peculiar one), and the usual Emacs commands are available for editing the text of an argument you are entering.

Since <RET> in the minibuffer is defined to exit the minibuffer, you can't use it to insert a newline in the minibuffer. To do that, type C-o or C-q C-j. (On text terminals, newline is really the ASCII character control-J.)

The minibuffer has its own window which always has space on the screen but acts as if it were not there when the minibuffer is not in use. When the minibuffer is in use, its window is just like the others; you can switch to another window with C-x o, edit text in other windows and perhaps even visit more files, before returning to the minibuffer to submit the argument. You can kill text in another window, return to the minibuffer window, and then yank the text to use it in the argument. See Windows.

There are some restrictions on the use of the minibuffer window, however. You cannot switch buffers in it—the minibuffer and its window are permanently attached. Also, you cannot split or kill the minibuffer window. But you can make it taller in the normal fashion with C-x ^.

The minibuffer window expands vertically as necessary to hold the text that you put in the minibuffer. If resize-mini-windows is t (the default), the window is always resized to fit the size of the text it displays. If its value is the symbol grow-only, the window grows when the size of displayed text increases, but shrinks (back to the normal size) only when the minibuffer becomes inactive. If its value is nil, you have to adjust the height yourself.

The variable max-mini-window-height controls the maximum height for resizing the minibuffer window: a floating-point number specifies a fraction of the frame's height; an integer specifies the maximum number of lines; nil means do not resize the minibuffer window automatically. The default value is 0.25.

If, while in the minibuffer, you issue a command that displays help text of any sort in another window, you can use the C-M-v command while in the minibuffer to scroll the help text. (M-<PAGEUP> and M-<PAGEDOWN> also operate on that help text.) This lasts until you exit the minibuffer. This feature is especially useful when you display a buffer listing possible completions. See Other Window.

Emacs normally disallows most commands that use the minibuffer while the minibuffer is active. This rule is to prevent recursive minibuffers from confusing novice users. If you want to be able to use such commands in the minibuffer, set the variable enable-recursive-minibuffers to a non-nil value.

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9.3 Completion

For certain kinds of arguments, you can use completion to enter the argument value. Completion means that you type part of the argument, then Emacs visibly fills in the rest, or as much as can be determined from the part you have typed.

When completion is available, certain keys—<TAB>, <RET>, and <SPC>—are rebound to complete the text in the minibuffer before point into a longer string that it stands for, by matching it against a set of completion alternatives provided by the command reading the argument. ? is defined to display a list of possible completions of what you have inserted.

For example, when M-x uses the minibuffer to read the name of a command, it provides a list of all available Emacs command names to complete against. The completion keys match the minibuffer text against all the command names, find any additional name characters implied by the ones already present in the minibuffer, and add those characters to the ones you have given. This is what makes it possible to type M-x ins <SPC> b <RET> instead of M-x insert-buffer <RET> (for example). (<SPC> does not do completion in reading file names, because it is common to use spaces in file names on some systems.)

Case is normally significant in completion, because it is significant in most of the names that you can complete (buffer names, file names and command names). Thus, ‘fo’ does not complete to ‘Foo’. Completion does ignore case distinctions for certain arguments in which case does not matter.

Completion acts only on the text before point. If there is text in the minibuffer after point—i.e., if you move point backward after typing some text into the minibuffer—it remains unchanged.

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9.3.1 Completion Example

A concrete example may help here. If you type M-x au <TAB>, the <TAB> looks for alternatives (in this case, command names) that start with ‘au’. There are several, including auto-fill-mode and auto-save-mode—but they are all the same as far as auto-, so the ‘au’ in the minibuffer changes to ‘auto-’.

If you type <TAB> again immediately, there are multiple possibilities for the very next character—it could be any of ‘cfilrs’—so no more characters are added; instead, <TAB> displays a list of all possible completions in another window.

If you go on to type f <TAB>, this <TAB> sees ‘auto-f’. The only command name starting this way is auto-fill-mode, so completion fills in the rest of that. You now have ‘auto-fill-mode’ in the minibuffer after typing just au <TAB> f <TAB>. Note that <TAB> has this effect because in the minibuffer it is bound to the command minibuffer-complete when completion is available.

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9.3.2 Completion Commands

Here is a list of the completion commands defined in the minibuffer when completion is available.

Complete the text before point in the minibuffer as much as possible (minibuffer-complete).
Complete the minibuffer text before point, but don't go beyond one word (minibuffer-complete-word). <SPC> for completion is not available when entering a file name, since some users often put spaces in filenames.
Submit the text in the minibuffer as the argument, possibly completing first as described in the next node (minibuffer-complete-and-exit). See Strict Completion.
Display a list of all possible completions of the text in the minibuffer (minibuffer-completion-help).

<SPC> completes much like <TAB>, but never goes beyond the next hyphen or space. If you have ‘auto-f’ in the minibuffer and type <SPC>, it finds that the completion is ‘auto-fill-mode’, but it stops completing after ‘fill-’. This gives ‘auto-fill-’. Another <SPC> at this point completes all the way to ‘auto-fill-mode’. The command that implements this behavior is called minibuffer-complete-word.

Here are some commands you can use to choose a completion from a window that displays a list of completions:

Clicking mouse button 1 or 2 on a completion in the list of possible completions chooses that completion (mouse-choose-completion). You normally use this command while point is in the minibuffer, but you must click in the list of completions, not in the minibuffer itself.

Typing <PRIOR> or <PAGE-UP>, or M-v, while in the minibuffer, selects the window showing the completion list buffer (switch-to-completions). This paves the way for using the commands below. (Selecting that window in the usual ways has the same effect, but this way is more convenient.)

Typing <RET> in the completion list buffer chooses the completion that point is in or next to (choose-completion). To use this command, you must first switch windows to the window that shows the list of completions.

Typing the right-arrow key <RIGHT> in the completion list buffer moves point to the following completion (next-completion).

Typing the left-arrow key <LEFT> in the completion list buffer moves point toward the beginning of the buffer, to the previous completion (previous-completion).

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9.3.3 Strict Completion

There are three different ways that <RET> can work in completing minibuffers, depending on how the argument will be used.

The completion commands display a list of all possible completions in a window whenever there is more than one possibility for the very next character. Also, typing ? explicitly requests such a list. If the list of completions is long, you can scroll it with C-M-v (see Other Window).

Previous: Strict Completion, Up: Completion

9.3.4 Completion Options

When completion is done on file names, certain file names are usually ignored. The variable completion-ignored-extensions contains a list of strings; a file whose name ends in any of those strings is ignored as a possible completion. The standard value of this variable has several elements including ".o", ".elc", ".dvi" and "~". The effect is that, for example, ‘foo’ can complete to ‘foo.c’ even though ‘foo.o’ exists as well. However, if all the possible completions end in “ignored” strings, then they are not ignored. Ignored extensions do not apply to lists of completions—those always mention all possible completions.

If an element of the list in completion-ignored-extensions ends in a slash /, it indicates a subdirectory that should be ignored when completing file names. (Elements of completion-ignored-extensions which do not end in a slash are never considered when a completion candidate is a directory; thus, completion returns directories whose names end in .elc even though there's an element ".elc" in the list.)

Normally, a completion command that cannot determine even one additional character automatically displays a list of all possible completions. If the variable completion-auto-help is set to nil, this automatic display is disabled, so you must type ? to display the list of completions.

Partial Completion mode implements a more powerful kind of completion that can complete multiple words in parallel. For example, it can complete the command name abbreviation p-b into print-buffer, because no other command starts with two words whose initials are ‘p’ and ‘b’.

Partial completion of directories in file names uses ‘*’ to indicate the places for completion; thus, /u*/b*/f* might complete to /usr/bin/foo.

To enable this mode, use the command M-x partial-completion-mode, or customize the variable partial-completion-mode. This binds the partial completion commands to <TAB>, <SPC>, <RET>, and ?. The usual completion commands are available on M-<TAB> (or C-M-i), M-<SPC>, M-<RET> and M-?.

Another feature of Partial Completion mode is to extend find-file so that ‘<include>’ stands for the file named include in some directory in the path PC-include-file-path. If you set PC-disable-includes to non-nil, this feature is disabled.

Icomplete mode presents a constantly-updated display that tells you what completions are available for the text you've entered so far. The command to enable or disable this minor mode is M-x icomplete-mode.

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9.4 Minibuffer History

Every argument that you enter with the minibuffer is saved on a minibuffer history list so that you can use it again later in another argument. Special commands load the text of an earlier argument in the minibuffer. They discard the old minibuffer contents, so you can think of them as moving through the history of previous arguments.

Move to the next earlier argument string saved in the minibuffer history (previous-history-element).
Move to the next later argument string saved in the minibuffer history (next-history-element).
M-r regexp <RET>
Move to an earlier saved argument in the minibuffer history that has a match for regexp (previous-matching-history-element).
M-s regexp <RET>
Move to a later saved argument in the minibuffer history that has a match for regexp (next-matching-history-element).

The simplest way to reuse the saved arguments in the history list is to move through the history list one element at a time. While in the minibuffer, use M-p or up-arrow (previous-history-element) to “move to” the next earlier minibuffer input, and use M-n or down-arrow (next-history-element) to “move to” the next later input. These commands don't move the cursor, they bring different saved strings into the minibuffer. But you can think of them as “moving” through the history list.

The previous input that you fetch from the history entirely replaces the contents of the minibuffer. To use it as the argument, exit the minibuffer as usual with <RET>. You can also edit the text before you reuse it; this does not change the history element that you “moved” to, but your new argument does go at the end of the history list in its own right.

For many minibuffer arguments there is a “default” value. In some cases, the minibuffer history commands know the default value. Then you can insert the default value into the minibuffer as text by using M-n to move “into the future” in the history. Eventually we hope to make this feature available whenever the minibuffer has a default value.

There are also commands to search forward or backward through the history; they search for history elements that match a regular expression that you specify with the minibuffer. M-r (previous-matching-history-element) searches older elements in the history, while M-s (next-matching-history-element) searches newer elements. By special dispensation, these commands can use the minibuffer to read their arguments even though you are already in the minibuffer when you issue them. As with incremental searching, an upper-case letter in the regular expression makes the search case-sensitive (see Search Case).

All uses of the minibuffer record your input on a history list, but there are separate history lists for different kinds of arguments. For example, there is a list for file names, used by all the commands that read file names. (As a special feature, this history list records the absolute file name, no more and no less, even if that is not how you entered the file name.)

There are several other very specific history lists, including one for command names read by M-x, one for buffer names, one for arguments of commands like query-replace, and one for compilation commands read by compile. Finally, there is one “miscellaneous” history list that most minibuffer arguments use.

The variable history-length specifies the maximum length of a minibuffer history list; once a list gets that long, the oldest element is deleted each time an element is added. If the value of history-length is t, though, there is no maximum length and elements are never deleted.

The variable history-delete-duplicates specifies whether to delete duplicates in history. If the value of history-delete-duplicates is t, that means when adding a new history element, all previous identical elements are deleted.

Previous: Minibuffer History, Up: Minibuffer

9.5 Repeating Minibuffer Commands

Every command that uses the minibuffer at least once is recorded on a special history list, together with the values of its arguments, so that you can repeat the entire command. In particular, every use of M-x is recorded there, since M-x uses the minibuffer to read the command name.

C-x <ESC> <ESC>
Re-execute a recent minibuffer command (repeat-complex-command).
M-x list-command-history
Display the entire command history, showing all the commands C-x <ESC> <ESC> can repeat, most recent first.

C-x <ESC> <ESC> is used to re-execute a recent minibuffer-using command. With no argument, it repeats the last such command. A numeric argument specifies which command to repeat; one means the last one, and larger numbers specify earlier ones.

C-x <ESC> <ESC> works by turning the previous command into a Lisp expression and then entering a minibuffer initialized with the text for that expression. If you type just <RET>, the command is repeated as before. You can also change the command by editing the Lisp expression. Whatever expression you finally submit is what will be executed. The repeated command is added to the front of the command history unless it is identical to the most recently executed command already there.

Even if you don't understand Lisp syntax, it will probably be obvious which command is displayed for repetition. If you do not change the text, it will repeat exactly as before.

Once inside the minibuffer for C-x <ESC> <ESC>, you can use the minibuffer history commands (M-p, M-n, M-r, M-s; see Minibuffer History) to move through the history list of saved entire commands. After finding the desired previous command, you can edit its expression as usual and then resubmit it by typing <RET> as usual.

Incremental search does not, strictly speaking, use the minibuffer, but it does something similar. Although it behaves like a complex command, it normally does not appear in the history list for C-x <ESC> <ESC>. You can make it appear in the history by setting isearch-resume-in-command-history to a non-nil value. See Incremental Search.

The list of previous minibuffer-using commands is stored as a Lisp list in the variable command-history. Each element is a Lisp expression which describes one command and its arguments. Lisp programs can re-execute a command by calling eval with the command-history element.

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10 Running Commands by Name

Every Emacs command has a name that you can use to run it. Commands that are used often, or that must be quick to type, are also bound to keys—short sequences of characters—for convenient use. You can run them by name if you don't remember the keys. Other Emacs commands that do not need to be quick are not bound to keys; the only way to run them is by name. See Key Bindings, for the description of how to bind commands to keys.

By convention, a command name consists of one or more words, separated by hyphens; for example, auto-fill-mode or manual-entry. The use of English words makes the command name easier to remember than a key made up of obscure characters, even though it is more characters to type.

The way to run a command by name is to start with M-x, type the command name, and finish it with <RET>. M-x uses the minibuffer to read the command name. <RET> exits the minibuffer and runs the command. The string ‘M-x’ appears at the beginning of the minibuffer as a prompt to remind you to enter the name of a command to be run. See Minibuffer, for full information on the features of the minibuffer.

You can use completion to enter the command name. For example, you can invoke the command forward-char by name by typing either

     M-x forward-char <RET>


     M-x forw <TAB> c <RET>

Note that forward-char is the same command that you invoke with the key C-f. You can run any Emacs command by name using M-x, whether or not any keys are bound to it.

If you type C-g while the command name is being read, you cancel the M-x command and get out of the minibuffer, ending up at command level.

To pass a numeric argument to the command you are invoking with M-x, specify the numeric argument before the M-x. M-x passes the argument along to the command it runs. The argument value appears in the prompt while the command name is being read.

If the command you type has a key binding of its own, Emacs mentions this in the echo area. For example, if you type M-x forward-word, the message says that you can run the same command more easily by typing M-f. You can turn off these messages by setting suggest-key-bindings to nil.

Normally, when describing in this manual a command that is run by name, we omit the <RET> that is needed to terminate the name. Thus we might speak of M-x auto-fill-mode rather than M-x auto-fill-mode <RET>. We mention the <RET> only when there is a need to emphasize its presence, such as when we show the command together with following arguments.

M-x works by running the command execute-extended-command, which is responsible for reading the name of another command and invoking it.

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11 Help

Emacs provides extensive help features accessible through a single character, C-h. C-h is a prefix key that is used for commands that display documentation. The characters that you can type after C-h are called help options. One help option is C-h; that is how you ask for help about using C-h. To cancel, type C-g. The function key <F1> is equivalent to C-h.

C-h C-h (help-for-help) displays a list of the possible help options, each with a brief description. Before you type a help option, you can use <SPC> or <DEL> to scroll through the list.

C-h or <F1> means “help” in various other contexts as well. After a prefix key, it displays a list of the alternatives that can follow the prefix key. (A few prefix keys don't support C-h, because they define other meanings for it, but they all support <F1>.)

Most help buffers use a special major mode, Help mode, which lets you scroll conveniently with <SPC> and <DEL>. It also offers hyperlinks to URLs and further help regarding cross-referenced names, Info nodes, customization buffers and the like. See Help Mode.

If you are looking for a certain feature, but don't know where exactly it is documented, and aren't sure of the name of a related command or variable, we recommend trying these methods. Usually it is best to start with an apropos command, then try searching the manual index, then finally look in the FAQ and the package keywords.

C-h a topics <RET>
This searches for commands whose names match topics, which should be a keyword, a list of keywords, or a regular expression (see Regexps). This command displays all the matches in a new buffer. See Apropos.
C-h i d m emacs <RET> i topic <RET>
This looks up topic in the indices of the Emacs on-line manual. If there are several matches, Emacs displays the first one. You can then press , to move to other matches, until you find what you are looking for.
C-h i d m emacs <RET> s topic <RET>
Similar, but searches for topic (which can be a regular expression) in the text of the manual rather than in its indices.
C-h C-f
This brings up the Emacs FAQ. You can use the Info commands to browse it.
C-h p
Finally, you can try looking up a suitable package using keywords pertinent to the feature you need. See Library Keywords.

To find the documentation of a key sequence or a menu item, type C-h K and then type that key sequence or select the menu item. This looks up the description of the command invoked by the key or the menu in the appropriate manual (not necessarily the Emacs manual). Likewise, use C-h F for reading documentation of a command.

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11.1 Help Summary

Here is a summary of the Emacs interactive help commands. See Help Files, for other help commands that just display a pre-written file of information.

C-h a topics <RET>
Display a list of commands whose names match topics (apropos-command; see Apropos).
C-h b
Display a table of all key bindings in effect now, in this order: minor mode bindings, major mode bindings, and global bindings (describe-bindings).
C-h c key
Show the name of the command that key runs (describe-key-briefly). Here c stands for “character.” For more extensive information on key, use C-h k.
C-h d topics <RET>
Display a list of commands and variables whose documentation matches topics (apropos-documentation).
C-h e
Display the *Messages* buffer (view-echo-area-messages).
C-h f function <RET>
Display documentation on the Lisp function named function (describe-function). Since commands are Lisp functions, a command name may be used.
C-h h
Display the HELLO file, which shows examples of various character sets.
C-h i
Run Info, the program for browsing documentation files (info). The complete Emacs manual is available on-line in Info.
C-h k key
Display the name and documentation of the command that key runs (describe-key).
C-h l
Display a description of the last 100 characters you typed (view-lossage).
C-h m
Display documentation of the current major mode (describe-mode).
C-h p
Find packages by topic keyword (finder-by-keyword).
C-h s
Display the current contents of the syntax table, plus an explanation of what they mean (describe-syntax). See Syntax.
C-h t
Enter the Emacs interactive tutorial (help-with-tutorial).
C-h v var <RET>
Display the documentation of the Lisp variable var (describe-variable).
C-h w command <RET>
Show which keys run the command named command (where-is).
C-h C coding <RET>
Describe coding system coding (describe-coding-system).
C-h C <RET>
Describe the coding systems currently in use.
C-h I method <RET>
Describe an input method (describe-input-method).
C-h L language-env <RET>
Display information on the character sets, coding systems, and input methods used for language environment language-env (describe-language-environment).
C-h F function <RET>
Enter Info and go to the node documenting the Emacs function function (Info-goto-emacs-command-node).
C-h K key
Enter Info and go to the node where the key sequence key is documented (Info-goto-emacs-key-command-node).
C-h S symbol <RET>
Display the Info documentation on symbol symbol according to the programming language you are editing (info-lookup-symbol).
C-h .
Display a help message associated with special text areas, such as links in ‘*Help*’ buffers (display-local-help).

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11.2 Documentation for a Key

The most basic C-h options are C-h c (describe-key-briefly) and C-h k (describe-key). C-h c key displays in the echo area the name of the command that key is bound to. For example, C-h c C-f displays ‘forward-char’. Since command names are chosen to describe what the commands do, this is a good way to get a very brief description of what key does.

C-h k key is similar but gives more information: it displays the documentation string of the command as well as its name. This is too big for the echo area, so a window is used for the display.

C-h c and C-h k work for any sort of key sequences, including function keys and mouse events.

C-h w command <RET> tells you what keys are bound to command. It displays a list of the keys in the echo area. If it says the command is not on any key, you must use M-x to run it. C-h w runs the command where-is.

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11.3 Help by Command or Variable Name

C-h f (describe-function) reads the name of a Lisp function using the minibuffer, then displays that function's documentation string in a window. Since commands are Lisp functions, you can use this to get the documentation of a command that you know by name. For example,

     C-h f auto-fill-mode <RET>

displays the documentation of auto-fill-mode. This is the only way to get the documentation of a command that is not bound to any key (one which you would normally run using M-x).

C-h f is also useful for Lisp functions that you are planning to use in a Lisp program. For example, if you have just written the expression (make-vector len) and want to check that you are using make-vector properly, type C-h f make-vector <RET>. Because C-h f allows all function names, not just command names, you may find that some of your favorite completion abbreviations that work in M-x don't work in C-h f. An abbreviation may be unique among command names, yet fail to be unique when other function names are allowed.

The default function name for C-h f to describe, if you type just <RET>, is the name of the function called by the innermost Lisp expression in the buffer around point, provided that is a valid, defined Lisp function name. For example, if point is located following the text ‘(make-vector (car x)’, the innermost list containing point is the one that starts with ‘(make-vector’, so the default is to describe the function make-vector.

C-h f is often useful just to verify that you have the right spelling for the function name. If C-h f mentions a name from the buffer as the default, that name must be defined as a Lisp function. If that is all you want to know, just type C-g to cancel the C-h f command, then go on editing.

C-h v (describe-variable) is like C-h f but describes Lisp variables instead of Lisp functions. Its default is the Lisp symbol around or before point, but only if that is the name of a known Lisp variable. See Variables.

Help buffers describing Emacs variables and functions normally have hyperlinks to the definition, if you have the source files installed. (See Hyperlinking.) If you know Lisp (or C), this provides the ultimate documentation. If you don't know Lisp, you should learn it. If you are just using Emacs, treating Emacs as an object (file), then you don't really love it. For true intimacy with your editor, you need to read the source code.

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11.4 Apropos

A more sophisticated sort of question to ask is, “What are the commands for working with files?” The apropos commands ask such questions—they look for things whose names match an apropos pattern, which means either a word, a list of words, or a regular expression. Each apropos command displays a list of matching items in a special buffer.

C-h a pattern <RET>
Search for commands whose names match pattern.
M-x apropos <RET> pattern <RET>
Similar, but it searches for noninteractive functions and for variables, as well as commands.
M-x apropos-variable <RET> pattern <RET>
Similar, but it searches for variables only.
M-x apropos-value <RET> pattern <RET>
Similar, but it searches for variables based on their values, or functions based on their definitions.
C-h d pattern <RET>
Search the documentation strings (the built-in short descriptions) of all variables and functions (not their names) for a match for pattern.

To find the commands that work on files, type C-h a file <RET>. This displays a list of all command names that contain ‘file’, including copy-file, find-file, and so on. With each command name appears a brief description of how to use the command, and what keys you can currently invoke it with. For example, it would say that you can invoke find-file by typing C-x C-f. The a in C-h a stands for “Apropos”; C-h a runs the command apropos-command. This command normally checks only commands (interactive functions); if you specify a prefix argument, it checks noninteractive functions as well.

If you want more information about a function definition, variable or symbol property listed in the Apropos buffer, you can click on it with Mouse-1 or Mouse-2, or move there and type <RET>.

C-h a with a single word can find too many matches. Don't just give up; you can give Apropos a list of words to search for. When you specify more than one word in the apropos pattern, a name must contain at least two of the words in order to match. Thus, if you are looking for commands to kill a chunk of text before point, you could try C-h a kill back backward behind before <RET>.

For even greater flexibility, you can specify a regular expression (see Regexps). An apropos pattern is interpreted as a regular expression if it contains any of the regular expression special characters, ‘^$*+?.\[’.

Here is a set of arguments to give to C-h a that covers many classes of Emacs commands, since there are strong conventions for naming the standard Emacs commands. By giving you a feel for the naming conventions, this set should also serve to aid you in developing a technique for picking Apropos keywords.

char, line, word, sentence, paragraph, region, page, sexp, list, defun, rect, buffer, frame, window, face, file, dir, register, mode, beginning, end, forward, backward, next, previous, up, down, search, goto, kill, delete, mark, insert, yank, fill, indent, case, change, set, what, list, find, view, describe, default.

To list all Lisp symbols that contain a match for an Apropos pattern, not just the ones that are defined as commands, use the command M-x apropos instead of C-h a. This command does not check key bindings by default; specify a numeric argument if you want it to check them.

To list user-customizable variables that match an apropos pattern, use the command M-x apropos-variable. If you specify a prefix argument, it checks all variables.

The apropos-documentation command is like apropos except that it searches documentation strings instead of symbol names for matches for the specified Apropos pattern.

The apropos-value command is like apropos except that it searches variables' values for matches for the pattern. With a prefix argument, it also checks symbols' function definitions and property lists.

If the variable apropos-do-all is non-nil, the commands above all behave as if they had been given a prefix argument.

By default, Apropos lists the search results in alphabetical order. If the variable apropos-sort-by-scores is non-nil, Apropos tries to guess the relevance of each result, and displays the most relevant ones first.

By default, Apropos lists the search results for apropos-documentation in order of relevance of the match. If the variable apropos-documentation-sort-by-scores is nil, Apropos lists the symbols found in alphabetical order.

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11.5 Keyword Search for Lisp Libraries

The C-h p command lets you search the standard Emacs Lisp libraries by topic keywords. Here is a partial list of keywords you can use:

abbrevabbreviation handling, typing shortcuts, macros.
bibcode related to the bib bibliography processor.
csupport for the C language and related languages.
calendarcalendar and time management support.
commcommunications, networking, remote access to files.
convenienceconvenience features for faster editing.
datasupport for editing files of data.
docssupport for Emacs documentation.
emulationsemulations of other editors.
extensionsEmacs Lisp language extensions.
facessupport for multiple fonts.
filessupport for editing and manipulating files.
framessupport for Emacs frames and window systems.
gamesgames, jokes and amusements.
hardwaresupport for interfacing with exotic hardware.
helpsupport for on-line help systems.
hypermediasupport for links between text or other media types.
i18ninternationalization and alternate character-set support.
internalcode for Emacs internals, build process, defaults.
languagesspecialized modes for editing programming languages.
lispLisp support, including Emacs Lisp.
localcode local to your site.
maintmaintenance aids for the Emacs development group.
mailmodes for electronic-mail handling.
matchingvarious sorts of searching and matching.
mousemouse support.
multimediaimages and sound support.
newssupport for netnews reading and posting.
oopsupport for object-oriented programming.
outlinessupport for hierarchical outlining.
processesprocess, subshell, compilation, and job control support.
terminalssupport for terminal types.
texsupporting code for the TeX formatter.
toolsprogramming tools.
unixfront-ends/assistants for, or emulators of, UNIX-like features.
wpword processing.

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11.6 Help for International Language Support

You can use the command C-h L (describe-language-environment) to find out information about the support for a specific language environment. See Language Environments. This tells you which languages this language environment is useful for, and lists the character sets, coding systems, and input methods that go with it. It also shows some sample text to illustrate scripts.

The command C-h h (view-hello-file) displays the file etc/HELLO, which shows how to say “hello” in many languages.

The command C-h I (describe-input-method) describes information about input methods—either a specified input method, or by default the input method in use. See Input Methods.

The command C-h C (describe-coding-system) describes information about coding systems—either a specified coding system, or the ones currently in use. See Coding Systems.

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11.7 Help Mode Commands

Help buffers provide the same commands as View mode (see Misc File Ops), plus a few special commands of their own.

Scroll forward.
Scroll backward. On some keyboards, this key is known as <BS> or <backspace>.
Follow a cross reference at point.
Move point forward to the next cross reference.
Move point back to the previous cross reference.
Follow a cross reference that you click on.

When a function name (see Running Commands by Name) or variable name (see Variables) appears in the documentation, it normally appears inside paired single-quotes. You can click on the name with Mouse-1 or Mouse-2, or move point there and type <RET>, to view the documentation of that command or variable. Use C-c C-b to retrace your steps.

You can follow cross references to URLs (web pages) as well. When you follow a cross reference that is a URL, the browse-url command is used to view the web page in a browser of your choosing. See Browse-URL.

There are convenient commands for moving point to cross references in the help text. <TAB> (help-next-ref) moves point down to the next cross reference. Use S-<TAB> to move point up to the previous cross reference (help-previous-ref).

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11.8 Other Help Commands

C-h i (info) runs the Info program, which is used for browsing through structured documentation files. The entire Emacs manual is available within Info. Eventually all the documentation of the GNU system will be available. Type h after entering Info to run a tutorial on using Info.

With a numeric argument, C-h i selects an Info buffer with the number appended to the default ‘*info*’ buffer name (e.g. ‘*info*<2>’). This is useful if you want to browse multiple Info manuals simultaneously. If you specify just C-u as the prefix argument, C-h i prompts for the name of a documentation file. This way, you can browse a file which doesn't have an entry in the top-level Info menu. It is also handy when you need to get to the documentation quickly, and you know the exact name of the file.

There are two special help commands for accessing Emacs documentation through Info. C-h F function <RET> enters Info and goes straight to the documentation of the Emacs function function. C-h K key enters Info and goes straight to the documentation of the key key. These two keys run the commands Info-goto-emacs-command-node and Info-goto-emacs-key-command-node. You can use C-h K to find the documentation of a menu item: just select that menu item when C-h K prompts for a key.

C-h F and C-h K know about commands and keys described in manuals other than the Emacs manual. Thus, they make it easier to find the documentation of commands and keys when you are not sure which manual describes them, like when using some specialized mode.

When editing a program, if you have an Info version of the manual for the programming language, you can use the command C-h S (info-lookup-symbol) to refer to the manual documentation for a symbol (keyword, function or variable). The details of how this command works depend on the major mode.

If something surprising happens, and you are not sure what commands you typed, use C-h l (view-lossage). C-h l displays the last 100 command characters you typed in. If you see commands that you don't know, you can use C-h c to find out what they do.

To review messages that recently appeared in the echo area, use C-h e (view-echo-area-messages). This displays the buffer *Messages*, where those messages are kept.

Emacs has numerous major modes, each of which redefines a few keys and makes a few other changes in how editing works. C-h m (describe-mode) displays documentation on the current major mode, which normally describes all the commands that are changed in this mode.

C-h b (describe-bindings) and C-h s (describe-syntax) present other information about the current Emacs mode. C-h b displays a list of all the key bindings now in effect, showing the local bindings defined by the current minor modes first, then the local bindings defined by the current major mode, and finally the global bindings (see Key Bindings). C-h s displays the contents of the syntax table, with explanations of each character's syntax (see Syntax).

You can get a similar list for a particular prefix key by typing C-h after the prefix key. (There are a few prefix keys for which this does not work—those that provide their own bindings for C-h. One of these is <ESC>, because <ESC> C-h is actually C-M-h, which marks a defun.)

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11.9 Help Files

The Emacs help commands described above display the state of data bases within Emacs. Emacs has a few other help commands that display pre-written help files. These commands all have the form C-h C-char; that is, C-h followed by a control character.

The other C-h options display various files containing useful information.

C-h C-c
Displays the Emacs copying conditions (describe-copying). These are the rules under which you can copy and redistribute Emacs.
C-h C-d
Displays information on how to download or order the latest version of Emacs and other GNU software (describe-distribution).
C-h C-e
Displays the list of known Emacs problems, sometimes with suggested workarounds (view-emacs-problems).
C-h C-f
Displays the Emacs frequently-answered-questions list (view-emacs-FAQ).
C-h C-n
Displays the Emacs “news” file, which lists new Emacs features, most recent first (view-emacs-news).
C-h C-p
Displays general information about the GNU Project (describe-project).
C-h C-t
Displays the Emacs to-do list (view-todo).
C-h C-w
Displays the full details on the complete absence of warranty for GNU Emacs (describe-no-warranty).

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11.10 Help on Active Text and Tooltips

When a region of text is “active,” so that you can select it with the mouse or a key like RET, it often has associated help text. Areas of the mode line are examples. On most window systems, the help text is displayed as a “tooltip” (sometimes known as “balloon help”), when you move the mouse over the active text. See Tooltips. On some systems, it is shown in the echo area. On text-only terminals, Emacs may not be able to follow the mouse and hence will not show the help text on mouse-over.

You can also access text region help info using the keyboard. The command C-h . (display-local-help) displays any help text associated with the text at point, using the echo area. If you want help text to be displayed automatically whenever it is available at point, set the variable help-at-pt-display-when-idle to t.

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12 The Mark and the Region

Many Emacs commands operate on an arbitrary contiguous part of the current buffer. To specify the text for such a command to operate on, you set the mark at one end of it, and move point to the other end. The text between point and the mark is called the region. Emacs highlights the region whenever there is one, if you enable Transient Mark mode (see Transient Mark).

Certain Emacs commands set the mark; other editing commands do not affect it, so the mark remains where you set it last. Each Emacs buffer has its own mark, and setting the mark in one buffer has no effect on other buffers' marks. When you return to a buffer that was current earlier, its mark is at the same place as before.

The ends of the region are always point and the mark. It doesn't matter which of them was put in its current place first, or which one comes earlier in the text—the region starts from point or the mark (whichever comes first), and ends at point or the mark (whichever comes last). Every time you move point, or set the mark in a new place, the region changes.

Many commands that insert text, such as C-y (yank) and M-x insert-buffer, position point and the mark at opposite ends of the inserted text, so that the region consists of the text just inserted.

Aside from delimiting the region, the mark is also useful for remembering a spot that you may want to go back to. To make this feature more useful, each buffer remembers 16 previous locations of the mark in the mark ring.

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12.1 Setting the Mark

Here are some commands for setting the mark:

Set the mark where point is (set-mark-command).
The same.
C-x C-x
Interchange mark and point (exchange-point-and-mark).
Set point and the mark around the text you drag across.
Set the mark where point is, then move point to where you click (mouse-save-then-kill).

For example, suppose you wish to convert part of the buffer to upper case, using the C-x C-u (upcase-region) command, which operates on the text in the region. You can first go to the beginning of the text to be capitalized, type C-<SPC> to put the mark there, move to the end, and then type C-x C-u. Or, you can set the mark at the end of the text, move to the beginning, and then type C-x C-u.

The most common way to set the mark is with the C-<SPC> command (set-mark-command). This sets the mark where point is. Then you can move point away, leaving the mark behind.

There are two ways to set the mark with the mouse. You can drag mouse button one across a range of text; that puts point where you release the mouse button, and sets the mark at the other end of that range. Or you can click mouse button three, which sets the mark at point (like C-<SPC>) and then moves point where you clicked (like Mouse-1). Both of these methods copy the region into the kill ring in addition to setting the mark; that gives behavior consistent with other window-driven applications, but if you don't want to modify the kill ring, you must use keyboard commands to set the mark. See Mouse Commands.

When Emacs was developed, terminals had only one cursor, so Emacs does not show where the mark is located–you have to remember. If you enable Transient Mark mode (see below), then the region is highlighted when it is active; you can tell mark is at the other end of the highlighted region. But this only applies when the mark is active.

The usual solution to this problem is to set the mark and then use it soon, before you forget where it is. Alternatively, you can see where the mark is with the command C-x C-x (exchange-point-and-mark) which puts the mark where point was and point where the mark was. The extent of the region is unchanged, but the cursor and point are now at the previous position of the mark. In Transient Mark mode, this command also reactivates the mark.

C-x C-x is also useful when you are satisfied with the position of point but want to move the other end of the region (where the mark is); do C-x C-x to put point at that end of the region, and then move it. Using C-x C-x a second time, if necessary, puts the mark at the new position with point back at its original position.

For more facilities that allow you to go to previously set marks, see Mark Ring.

There is no such character as C-<SPC> in ASCII; when you type <SPC> while holding down <CTRL> on a text terminal, what you get is the character C-@. This key is also bound to set-mark-command–so unless you are unlucky enough to have a text terminal where typing C-<SPC> does not produce C-@, you might as well think of this character as C-<SPC>.

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12.2 Transient Mark Mode

On a terminal that supports colors, Emacs has the ability to highlight the current region. But normally it does not. Why not?

Once you have set the mark in a buffer, there is always a region in that buffer. This is because every command that sets the mark also activates it, and nothing ever deactivates it. Highlighting the region all the time would be a nuisance. So normally Emacs highlights the region only immediately after you have selected one with the mouse.

If you want region highlighting, you can use Transient Mark mode. This is a more rigid mode of operation in which the region always “lasts” only until you use it; you explicitly must set up a region for each command that uses one. In Transient Mark mode, most of the time there is no region; therefore, highlighting the region when it exists is useful and not annoying. When Transient Mark mode is enabled, Emacs always highlights the region whenever there is a region.

To enable Transient Mark mode, type M-x transient-mark-mode. This command toggles the mode; you can use the same command to turn the mode off again.

Here are the details of Transient Mark mode:

The highlighting of the region uses the region face; you can customize the appearance of the highlighted region by changing this face. See Face Customization.

When multiple windows show the same buffer, they can have different regions, because they can have different values of point (though they all share one common mark position). Ordinarily, only the selected window highlights its region (see Windows). However, if the variable highlight-nonselected-windows is non-nil, then each window highlights its own region (provided that Transient Mark mode is enabled and the mark in the window's buffer is active).

If the variable mark-even-if-inactive is non-nil in Transient Mark mode, then commands can use the mark and the region even when it is inactive. Region highlighting appears and disappears just as it normally does in Transient Mark mode, but the mark doesn't really go away when the highlighting disappears, so you can still use region commands.

Transient Mark mode is also sometimes known as “Zmacs mode” because the Zmacs editor on the MIT Lisp Machine handled the mark in a similar way.

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12.3 Using Transient Mark Mode Momentarily

If you don't like Transient Mark mode in general, you might still want to use it once in a while. To do this, type C-<SPC> C-<SPC> or C-u C-x C-x. These commands set or activate the mark, and enable Transient Mark mode only until the mark is deactivated.

Set the mark at point (like plain C-<SPC>), and enable Transient Mark mode just once until the mark is deactivated. (This is not really a separate command; you are using the C-<SPC> command twice.)
C-u C-x C-x
Activate the mark without changing it; enable Transient Mark mode just once, until the mark is deactivated. (This is the C-x C-x command, exchange-point-and-mark, with a prefix argument.)

One of the secondary features of Transient Mark mode is that certain commands operate only on the region, when there is an active region. If you don't use Transient Mark mode, the region once set never becomes inactive, so there is no way for these commands to make such a distinction. Enabling Transient Mark mode momentarily gives you a way to use these commands on the region.

Momentary use of Transient Mark mode is also a way to highlight the region for the time being.

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12.4 Operating on the Region

Once you have a region and the mark is active, here are some of the ways you can operate on the region:

Most commands that operate on the text in the region have the word region in their names.

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12.5 Commands to Mark Textual Objects

Here are the commands for placing point and the mark around a textual object such as a word, list, paragraph or page.

Set mark after end of next word (mark-word). This command and the following one do not move point.
Set mark after end of following balanced expression (mark-sexp).
Put region around current paragraph (mark-paragraph).
Put region around current defun (mark-defun).
C-x h
Put region around the entire buffer (mark-whole-buffer).
C-x C-p
Put region around current page (mark-page).

M-@ (mark-word) puts the mark at the end of the next word, while C-M-@ (mark-sexp) puts it at the end of the next balanced expression (see Expressions). These commands handle arguments just like M-f and C-M-f. If you repeat these commands, that extends the region. For example, you can type either C-u 2 M-@ or M-@ M-@ to mark the next two words. This command also extends the region when the mark is active in Transient Mark mode, regardless of the last command.

Other commands set both point and mark, to delimit an object in the buffer. For example, M-h (mark-paragraph) moves point to the beginning of the paragraph that surrounds or follows point, and puts the mark at the end of that paragraph (see Paragraphs). It prepares the region so you can indent, case-convert, or kill a whole paragraph. With prefix argument, if the argument's value is positive, M-h marks that many paragraphs starting with the one surrounding point. If the prefix argument is −n, M-h also marks n paragraphs, running back form the one surrounding point. In that last case, point moves forward to the end of that paragraph, and the mark goes at the start of the region. Repeating the M-h command extends the region, just as with M-@ and C-M-@.

C-M-h (mark-defun) similarly puts point before, and the mark after, the current (or following) major top-level definition, or defun (see Moving by Defuns). Repeating C-M-h also extends the region.

C-x C-p (mark-page) puts point before the current page, and mark at the end (see Pages). The mark goes after the terminating page delimiter (to include it in the region), while point goes after the preceding page delimiter (to exclude it). A numeric argument specifies a later page (if positive) or an earlier page (if negative) instead of the current page.

Finally, C-x h (mark-whole-buffer) sets up the entire buffer as the region, by putting point at the beginning and the mark at the end.

In Transient Mark mode, all of these commands activate the mark.

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12.6 The Mark Ring

Aside from delimiting the region, the mark is also useful for remembering a spot that you may want to go back to. To make this feature more useful, each buffer remembers 16 previous locations of the mark, in the mark ring. Commands that set the mark also push the old mark onto this ring. To return to a marked location, use C-u C-<SPC> (or C-u C-@); this is the command set-mark-command given a numeric argument. It moves point to where the mark was, and restores the mark from the ring of former marks.

If you set set-mark-command-repeat-pop to non-nil, then when you repeat the character C-<SPC> after typing C-u C-<SPC>, each repetition moves point to a previous mark position from the ring. The mark positions you move through in this way are not lost; they go to the end of the ring.

Each buffer has its own mark ring. All editing commands use the current buffer's mark ring. In particular, C-u C-<SPC> always stays in the same buffer.

Many commands that can move long distances, such as M-< (beginning-of-buffer), start by setting the mark and saving the old mark on the mark ring. This is to make it easier for you to move back later. Searches set the mark if they move point. However, in Transient Mark mode, these commands do not set the mark when the mark is already active. You can tell when a command sets the mark because it displays ‘Mark set’ in the echo area.

If you want to move back to the same place over and over, the mark ring may not be convenient enough. If so, you can record the position in a register for later retrieval (see Saving Positions in Registers).

The variable mark-ring-max specifies the maximum number of entries to keep in the mark ring. If that many entries exist and another one is pushed, the earliest one in the list is discarded. Repeating C-u C-<SPC> cycles through the positions currently in the ring.

The variable mark-ring holds the mark ring itself, as a list of marker objects, with the most recent first. This variable is local in every buffer.

Previous: Mark Ring, Up: Mark

12.7 The Global Mark Ring

In addition to the ordinary mark ring that belongs to each buffer, Emacs has a single global mark ring. It records a sequence of buffers in which you have recently set the mark, so you can go back to those buffers.

Setting the mark always makes an entry on the current buffer's mark ring. If you have switched buffers since the previous mark setting, the new mark position makes an entry on the global mark ring also. The result is that the global mark ring records a sequence of buffers that you have been in, and, for each buffer, a place where you set the mark.

The command C-x C-<SPC> (pop-global-mark) jumps to the buffer and position of the latest entry in the global ring. It also rotates the ring, so that successive uses of C-x C-<SPC> take you to earlier and earlier buffers.

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13 Killing and Moving Text

Killing means erasing text and copying it into the kill ring, from which you can bring it back into the buffer by yanking it. (Some systems use the terms “cutting” and “pasting” for these operations.) This is the most common way of moving or copying text within Emacs. Killing and yanking is very safe because Emacs remembers several recent kills, not just the last one. It is versatile, because the many commands for killing syntactic units can also be used for moving those units. But there are other ways of copying text for special purposes.

Most commands which erase text from the buffer save it in the kill ring. These commands are known as kill commands. The commands that erase text but do not save it in the kill ring are known as delete commands. The C-x u (undo) command (see Undo) can undo both kill and delete commands; the importance of the kill ring is that you can also yank the text in a different place or places. Emacs has only one kill ring for all buffers, so you can kill text in one buffer and yank it in another buffer.

The delete commands include C-d (delete-char) and <DEL> (delete-backward-char), which delete only one character at a time, and those commands that delete only spaces or newlines. Commands that can erase significant amounts of nontrivial data generally do a kill operation instead. The commands' names and individual descriptions use the words ‘kill’ and ‘delete’ to say which kind of operation they perform.

You cannot kill read-only text, since such text does not allow any kind of modification. But some users like to use the kill commands to copy read-only text into the kill ring, without actually changing it. Therefore, the kill commands work specially in a read-only buffer: they move over text, and copy it to the kill ring, without actually deleting it from the buffer. Normally, kill commands beep and display an error message when this happens. But if you set the variable kill-read-only-ok to a non-nil value, they just print a message in the echo area to explain why the text has not been erased.

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13.1 Deletion

Deletion means erasing text and not saving it in the kill ring. For the most part, the Emacs commands that delete text are those that erase just one character or only whitespace.

Delete next character (delete-char). If your keyboard has a <Delete> function key (usually located in the edit keypad), Emacs binds it to delete-char as well.
Delete previous character (delete-backward-char). Some keyboards refer to this key as a “backspace key” and label it with a left arrow.
Delete spaces and tabs around point (delete-horizontal-space).
Delete spaces and tabs around point, leaving one space (just-one-space).
C-x C-o
Delete blank lines around the current line (delete-blank-lines).
Join two lines by deleting the intervening newline, along with any indentation following it (delete-indentation).

The most basic delete commands are C-d (delete-char) and <DEL> (delete-backward-char). C-d deletes the character after point, the one the cursor is “on top of.” This doesn't move point. <DEL> deletes the character before the cursor, and moves point back. You can delete newlines like any other characters in the buffer; deleting a newline joins two lines. Actually, C-d and <DEL> aren't always delete commands; when given arguments, they kill instead, since they can erase more than one character this way.

Every keyboard has a large key, labeled <DEL>, <BACKSPACE>, <BS> or <DELETE>, which is a short distance above the <RET> or <ENTER> key and is normally used for erasing what you have typed. Regardless of the actual name on the key, in Emacs it is equivalent to <DEL>—or it should be.

Many keyboards (including standard PC keyboards) have a <BACKSPACE> key a short ways above <RET> or <ENTER>, and a <DELETE> key elsewhere. In that case, the <BACKSPACE> key is <DEL>, and the <DELETE> key is equivalent to C-d—or it should be.

Why do we say “or it should be”? When Emacs starts up using a window system, it determines automatically which key or keys should be equivalent to <DEL>. As a result, <BACKSPACE> and/or <DELETE> keys normally do the right things. But in some unusual cases Emacs gets the wrong information from the system. If these keys don't do what they ought to do, you need to tell Emacs which key to use for <DEL>. See DEL Does Not Delete, for how to do this.

On most text-only terminals, Emacs cannot tell which keys the keyboard really has, so it follows a uniform plan which may or may not fit your keyboard. The uniform plan is that the ASCII <DEL> character deletes, and the ASCII <BS> (backspace) character asks for help (it is the same as C-h). If this is not right for your keyboard, such as if you find that the key which ought to delete backwards enters Help instead, see DEL Does Not Delete.

The other delete commands are those which delete only whitespace characters: spaces, tabs and newlines. M-\ (delete-horizontal-space) deletes all the spaces and tab characters before and after point. M-<SPC> (just-one-space) does likewise but leaves a single space after point, regardless of the number of spaces that existed previously (even if there were none before). With a numeric argument n, it leaves n spaces after point.

C-x C-o (delete-blank-lines) deletes all blank lines after the current line. If the current line is blank, it deletes all blank lines preceding the current line as well (leaving one blank line, the current line). On a solitary blank line, it deletes that line.

M-^ (delete-indentation) joins the current line and the previous line, by deleting a newline and all surrounding spaces, usually leaving a single space. See M-^.

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13.2 Killing by Lines

Kill rest of line or one or more lines (kill-line).
Kill an entire line at once (kill-whole-line)

The simplest kill command is C-k. If given at the beginning of a line, it kills all the text on the line, leaving it blank. When used on a blank line, it kills the whole line including its newline. To kill an entire non-blank line, go to the beginning and type C-k twice.

More generally, C-k kills from point up to the end of the line, unless it is at the end of a line. In that case it kills the newline following point, thus merging the next line into the current one. Spaces and tabs that you can't see at the end of the line are ignored when deciding which case applies, so if point appears to be at the end of the line, you can be sure C-k will kill the newline.

When C-k is given a positive argument, it kills that many lines and the newlines that follow them (however, text on the current line before point is not killed). With a negative argument −n, it kills n lines preceding the current line (together with the text on the current line before point). Thus, C-u - 2 C-k at the front of a line kills the two previous lines.

C-k with an argument of zero kills the text before point on the current line.

If the variable kill-whole-line is non-nil, C-k at the very beginning of a line kills the entire line including the following newline. This variable is normally nil.

C-S-backspace (kill-whole-line) will kill a whole line including its newline regardless of the position of point within the line. Note that many character terminals will prevent you from typing the key sequence C-S-backspace.

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13.3 Other Kill Commands

Kill region (from point to the mark) (kill-region).
Kill word (kill-word). See Words.
Kill word backwards (backward-kill-word).
C-x <DEL>
Kill back to beginning of sentence (backward-kill-sentence). See Sentences.
Kill to end of sentence (kill-sentence).
Kill the following balanced expression (kill-sexp). See Expressions.
M-z char
Kill through the next occurrence of char (zap-to-char).

The most general kill command is C-w (kill-region), which kills everything between point and the mark. With this command, you can kill any contiguous sequence of characters, if you first set the region around them.

A convenient way of killing is combined with searching: M-z (zap-to-char) reads a character and kills from point up to (and including) the next occurrence of that character in the buffer. A numeric argument acts as a repeat count. A negative argument means to search backward and kill text before point.

Other syntactic units can be killed: words, with M-<DEL> and M-d (see Words); balanced expressions, with C-M-k (see Expressions); and sentences, with C-x <DEL> and M-k (see Sentences).

Previous: Other Kill Commands, Up: Killing

13.4 Killing on Graphical Terminals

On multi-window terminals, the most recent kill done in Emacs is also the primary selection, if it is more recent than any selection you made in another program. This means that the paste commands of other applications with separate windows copy the text that you killed in Emacs. In addition, Emacs yank commands treat other applications' selections as part of the kill ring, so you can yank them into Emacs.

Many window systems follow the convention that insertion while text is selected deletes the selected text. You can make Emacs behave this way by enabling Delete Selection mode, with M-x delete-selection-mode, or using Custom. Another effect of this mode is that <DEL>, C-d and some other keys, when a selection exists, will kill the whole selection. It also enables Transient Mark mode (see Transient Mark).

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14 Yanking

Yanking means reinserting text previously killed. This is what some systems call “pasting.” The usual way to move or copy text is to kill it and then yank it elsewhere one or more times. This is very safe because Emacs remembers many recent kills, not just the last one.

Yank last killed text (yank).
Replace text just yanked with an earlier batch of killed text (yank-pop).
Save region as last killed text without actually killing it (kill-ring-save). Some systems call this “copying”.
Append next kill to last batch of killed text (append-next-kill).

On window systems, if there is a current selection in some other application, and you selected it more recently than you killed any text in Emacs, C-y copies the selection instead of text killed within Emacs.

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14.1 The Kill Ring

All killed text is recorded in the kill ring, a list of blocks of text that have been killed. There is only one kill ring, shared by all buffers, so you can kill text in one buffer and yank it in another buffer. This is the usual way to move text from one file to another. (See Accumulating Text, for some other ways.)

The command C-y (yank) reinserts the text of the most recent kill. It leaves the cursor at the end of the text. It sets the mark at the beginning of the text. See Mark.

C-u C-y leaves the cursor in front of the text, and sets the mark after it. This happens only if the argument is specified with just a C-u, precisely. Any other sort of argument, including C-u and digits, specifies an earlier kill to yank (see Earlier Kills).

The yank commands discard certain text properties from the text that is yanked, those that might lead to annoying results. For instance, they discard text properties that respond to the mouse or specify key bindings. The variable yank-excluded-properties specifies the properties to discard. Yanking of register contents and rectangles also discard these properties.

To copy a block of text, you can use M-w (kill-ring-save), which copies the region into the kill ring without removing it from the buffer. This is approximately equivalent to C-w followed by C-x u, except that M-w does not alter the undo history and does not temporarily change the screen.

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14.2 Appending Kills

Normally, each kill command pushes a new entry onto the kill ring. However, two or more kill commands in a row combine their text into a single entry, so that a single C-y yanks all the text as a unit, just as it was before it was killed.

Thus, if you want to yank text as a unit, you need not kill all of it with one command; you can keep killing line after line, or word after word, until you have killed it all, and you can still get it all back at once.

Commands that kill forward from point add onto the end of the previous killed text. Commands that kill backward from point add text onto the beginning. This way, any sequence of mixed forward and backward kill commands puts all the killed text into one entry without rearrangement. Numeric arguments do not break the sequence of appending kills. For example, suppose the buffer contains this text:

     This is a line -!-of sample text.

with point shown by -!-. If you type M-d M-<DEL> M-d M-<DEL>, killing alternately forward and backward, you end up with ‘a line of sample’ as one entry in the kill ring, and ‘This is text.’ in the buffer. (Note the double space between ‘is’ and ‘text’, which you can clean up with M-<SPC> or M-q.)

Another way to kill the same text is to move back two words with M-b M-b, then kill all four words forward with C-u M-d. This produces exactly the same results in the buffer and in the kill ring. M-f M-f C-u M-<DEL> kills the same text, all going backward; once again, the result is the same. The text in the kill ring entry always has the same order that it had in the buffer before you killed it.

If a kill command is separated from the last kill command by other commands (not just numeric arguments), it starts a new entry on the kill ring. But you can force it to append by first typing the command C-M-w (append-next-kill) right before it. The C-M-w tells the following command, if it is a kill command, to append the text it kills to the last killed text, instead of starting a new entry. With C-M-w, you can kill several separated pieces of text and accumulate them to be yanked back in one place.

A kill command following M-w does not append to the text that M-w copied into the kill ring.

Previous: Appending Kills, Up: Yanking

14.3 Yanking Earlier Kills

To recover killed text that is no longer the most recent kill, use the M-y command (yank-pop). It takes the text previously yanked and replaces it with the text from an earlier kill. So, to recover the text of the next-to-the-last kill, first use C-y to yank the last kill, and then use M-y to replace it with the previous kill. M-y is allowed only after a C-y or another M-y.

You can understand M-y in terms of a “last yank” pointer which points at an entry in the kill ring. Each time you kill, the “last yank” pointer moves to the newly made entry at the front of the ring. C-y yanks the entry which the “last yank” pointer points to. M-y moves the “last yank” pointer to a different entry, and the text in the buffer changes to match. Enough M-y commands can move the pointer to any entry in the ring, so you can get any entry into the buffer. Eventually the pointer reaches the end of the ring; the next M-y loops back around to the first entry again.

M-y moves the “last yank” pointer around the ring, but it does not change the order of the entries in the ring, which always runs from the most recent kill at the front to the oldest one still remembered.

M-y can take a numeric argument, which tells it how many entries to advance the “last yank” pointer by. A negative argument moves the pointer toward the front of the ring; from the front of the ring, it moves “around” to the last entry and continues forward from there.

Once the text you are looking for is brought into the buffer, you can stop doing M-y commands and it will stay there. It's just a copy of the kill ring entry, so editing it in the buffer does not change what's in the ring. As long as no new killing is done, the “last yank” pointer remains at the same place in the kill ring, so repeating C-y will yank another copy of the same previous kill.

If you know how many M-y commands it would take to find the text you want, you can yank that text in one step using C-y with a numeric argument. C-y with an argument restores the text from the specified kill ring entry, counting back from the most recent as 1. Thus, C-u 2 C-y gets the next-to-the-last block of killed text—it is equivalent to C-y M-y. C-y with a numeric argument starts counting from the “last yank” pointer, and sets the “last yank” pointer to the entry that it yanks.

The length of the kill ring is controlled by the variable kill-ring-max; no more than that many blocks of killed text are saved.

The actual contents of the kill ring are stored in a variable named kill-ring; you can view the entire contents of the kill ring with the command C-h v kill-ring.

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15 Accumulating Text

Usually we copy or move text by killing it and yanking it, but there are other convenient methods for copying one block of text in many places, or for copying many scattered blocks of text into one place. To copy one block to many places, store it in a register (see Registers). Here we describe the commands to accumulate scattered pieces of text into a buffer or into a file.

M-x append-to-buffer
Append region to the contents of a specified buffer.
M-x prepend-to-buffer
Prepend region to the contents of a specified buffer.
M-x copy-to-buffer
Copy region into a specified buffer, deleting that buffer's old contents.
M-x insert-buffer
Insert the contents of a specified buffer into current buffer at point.
M-x append-to-file
Append region to the contents of a specified file, at the end.

To accumulate text into a buffer, use M-x append-to-buffer. This reads a buffer name, then inserts a copy of the region into the buffer specified. If you specify a nonexistent buffer, append-to-buffer creates the buffer. The text is inserted wherever point is in that buffer. If you have been using the buffer for editing, the copied text goes into the middle of the text of the buffer, starting from wherever point happens to be at that moment.

Point in that buffer is left at the end of the copied text, so successive uses of append-to-buffer accumulate the text in the specified buffer in the same order as they were copied. Strictly speaking, append-to-buffer does not always append to the text already in the buffer—it appends only if point in that buffer is at the end. However, if append-to-buffer is the only command you use to alter a buffer, then point is always at the end.

M-x prepend-to-buffer is just like append-to-buffer except that point in the other buffer is left before the copied text, so successive prependings add text in reverse order. M-x copy-to-buffer is similar, except that any existing text in the other buffer is deleted, so the buffer is left containing just the text newly copied into it.

To retrieve the accumulated text from another buffer, use the command M-x insert-buffer; this too takes buffername as an argument. It inserts a copy of the whole text in buffer buffername into the current buffer at point, and sets the mark after the inserted text. Alternatively, you can select the other buffer for editing, then copy text from it by killing. See Buffers, for background information on buffers.

Instead of accumulating text within Emacs, in a buffer, you can append text directly into a file with M-x append-to-file, which takes filename as an argument. It adds the text of the region to the end of the specified file. The file is changed immediately on disk.

You should use append-to-file only with files that are not being visited in Emacs. Using it on a file that you are editing in Emacs would change the file behind Emacs's back, which can lead to losing some of your editing.

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16 Rectangles

The rectangle commands operate on rectangular areas of the text: all the characters between a certain pair of columns, in a certain range of lines. Commands are provided to kill rectangles, yank killed rectangles, clear them out, fill them with blanks or text, or delete them. Rectangle commands are useful with text in multicolumn formats, and for changing text into or out of such formats.

When you must specify a rectangle for a command to work on, you do it by putting the mark at one corner and point at the opposite corner. The rectangle thus specified is called the region-rectangle because you control it in much the same way as the region is controlled. But remember that a given combination of point and mark values can be interpreted either as a region or as a rectangle, depending on the command that uses them.

If point and the mark are in the same column, the rectangle they delimit is empty. If they are in the same line, the rectangle is one line high. This asymmetry between lines and columns comes about because point (and likewise the mark) is between two columns, but within a line.

C-x r k
Kill the text of the region-rectangle, saving its contents as the “last killed rectangle” (kill-rectangle).
C-x r d
Delete the text of the region-rectangle (delete-rectangle).
C-x r y
Yank the last killed rectangle with its upper left corner at point (yank-rectangle).
C-x r o
Insert blank space to fill the space of the region-rectangle (open-rectangle). This pushes the previous contents of the region-rectangle rightward.
C-x r c
Clear the region-rectangle by replacing its contents with spaces (clear-rectangle).
M-x delete-whitespace-rectangle
Delete whitespace in each of the lines on the specified rectangle, starting from the left edge column of the rectangle.
C-x r t string <RET>
Replace rectangle contents with string on each line. (string-rectangle).
M-x string-insert-rectangle <RET> string <RET>
Insert string on each line of the rectangle.

The rectangle operations fall into two classes: commands for deleting and inserting rectangles, and commands for blank rectangles.

There are two ways to get rid of the text in a rectangle: you can discard the text (delete it) or save it as the “last killed” rectangle. The commands for these two ways are C-x r d (delete-rectangle) and C-x r k (kill-rectangle). In either case, the portion of each line that falls inside the rectangle's boundaries is deleted, causing any following text on the line to move left into the gap.

Note that “killing” a rectangle is not killing in the usual sense; the rectangle is not stored in the kill ring, but in a special place that can only record the most recent rectangle killed. This is because yanking a rectangle is so different from yanking linear text that different yank commands have to be used and yank-popping is hard to make sense of.

To yank the last killed rectangle, type C-x r y (yank-rectangle). Yanking a rectangle is the opposite of killing one. Point specifies where to put the rectangle's upper left corner. The rectangle's first line is inserted there, the rectangle's second line is inserted at the same horizontal position, but one line vertically down, and so on. The number of lines affected is determined by the height of the saved rectangle.

You can convert single-column lists into double-column lists using rectangle killing and yanking; kill the second half of the list as a rectangle and then yank it beside the first line of the list. See Two-Column, for another way to edit multi-column text.

You can also copy rectangles into and out of registers with C-x r r r and C-x r i r. See Rectangle Registers.

There are two commands you can use for making blank rectangles: C-x r c (clear-rectangle) which blanks out existing text, and C-x r o (open-rectangle) which inserts a blank rectangle. Clearing a rectangle is equivalent to deleting it and then inserting a blank rectangle of the same size.

The command M-x delete-whitespace-rectangle deletes horizontal whitespace starting from a particular column. This applies to each of the lines in the rectangle, and the column is specified by the left edge of the rectangle. The right edge of the rectangle does not make any difference to this command.

The command C-x r t (string-rectangle) replaces the contents of a region-rectangle with a string on each line. The string's width need not be the same as the width of the rectangle. If the string's width is less, the text after the rectangle shifts left; if the string is wider than the rectangle, the text after the rectangle shifts right.

The command M-x string-insert-rectangle is similar to string-rectangle, but inserts the string on each line, shifting the original text to the right.

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17 CUA Bindings

The command M-x cua-mode sets up key bindings that are compatible with the Common User Access (CUA) system used in many other applications. C-x means cut (kill), C-c copy, C-v paste (yank), and C-z undo. Standard Emacs commands like C-x C-c still work, because C-x and C-c only take effect when the mark is active (and the region is highlighted). However, if you don't want these bindings at all, set cua-enable-cua-keys to nil.

In CUA mode, using Shift together with the movement keys activates and highlights the region over which they move. The standard (unshifted) movement keys deactivate the mark, and typed text replaces the active region as in Delete-Selection mode (see Graphical Kill).

To run a command like C-x C-f while the mark is active, use one of the following methods: either hold Shift together with the prefix key, e.g. S-C-x C-f, or quickly type the prefix key twice, e.g. C-x C-x C-f.

CUA mode provides enhanced rectangle support with visible rectangle highlighting. Use C-RET to start a rectangle, extend it using the movement commands, and cut or copy it using C-x or C-c. RET moves the cursor to the next (clockwise) corner of the rectangle, so you can easily expand it in any direction. Normal text you type is inserted to the left or right of each line in the rectangle (on the same side as the cursor).

With CUA you can easily copy text and rectangles into and out of registers by providing a one-digit numeric prefix the the kill, copy, and yank commands, e.g. C-1 C-c copies the region into register 1, and C-2 C-v yanks the contents of register 2.

CUA mode also has a global mark feature which allows easy moving and copying of text between buffers. Use C-S-SPC to toggle the global mark on and off. When the global mark is on, all text that you kill or copy is automatically inserted at the global mark, and text you type is inserted at the global mark rather than at the current position.

For example, to copy words from various buffers into a word list in a given buffer, set the global mark in the target buffer, then navigate to each of the words you want in the list, mark it (e.g. with S-M-f), copy it to the list with C-c or M-w, and insert a newline after the word in the target list by pressing <RET>.

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18 Registers

Emacs registers are compartments where you can save text, rectangles, positions, and other things for later use. Once you save text or a rectangle in a register, you can copy it into the buffer once, or many times; you can move point to a position saved in a register once, or many times.

Each register has a name, which consists of a single character. A register can store a number, a piece of text, a rectangle, a position, a window configuration, or a file name, but only one thing at any given time. Whatever you store in a register remains there until you store something else in that register. To see what a register r contains, use M-x view-register.

M-x view-register <RET> r
Display a description of what register r contains.

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18.1 Saving Positions in Registers

Saving a position records a place in a buffer so that you can move back there later. Moving to a saved position switches to that buffer and moves point to that place in it.

C-x r <SPC> r
Save position of point in register r (point-to-register).
C-x r j r
Jump to the position saved in register r (jump-to-register).

To save the current position of point in a register, choose a name r and type C-x r <SPC> r. The register r retains the position thus saved until you store something else in that register.

The command C-x r j r moves point to the position recorded in register r. The register is not affected; it continues to hold the same position. You can jump to the saved position any number of times.

If you use C-x r j to go to a saved position, but the buffer it was saved from has been killed, C-x r j tries to create the buffer again by visiting the same file. Of course, this works only for buffers that were visiting files.

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18.2 Saving Text in Registers

When you want to insert a copy of the same piece of text several times, it may be inconvenient to yank it from the kill ring, since each subsequent kill moves that entry further down the ring. An alternative is to store the text in a register and later retrieve it.

C-x r s r
Copy region into register r (copy-to-register).
C-x r i r
Insert text from register r (insert-register).
M-x append-to-register <RET> r
Append region to text in register r.
M-x prepend-to-register <RET> r
Prepend region to text in register r.

C-x r s r stores a copy of the text of the region into the register named r. C-u C-x r s r, the same command with a numeric argument, deletes the text from the buffer as well; you can think of this as “moving” the region text into the register.

M-x append-to-register <RET> r appends the copy of the text in the region to the text already stored in the register named r. If invoked with a numeric argument, it deletes the region after appending it to the register. The command prepend-to-register is similar, except that it prepends the region text to the text in the register, rather than appending it.

C-x r i r inserts in the buffer the text from register r. Normally it leaves point before the text and places the mark after, but with a numeric argument (C-u) it puts point after the text and the mark before.

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18.3 Saving Rectangles in Registers

A register can contain a rectangle instead of linear text. The rectangle is represented as a list of strings. See Rectangles, for basic information on how to specify a rectangle in the buffer.

C-x r r r
Copy the region-rectangle into register r (copy-rectangle-to-register). With numeric argument, delete it as well.
C-x r i r
Insert the rectangle stored in register r (if it contains a rectangle) (insert-register).

The C-x r i r command inserts a text string if the register contains one, and inserts a rectangle if the register contains one.

See also the command sort-columns, which you can think of as sorting a rectangle. See Sorting.

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18.4 Saving Window Configurations in Registers

You can save the window configuration of the selected frame in a register, or even the configuration of all windows in all frames, and restore the configuration later.

C-x r w r
Save the state of the selected frame's windows in register r (window-configuration-to-register).
C-x r f r
Save the state of all frames, including all their windows, in register r (frame-configuration-to-register).

Use C-x r j r to restore a window or frame configuration. This is the same command used to restore a cursor position. When you restore a frame configuration, any existing frames not included in the configuration become invisible. If you wish to delete these frames instead, use C-u C-x r j r.

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18.5 Keeping Numbers in Registers

There are commands to store a number in a register, to insert the number in the buffer in decimal, and to increment it. These commands can be useful in keyboard macros (see Keyboard Macros).

C-u number C-x r n r
Store number into register r (number-to-register).
C-u number C-x r + r
Increment the number in register r by number (increment-register).
C-x r i r
Insert the number from register r into the buffer.

C-x r i is the same command used to insert any other sort of register contents into the buffer. C-x r + with no numeric argument increments the register value by 1; C-x r n with no numeric argument stores zero in the register.

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18.6 Keeping File Names in Registers

If you visit certain file names frequently, you can visit them more conveniently if you put their names in registers. Here's the Lisp code used to put a file name in a register:

     (set-register ?r '(file . name))

For example,

     (set-register ?z '(file . "/gd/gnu/emacs/19.0/src/ChangeLog"))

puts the file name shown in register ‘z’.

To visit the file whose name is in register r, type C-x r j r. (This is the same command used to jump to a position or restore a frame configuration.)

Previous: RegFiles, Up: Registers


Bookmarks are somewhat like registers in that they record positions you can jump to. Unlike registers, they have long names, and they persist automatically from one Emacs session to the next. The prototypical use of bookmarks is to record “where you were reading” in various files.

C-x r m <RET>
Set the bookmark for the visited file, at point.
C-x r m bookmark <RET>
Set the bookmark named bookmark at point (bookmark-set).
C-x r b bookmark <RET>
Jump to the bookmark named bookmark (bookmark-jump).
C-x r l
List all bookmarks (list-bookmarks).
M-x bookmark-save
Save all the current bookmark values in the default bookmark file.

The prototypical use for bookmarks is to record one current position in each of several files. So the command C-x r m, which sets a bookmark, uses the visited file name as the default for the bookmark name. If you name each bookmark after the file it points to, then you can conveniently revisit any of those files with C-x r b, and move to the position of the bookmark at the same time.

To display a list of all your bookmarks in a separate buffer, type C-x r l (list-bookmarks). If you switch to that buffer, you can use it to edit your bookmark definitions or annotate the bookmarks. Type C-h m in the bookmark buffer for more information about its special editing commands.

When you kill Emacs, Emacs offers to save your bookmark values in your default bookmark file, ~/.emacs.bmk, if you have changed any bookmark values. You can also save the bookmarks at any time with the M-x bookmark-save command. The bookmark commands load your default bookmark file automatically. This saving and loading is how bookmarks persist from one Emacs session to the next.

If you set the variable bookmark-save-flag to 1, then each command that sets a bookmark will also save your bookmarks; this way, you don't lose any bookmark values even if Emacs crashes. (The value, if a number, says how many bookmark modifications should go by between saving.)

Bookmark position values are saved with surrounding context, so that bookmark-jump can find the proper position even if the file is modified slightly. The variable bookmark-search-size says how many characters of context to record on each side of the bookmark's position.

Here are some additional commands for working with bookmarks:

M-x bookmark-load <RET> filename <RET>
Load a file named filename that contains a list of bookmark values. You can use this command, as well as bookmark-write, to work with other files of bookmark values in addition to your default bookmark file.
M-x bookmark-write <RET> filename <RET>
Save all the current bookmark values in the file filename.
M-x bookmark-delete <RET> bookmark <RET>
Delete the bookmark named bookmark.
M-x bookmark-insert-location <RET> bookmark <RET>
Insert in the buffer the name of the file that bookmark bookmark points to.
M-x bookmark-insert <RET> bookmark <RET>
Insert in the buffer the contents of the file that bookmark bookmark points to.

Next: , Previous: Registers, Up: Top

19 Controlling the Display

Since only part of a large buffer fits in the window, Emacs tries to show a part that is likely to be interesting. Display-control commands allow you to specify which part of the text you want to see, and how to display it.

Next: , Up: Display

19.1 Using Multiple Typefaces

You can specify various styles for displaying text using faces. Each face can specify various face attributes, such as the font family, the height, weight and slant of the characters, the foreground and background color, and underlining or overlining. A face does not have to specify all of these attributes; often it inherits most of them from another face.

On a window system, all the Emacs face attributes are meaningful. On a character terminal, only some of them work. Some character terminals support inverse video, bold, and underline attributes; some support colors. Character terminals generally do not support changing the height and width or the font family.

The easiest way to use faces is to turn on Font Lock mode. See Font Lock, for more information about Font Lock mode and syntactic highlighting. You can print out the buffer with the highlighting that appears on your screen using the command ps-print-buffer-with-faces. See PostScript.

Features which rely on text in multiple faces (such as Font Lock mode) will also work on non-windowed terminals that can display more than one face, whether by colors or underlining and emboldening. This includes the console on GNU/Linux, an xterm which supports colors, the MS-DOS display (see MS-DOS), and the MS-Windows version invoked with the -nw option. Emacs determines automatically whether the terminal has this capability.

You control the appearance of a part of the text in the buffer by specifying the face or faces to use for it. The style of display used for any given character is determined by combining the attributes of all the applicable faces specified for that character. Any attribute that isn't specified by these faces is taken from the default face, whose attributes reflect the default settings of the frame itself.

Enriched mode, the mode for editing formatted text, includes several commands and menus for specifying faces for text in the buffer. See Format Faces, for how to specify the font for text in the buffer. See Format Colors, for how to specify the foreground and background color.

To alter the appearance of a face, use the customization buffer. See Face Customization. You can also use X resources to specify attributes of particular faces (see Resources). Alternatively, you can change the foreground and background colors of a specific face with M-x set-face-foreground and M-x set-face-background. These commands prompt in the minibuffer for a face name and a color name, with completion, and then set that face to use the specified color. Changing the colors of the default face also changes the foreground and background colors on all frames, both existing and those to be created in the future. (You can also set foreground and background colors for the current frame only; see Frame Parameters.)

Emacs can correctly display variable-width fonts, but Emacs commands that calculate width and indentation do not know how to calculate variable widths. This can sometimes lead to incorrect results when you use variable-width fonts. In particular, indentation commands can give inconsistent results, so we recommend you avoid variable-width fonts for editing program source code. Filling will sometimes make lines too long or too short. We plan to address these issues in future Emacs versions.

Next: , Previous: Faces, Up: Display

19.2 Standard Faces

To see what faces are currently defined, and what they look like, type M-x list-faces-display. It's possible for a given face to look different in different frames; this command shows the appearance in the frame in which you type it.

Here are the standard faces for specifying text appearance. You can use them on specific text, when you want the effects they produce.

This face is used for ordinary text that doesn't specify any other face.
This face uses a bold variant of the default font, if it has one. It's up to you to choose a default font that has a bold variant, if you want to use one.
This face uses an italic variant of the default font, if it has one.
This face uses a bold italic variant of the default font, if it has one.
This face underlines text.
This face forces use of a particular fixed-width font.
This face forces use of a particular variable-width font. It's reasonable to customize this to use a different variable-width font, if you like, but you should not make it a fixed-width font.
This face is used for making the text less noticeable than the surrounding ordinary text. Usually this can be achieved by using shades of gray in contrast with either black or white default foreground color.

Here's an incomplete list of faces used to highlight parts of the text temporarily for specific purposes. (Many other modes define their own faces for this purpose.)

This face is used for highlighting portions of text, in various modes. For example, mouse-sensitive text is highlighted using this face.
Like highlight, but used for portions of text on mode lines.
This face is used for highlighting Isearch matches.
This face is used for lazy highlighting of Isearch and Query Replace matches other than the current one.
This face is used for displaying a selected region (when Transient Mark mode is enabled—see below).
This face is used for displaying a secondary X selection (see Secondary Selection).
The face for highlighting excess spaces and tabs at the end of a line when show-trailing-whitespace is non-nil; see Useless Whitespace.
The face for displaying the character “nobreak space”.
The face for highlighting the ‘\’ or ‘^’ that indicates a control character. It's also used when ‘\’ indicates a nobreak space or nobreak (soft) hyphen.

When Transient Mark mode is enabled, the text of the region is highlighted when the mark is active. This uses the face named region; you can control the style of highlighting by changing the style of this face (see Face Customization). See Transient Mark, for more information about Transient Mark mode and activation and deactivation of the mark.

These faces control the appearance of parts of the Emacs frame. They exist as faces to provide a consistent way to customize the appearance of these parts of the frame.

This face is used for the mode line of the currently selected window, and for menu bars when toolkit menus are not used. By default, it's drawn with shadows for a “raised” effect on window systems, and drawn as the inverse of the default face on non-windowed terminals. modeline is an alias for the mode-line face, for compatibility with old Emacs versions.
Like mode-line, but used for mode lines of the windows other than the selected one (if mode-line-in-non-selected-windows is non-nil). This face inherits from mode-line, so changes in that face affect mode lines in all windows.
Similar to mode-line for a window's header line. Most modes don't use the header line, but some special modes, such the Info mode, do.
This face is used for the vertical divider between windows. By default this face inherits from the mode-line-inactive face on character terminals. On window systems the foreground color of this face is used for the vertical line between windows without scrollbars.
This face is used for the prompt strings displayed in the minibuffer. By default, Emacs automatically adds this face to the value of minibuffer-prompt-properties, which is a list of text properties used to display the prompt text.
The face for the fringes to the left and right of windows on graphic displays. (The fringes are the narrow portions of the Emacs frame between the text area and the window's right and left borders.) See Fringes.
This face determines the visual appearance of the scroll bar. See Scroll Bars.
This face determines the color of the frame border.
This face determines the color of the cursor.
This face determines the color of the mouse pointer.
This is the basic tool-bar face. No text appears in the tool bar, but the colors of this face affect the appearance of tool bar icons. See Tool Bars.
This face is used for tooltips. See Tooltips.
This face determines the colors and font of Emacs's menus. See Menu Bars. Setting the font of LessTif/Motif menus is currently not supported; attempts to set the font are ignored in this case. Likewise, attempts to customize this face in Emacs built with GTK and in the MS-Windows port are ignored by the respective GUI toolkits; you need to use system-wide styles and options to change the appearance of the menus.

Next: , Previous: Standard Faces, Up: Display

19.3 Font Lock mode

Font Lock mode is a minor mode, always local to a particular buffer, which highlights (or “fontifies”) the buffer contents according to the syntax of the text you are editing. It can recognize comments and strings in most languages; in several languages, it can also recognize and properly highlight various other important constructs—for example, names of functions being defined or reserved keywords. Some special modes, such as Occur mode and Info mode, have completely specialized ways of assigning fonts for Font Lock mode.

Font Lock mode is turned on by default in all modes which support it. You can toggle font-lock for each buffer with the command M-x font-lock-mode. Using a positive argument unconditionally turns Font Lock mode on, and a negative or zero argument turns it off.

If you do not wish Font Lock mode to be turned on by default, customize the variable global-font-lock-mode using the Customize interface (see Easy Customization), or use the function global-font-lock-mode in your .emacs file, like this:

     (global-font-lock-mode 0)

If you have disabled Global Font Lock mode, you can still enable font lock for specific major modes by adding the function turn-on-font-lock to the mode hooks (see Hooks). For example, to enable Font Lock mode for editing C files, you can do this:

     (add-hook 'c-mode-hook 'turn-on-font-lock)

Font Lock mode uses several specifically named faces to do its job, including font-lock-string-face, font-lock-comment-face, and others. The easiest way to find them all is to use M-x customize-group <RET> font-lock-faces <RET>.

To change the colors or the fonts used by Font Lock mode to fontify different parts of text, just change these faces. There are two ways to do it:

The variable font-lock-maximum-decoration specifies the preferred level of fontification, for modes that provide multiple levels. Level 1 is the least amount of fontification; some modes support levels as high as 3. The normal default is “as high as possible.” You can specify an integer, which applies to all modes, or you can specify different numbers for particular major modes; for example, to use level 1 for C/C++ modes, and the default level otherwise, use this:

     (setq font-lock-maximum-decoration
           '((c-mode . 1) (c++-mode . 1)))

Fontification can be too slow for large buffers, so you can suppress it. The variable font-lock-maximum-size specifies a buffer size, beyond which buffer fontification is suppressed.

Comment and string fontification (or “syntactic” fontification) relies on analysis of the syntactic structure of the buffer text. For the sake of speed, some modes, including C mode and Lisp mode, rely on a special convention: an open-parenthesis or open-brace in the leftmost column always defines the beginning of a defun, and is thus always outside any string or comment. (See Left Margin Paren.) If you don't follow this convention, Font Lock mode can misfontify the text that follows an open-parenthesis or open-brace in the leftmost column that is inside a string or comment.

The variable font-lock-beginning-of-syntax-function (always buffer-local) specifies how Font Lock mode can find a position guaranteed to be outside any comment or string. In modes which use the leftmost column parenthesis convention, the default value of the variable is beginning-of-defun—that tells Font Lock mode to use the convention. If you set this variable to nil, Font Lock no longer relies on the convention. This avoids incorrect results, but the price is that, in some cases, fontification for a changed text must rescan buffer text from the beginning of the buffer. This can considerably slow down redisplay while scrolling, particularly if you are close to the end of a large buffer.

Font Lock highlighting patterns already exist for many modes, but you may want to fontify additional patterns. You can use the function font-lock-add-keywords, to add your own highlighting patterns for a particular mode. For example, to highlight ‘FIXME:’ words in C comments, use this:

      '(("\\<\\(FIXME\\):" 1 font-lock-warning-face t)))

To remove keywords from the font-lock highlighting patterns, use the function font-lock-remove-keywords. See Search-based Fontification, for documentation of the format of this list.

Fontifying large buffers can take a long time. To avoid large delays when a file is visited, Emacs fontifies only the visible portion of a buffer. As you scroll through the buffer, each portion that becomes visible is fontified as soon as it is displayed. The parts of the buffer that are not displayed are fontified “stealthily,” in the background, i.e. when Emacs is idle. You can control this background fontification, also called Just-In-Time (or JIT) Lock, by customizing variables in the customization group ‘jit-lock’. See Specific Customization.

Next: , Previous: Font Lock, Up: Display

19.4 Interactive Highlighting by Matching

It is sometimes useful to temporarily highlight text that matches a certain regular expression. For example, you might wish to see all the references to a certain variable in a program source file, highlight certain parts in a voluminous output of some program, or make certain names stand out in an article.

Use the M-x hi-lock-mode command to turn on a minor mode that allows you to interactively add and remove regular expressions specifying text to be highlighted. Hi Lock mode works like Font Lock mode (see Font Lock), except that it lets you easily add and remove regular expressions while you are editing a buffer. To enable Hi Lock mode for all buffers use M-x global-hi-lock-mode or place (global-hi-lock-mode 1) in your .emacs file.

You control Hi Lock mode with these commands:

C-x w h regexp <RET> face <RET>
Highlight text that matches regexp using face face (highlight-regexp). By using this command more than once, you can highlight various parts of the text in different ways. The highlighting will remain as long as the buffer is loaded. For example, to highlight all occurrences of the word “whim” using the default face (a yellow background) C-x w h whim <RET> <RET>. Any face can be used for highlighting, Hi Lock provides several of its own and these are pre-loaded into a history list. While being prompted for a face use M-p and M-n to cycle through them.
C-x w r regexp <RET>
Unhighlight regexp (unhighlight-regexp). When activated from the menu select the expression to unhighlight from a list. When activated from the keyboard the most recently added expression will be shown. Use M-p to show the next older expression and M-n to select the next newer expression. When the expression to unhighlight appears press <RET> to unhighlight it. The expression can also be typed and completion is available.
C-x w l regexp <RET> face <RET>
Highlight entire lines containing a match for regexp, using face face (highlight-lines-matching-regexp).
C-x w b
Insert all the current highlighting regexp/face pairs into the buffer at point, with comment delimiters to prevent them from changing your program. This key binding runs the hi-lock-write-interactive-patterns command.

These patterns will be read the next time you visit the file while Hi Lock mode is enabled, or whenever you use the M-x hi-lock-find-patterns command.

C-x w i
Re-read regexp/face pairs in the current buffer (hi-lock-write-interactive-patterns). Users familiar with Font Lock keywords might interactively enter patterns (highlight-regexp), write them into the file (hi-lock-write-interactive-patterns), edit them, perhaps including different faces for different parenthesized parts of the match, and finally use this command (hi-lock-write-interactive-patterns) to have Hi Lock highlight them.

This command does nothing if the major mode is a member of the list hi-lock-exclude-modes.

Next: , Previous: Highlight Interactively, Up: Display

19.5 Highlight Changes Mode

Use M-x highlight-changes-mode to enable a minor mode that uses faces (colors, typically) to indicate which parts of the buffer were changed most recently.

Next: , Previous: Highlight Changes, Up: Display

19.6 Scrolling

If a buffer contains text that is too large to fit entirely within a window that is displaying the buffer, Emacs shows a contiguous portion of the text. The portion shown always contains point.

Scrolling means moving text up or down in the window so that different parts of the text are visible. Scrolling forward means that text moves up, and new text appears at the bottom. Scrolling backward moves text down and new text appears at the top.

Scrolling happens automatically if you move point past the bottom or top of the window. You can also explicitly request scrolling with the commands in this section.

Clear screen and redisplay, scrolling the selected window to center point vertically within it (recenter).
Scroll forward (a windowful or a specified number of lines) (scroll-up).
Likewise, scroll forward.
Scroll backward (scroll-down).
Likewise, scroll backward.
arg C-l
Scroll so point is on line arg (recenter).
Scroll heuristically to bring useful information onto the screen (reposition-window).

The most basic scrolling command is C-l (recenter) with no argument. It scrolls the selected window so that point is halfway down from the top of the window. On a text terminal, it also clears the screen and redisplays all windows. That is useful in case the screen is garbled (see Screen Garbled).

To read the buffer a windowful at a time, use C-v (scroll-up) with no argument. This scrolls forward by nearly the whole window height. The effect is to take the two lines at the bottom of the window and put them at the top, followed by nearly a whole windowful of lines that were not previously visible. If point was in the text that scrolled off the top, it ends up at the new top of the window.

M-v (scroll-down) with no argument scrolls backward in a similar way, also with overlap. The number of lines of overlap across a C-v or M-v is controlled by the variable next-screen-context-lines; by default, it is 2. The function keys <NEXT> and <PRIOR>, or <PAGEDOWN> and <PAGEUP>, are equivalent to C-v and M-v.

The commands C-v and M-v with a numeric argument scroll the text in the selected window up or down a few lines. C-v with an argument moves the text and point up, together, that many lines; it brings the same number of new lines into view at the bottom of the window. M-v with numeric argument scrolls the text downward, bringing that many new lines into view at the top of the window. C-v with a negative argument is like M-v and vice versa.

The names of scroll commands are based on the direction that the text moves in the window. Thus, the command to scroll forward is called scroll-up because it moves the text upward on the screen. The keys <PAGEDOWN> and <PAGEUP> derive their names and customary meanings from a different convention that developed elsewhere; hence the strange result that <PAGEDOWN> runs scroll-up.

Some users like the full-screen scroll commands to keep point at the same screen line. To enable this behavior, set the variable scroll-preserve-screen-position to a non-nil value. In this mode, when scrolling shifts point off the screen, or into the scrolling margins, Emacs moves point to keep the same vertical position within the window. This mode is convenient for browsing through a file by scrolling by screenfuls; if you come back to the screen where you started, point goes back to the line where it started. However, this mode is inconvenient when you move to the next screen in order to move point to the text there.

Another way to do scrolling is with C-l with a numeric argument. C-l does not clear the screen when given an argument; it only scrolls the selected window. With a positive argument n, it repositions text to put point n lines down from the top. An argument of zero puts point on the very top line. Point does not move with respect to the text; rather, the text and point move rigidly on the screen. C-l with a negative argument puts point that many lines from the bottom of the window. For example, C-u - 1 C-l puts point on the bottom line, and C-u - 5 C-l puts it five lines from the bottom. C-u C-l scrolls to put point at the center (vertically) of the selected window.

The C-M-l command (reposition-window) scrolls the current window heuristically in a way designed to get useful information onto the screen. For example, in a Lisp file, this command tries to get the entire current defun onto the screen if possible.

Scrolling happens automatically when point moves out of the visible portion of the text. Normally, automatic scrolling centers point vertically within the window. However, if you set scroll-conservatively to a small number n, then if you move point just a little off the screen—less than n lines—then Emacs scrolls the text just far enough to bring point back on screen. By default, scroll-conservatively is 0.

When the window does scroll by a longer distance, you can control how aggressively it scrolls, by setting the variables scroll-up-aggressively and scroll-down-aggressively. The value of scroll-up-aggressively should be either nil, or a fraction f between 0 and 1. A fraction specifies where on the screen to put point when scrolling upward. More precisely, when a window scrolls up because point is above the window start, the new start position is chosen to put point f part of the window height from the top. The larger f, the more aggressive the scrolling.

nil, which is the default, scrolls to put point at the center. So it is equivalent to .5.

Likewise, scroll-down-aggressively is used for scrolling down. The value, f, specifies how far point should be placed from the bottom of the window; thus, as with scroll-up-aggressively, a larger value is more aggressive.

The variable scroll-margin restricts how close point can come to the top or bottom of a window. Its value is a number of screen lines; if point comes within that many lines of the top or bottom of the window, Emacs recenters the window. By default, scroll-margin is 0.

Next: , Previous: Scrolling, Up: Display

19.7 Horizontal Scrolling

Horizontal scrolling means shifting all the lines sideways within a window—so that some of the text near the left margin is not displayed at all. When the text in a window is scrolled horizontally, text lines are truncated rather than continued (see Display Custom). Whenever a window shows truncated lines, Emacs automatically updates its horizontal scrolling whenever point moves off the left or right edge of the screen. You can also use these commands to do explicit horizontal scrolling.

C-x <
Scroll text in current window to the left (scroll-left).
C-x >
Scroll to the right (scroll-right).

The command C-x < (scroll-left) scrolls the selected window to the left by n columns with argument n. This moves part of the beginning of each line off the left edge of the window. With no argument, it scrolls by almost the full width of the window (two columns less, to be precise).

C-x > (scroll-right) scrolls similarly to the right. The window cannot be scrolled any farther to the right once it is displayed normally (with each line starting at the window's left margin); attempting to do so has no effect. This means that you don't have to calculate the argument precisely for C-x >; any sufficiently large argument will restore the normal display.

If you use those commands to scroll a window horizontally, that sets a lower bound for automatic horizontal scrolling. Automatic scrolling will continue to scroll the window, but never farther to the right than the amount you previously set by scroll-left.

The value of the variable hscroll-margin controls how close to the window's edges point is allowed to get before the window will be automatically scrolled. It is measured in columns. If the value is 5, then moving point within 5 columns of the edge causes horizontal scrolling away from that edge.

The variable hscroll-step determines how many columns to scroll the window when point gets too close to the edge. If it's zero, horizontal scrolling centers point horizontally within the window. If it's a positive integer, it specifies the number of columns to scroll by. If it's a floating-point number, it specifies the fraction of the window's width to scroll by. The default is zero.

To disable automatic horizontal scrolling, set the variable auto-hscroll-mode to nil.

Next: , Previous: Horizontal Scrolling, Up: Display

19.8 Window Fringes

On a graphical display, each Emacs window normally has narrow fringes on the left and right edges. The fringes display indications about the text in the window.

The most common use of the fringes is to indicate a continuation line, when one line of text is split into multiple lines on the screen. The left fringe shows a curving arrow for each screen line except the first, indicating that “this is not the real beginning.” The right fringe shows a curving arrow for each screen line except the last, indicating that “this is not the real end.”

The fringes indicate line truncation with short horizontal arrows meaning “there's more text on this line which is scrolled horizontally out of view;” clicking the mouse on one of the arrows scrolls the display horizontally in the direction of the arrow. The fringes can also indicate other things, such as empty lines, or where a program you are debugging is executing (see Debuggers).

You can enable and disable the fringes for all frames using M-x fringe-mode. To enable and disable the fringes for the selected frame, use M-x set-fringe-style.

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19.9 Useless Whitespace

It is easy to leave unnecessary spaces at the end of a line, or empty lines at the end of a file, without realizing it. In most cases, this trailing whitespace has no effect, but there are special circumstances where it matters.

You can make trailing whitespace at the end of a line visible on the screen by setting the buffer-local variable show-trailing-whitespace to t. Then Emacs displays trailing whitespace in the face trailing-whitespace.

This feature does not apply when point is at the end of the line containing the whitespace. Strictly speaking, that is “trailing whitespace” nonetheless, but displaying it specially in that case looks ugly while you are typing in new text. In this special case, the location of point is enough to show you that the spaces are present.

To delete all trailing whitespace within the current buffer's accessible portion (see Narrowing), type M-x delete-trailing-whitespace <RET>. (This command does not remove the form-feed characters.)

Emacs can indicate unused lines at the end of the window with a small image in the left fringe (see Fringes). The image appears for window lines that do not correspond to any buffer text. Blank lines at the end of the buffer then stand out because they do not have this image in the fringe.

To enable this feature, set the buffer-local variable indicate-empty-lines to a non-nil value. The default value of this variable is controlled by the variable default-indicate-empty-lines; by setting that variable, you can enable or disable this feature for all new buffers. (This feature currently doesn't work on character terminals.)

Next: , Previous: Useless Whitespace, Up: Display

19.10 Follow Mode

Follow mode is a minor mode that makes two windows, both showing the same buffer, scroll as a single tall “virtual window.” To use Follow mode, go to a frame with just one window, split it into two side-by-side windows using C-x 3, and then type M-x follow-mode. From then on, you can edit the buffer in either of the two windows, or scroll either one; the other window follows it.

In Follow mode, if you move point outside the portion visible in one window and into the portion visible in the other window, that selects the other window—again, treating the two as if they were parts of one large window.

To turn off Follow mode, type M-x follow-mode a second time.

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19.11 Selective Display

Emacs has the ability to hide lines indented more than a certain number of columns (you specify how many columns). You can use this to get an overview of a part of a program.

To hide lines in the current buffer, type C-x $ (set-selective-display) with a numeric argument n. Then lines with at least n columns of indentation disappear from the screen. The only indication of their presence is that three dots (‘...’) appear at the end of each visible line that is followed by one or more hidden ones.

The commands C-n and C-p move across the hidden lines as if they were not there.

The hidden lines are still present in the buffer, and most editing commands see them as usual, so you may find point in the middle of the hidden text. When this happens, the cursor appears at the end of the previous line, after the three dots. If point is at the end of the visible line, before the newline that ends it, the cursor appears before the three dots.

To make all lines visible again, type C-x $ with no argument.

If you set the variable selective-display-ellipses to nil, the three dots do not appear at the end of a line that precedes hidden lines. Then there is no visible indication of the hidden lines. This variable becomes local automatically when set.

See also Outline Mode for another way to hide part of the text in a buffer.

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19.12 Optional Mode Line Features

The buffer percentage pos indicates the percentage of the buffer above the top of the window. You can additionally display the size of the buffer by typing M-x size-indication-mode to turn on Size Indication mode. The size will be displayed immediately following the buffer percentage like this:

     POS of SIZE

Here SIZE is the human readable representation of the number of characters in the buffer, which means that ‘k’ for 10^3, ‘M’ for 10^6, ‘G’ for 10^9, etc., are used to abbreviate.

If you have narrowed the buffer (see Narrowing), the size of the accessible part of the buffer is shown.

The current line number of point appears in the mode line when Line Number mode is enabled. Use the command M-x line-number-mode to turn this mode on and off; normally it is on. The line number appears after the buffer percentage pos, with the letter ‘L’ to indicate what it is. See Minor Modes, for more information about minor modes and about how to use this command.

If you have narrowed the buffer (see Narrowing), the displayed line number is relative to the accessible portion of the buffer.

If the buffer is very large (larger than the value of line-number-display-limit), then the line number doesn't appear. Emacs doesn't compute the line number when the buffer is large, because that would be too slow. Set it to nil to remove the limit.

Line-number computation can also be slow if the lines in the buffer are too long. For this reason, Emacs normally doesn't display line numbers if the average width, in characters, of lines near point is larger than the value of the variable line-number-display-limit-width. The default value is 200 characters.

You can also display the current column number by turning on Column Number mode. It displays the current column number preceded by the letter ‘C’. Type M-x column-number-mode to toggle this mode.

Emacs can optionally display the time and system load in all mode lines. To enable this feature, type M-x display-time or customize the option display-time-mode. The information added to the mode line usually appears after the buffer name, before the mode names and their parentheses. It looks like this:

     hh:mmpm l.ll

Here hh and mm are the hour and minute, followed always by ‘am’ or ‘pm’. l.ll is the average number of running processes in the whole system recently. (Some fields may be missing if your operating system cannot support them.) If you prefer time display in 24-hour format, set the variable display-time-24hr-format to t.

The word ‘Mail’ appears after the load level if there is mail for you that you have not read yet. On a graphical display you can use an icon instead of ‘Mail’ by customizing display-time-use-mail-icon; this may save some space on the mode line. You can customize display-time-mail-face to make the mail indicator prominent. Use display-time-mail-file to specify the mail file to check, or set display-time-mail-directory to specify the directory to check for incoming mail (any nonempty regular file in the directory is considered as “newly arrived mail”).

By default, the mode line is drawn on graphics displays with 3D-style highlighting, like that of a button when it is not being pressed. If you don't like this effect, you can disable the 3D highlighting of the mode line, by customizing the attributes of the mode-line face in your .emacs init file, like this:

     (set-face-attribute 'mode-line nil :box nil)

Alternatively, you can turn off the box attribute in your .Xdefaults file:

     Emacs.mode-line.AttributeBox: off

By default, the mode line of nonselected windows is displayed in a different face, called mode-line-inactive. Only the selected window is displayed in the mode-line face. This helps show which window is selected. When the minibuffer is selected, since it has no mode line, the window from which you activated the minibuffer has its mode line displayed using mode-line; as a result, ordinary entry to the minibuffer does not change any mode lines.

You can disable use of mode-line-inactive by setting variable mode-line-in-non-selected-windows to nil; then all mode lines are displayed in the mode-line face.

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19.13 How Text Is Displayed

ASCII printing characters (octal codes 040 through 0176) in Emacs buffers are displayed with their graphics, as are non-ASCII multibyte printing characters (octal codes above 0400).

Some ASCII control characters are displayed in special ways. The newline character (octal code 012) is displayed by starting a new line. The tab character (octal code 011) is displayed by moving to the next tab stop column (normally every 8 columns).

Other ASCII control characters are normally displayed as a caret (‘^’) followed by the non-control version of the character; thus, control-A is displayed as ‘^A’.

Non-ASCII characters 0200 through 0237 (octal) are displayed with octal escape sequences; thus, character code 0230 (octal) is displayed as ‘\230’. The display of character codes 0240 through 0377 (octal) may be either as escape sequences or as graphics. They do not normally occur in multibyte buffers, but if they do, they are displayed as Latin-1 graphics. In unibyte mode, if you enable European display they are displayed using their graphics (assuming your terminal supports them), otherwise as escape sequences. See Single-Byte Character Support.

Some character sets define “no-break” versions of the space and hyphen characters, which are used where a line should not be broken. Emacs normally displays these characters with special faces (respectively, nobreak-space and escape-glyph) to distinguish them from ordinary spaces and hyphens. You can turn off this feature by setting the variable nobreak-char-display to nil. If you set the variable to any other value, that means to prefix these characters with an escape character.

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19.14 Displaying the Cursor

You can customize the cursor's color, and whether it blinks, using the cursor Custom group (see Easy Customization). On graphical terminals, the command M-x blink-cursor-mode enables or disables the blinking of the cursor. (On text terminals, the terminal itself blinks the cursor, and Emacs has no control over it.) You can control how the cursor appears when it blinks off by setting the variable blink-cursor-alist.

Normally, the cursor appears in non-selected windows in the “off” state, with the same appearance as when the blinking cursor blinks “off”. For a box cursor, this is a hollow box; for a bar cursor, this is a thinner bar. To turn off cursors in non-selected windows, customize the variable cursor-in-non-selected-windows and assign it a nil value.

On graphical terminals, Emacs can optionally draw the block cursor as wide as the character under the cursor—for example, if the cursor is on a tab character, it would cover the full width occupied by that tab character. To enable this feature, set the variable x-stretch-cursor to a non-nil value.

If you find it hard to see the cursor, you might like HL Line mode, a minor mode that highlights the line containing point. Use M-x hl-line-mode to enable or disable it in the current buffer. M-x global-hl-line-mode enables or disables the same mode globally.

Previous: Cursor Display, Up: Display

19.15 Customization of Display

This section contains information for customization only. Beginning users should skip it.

If the variable inverse-video is non-nil, Emacs attempts to invert all the lines of the display from what they normally are.

If the variable visible-bell is non-nil, Emacs attempts to make the whole screen blink when it would normally make an audible bell sound. This variable has no effect if your terminal does not have a way to make the screen blink.

On a text terminal, when you reenter Emacs after suspending, Emacs normally clears the screen and redraws the entire display. On some terminals with more than one page of memory, it is possible to arrange the termcap entry so that the ‘ti’ and ‘te’ strings (output to the terminal when Emacs is entered and exited, respectively) switch between pages of memory so as to use one page for Emacs and another page for other output. Then you might want to set the variable no-redraw-on-reenter non-nil; this tells Emacs to assume, when resumed, that the screen page it is using still contains what Emacs last wrote there.

The variable echo-keystrokes controls the echoing of multi-character keys; its value is the number of seconds of pause required to cause echoing to start, or zero meaning don't echo at all. See Echo Area.

If the variable ctl-arrow is nil, all control characters in the buffer are displayed with octal escape sequences, except for newline and tab. Altering the value of ctl-arrow makes it local to the current buffer; until that time, the default value is in effect. The default is initially t. See Display Tables.

Normally, a tab character in the buffer is displayed as whitespace which extends to the next display tab stop position, and display tab stops come at intervals equal to eight spaces. The number of spaces per tab is controlled by the variable tab-width, which is made local by changing it, just like ctl-arrow. Note that how the tab character in the buffer is displayed has nothing to do with the definition of <TAB> as a command. The variable tab-width must have an integer value between 1 and 1000, inclusive. The variable default-tab-width controls the default value of this variable for buffers where you have not set it locally.

As an alternative to continuation, Emacs can display long lines by truncation. This means that all the characters that do not fit in the width of the screen or window do not appear at all. On graphical terminals, a small straight arrow in the fringe indicates truncation at either end of the line. On text terminals, ‘$’ appears in the first column when there is text truncated to the left, and in the last column when there is text truncated to the right.

Horizontal scrolling automatically causes line truncation (see Horizontal Scrolling). You can explicitly enable line truncation for a particular buffer with the command M-x toggle-truncate-lines. This works by locally changing the variable truncate-lines. If that variable is non-nil, long lines are truncated; if it is nil, they are continued onto multiple screen lines. Setting the variable truncate-lines in any way makes it local to the current buffer; until that time, the default value is in effect. The default value is normally nil.

If the variable truncate-partial-width-windows is non-nil, it forces truncation rather than continuation in any window less than the full width of the screen or frame, regardless of the value of truncate-lines. For information about side-by-side windows, see Split Window. See also Display.

If the variable overflow-newline-into-fringe is non-nil on a window system, it specifies that lines which are exactly as wide as the window (not counting the final newline character) shall not be broken into two lines on the display (with just the newline on the second line). Instead, the newline overflows into the right fringe, and the cursor will be displayed in the fringe when positioned on that newline.

On a window system, Emacs may indicate the buffer boundaries in the fringes. The buffer boundaries, i.e. first and last line in the buffer, can be marked with angle bitmaps in the left or right fringe. This can be combined with up and down arrow bitmaps shown at the top and bottom of the left or right fringe if the window can be scrolled in either direction.

The buffer-local variable indicate-buffer-boundaries controls how the buffer boundaries and window scrolling is indicated in the fringes.

If the value is left or right, both angle and arrow bitmaps are displayed in the left or right fringe, respectively.

If value is an alist, each element (indicator . position) specifies the position of one of the indicators. The indicator must be one of top, bottom, up, down, or t which specifies the default position for the indicators not present in the alist. The position is one of left, right, or nil which specifies not to show this indicator.

For example, ((top . left) (t . right)) places the top angle bitmap in left fringe, the bottom angle bitmap in right fringe, and both arrow bitmaps in right fringe. To show just the angle bitmaps in the left fringe, but no arrow bitmaps, use ((top . left) (bottom . left)).

The value of the variable default-indicate-buffer-boundaries is the default value for indicate-buffer-boundaries in buffers that do not override it.

The variable baud-rate holds the output speed of the terminal, as far as Emacs knows. Setting this variable does not change the speed of actual data transmission, but the value is used for calculations. On terminals, it affects padding, and decisions about whether to scroll part of the screen or redraw it instead. It also affects the behavior of incremental search.

On window-systems, baud-rate is only used to determine how frequently to look for pending input during display updating. A higher value of baud-rate means that check for pending input will be done less frequently.

You can customize the way any particular character code is displayed by means of a display table. See Display Tables.

On a window system, Emacs can optionally display the mouse pointer in a special shape to say that Emacs is busy. To turn this feature on or off, customize the group cursor. You can also control the amount of time Emacs must remain busy before the busy indicator is displayed, by setting the variable hourglass-delay.

On some text-only terminals, bold face and inverse video together result in text that is hard to read. Call the function tty-suppress-bold-inverse-default-colors with a non-nil argument to suppress the effect of bold-face in this case.

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20 Searching and Replacement

Like other editors, Emacs has commands for searching for occurrences of a string. The principal search command is unusual in that it is incremental; it begins to search before you have finished typing the search string. There are also nonincremental search commands more like those of other editors.

Besides the usual replace-string command that finds all occurrences of one string and replaces them with another, Emacs has a more flexible replacement command called query-replace, which asks interactively which occurrences to replace.

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20.1 Incremental Search

An incremental search begins searching as soon as you type the first character of the search string. As you type in the search string, Emacs shows you where the string (as you have typed it so far) would be found. When you have typed enough characters to identify the place you want, you can stop. Depending on what you plan to do next, you may or may not need to terminate the search explicitly with <RET>.

Incremental search forward (isearch-forward).
Incremental search backward (isearch-backward).

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20.1.1 Basics of Incremental Search

C-s starts a forward incremental search. It reads characters from the keyboard, and moves point past the next occurrence of those characters. If you type C-s and then F, that puts the cursor after the first ‘F’ (the first following the starting point, since this is a forward search). Then if you type an O, you will see the cursor move just after the first ‘FO’ (the ‘F’ in that ‘FO’ may or may not be the first ‘F’). After another O, the cursor moves after the first ‘FOO’ after the place where you started the search. At each step, the buffer text that matches the search string is highlighted, if the terminal can do that; the current search string is always displayed in the echo area.

If you make a mistake in typing the search string, you can cancel characters with <DEL>. Each <DEL> cancels the last character of search string. This does not happen until Emacs is ready to read another input character; first it must either find, or fail to find, the character you want to erase. If you do not want to wait for this to happen, use C-g as described below.

When you are satisfied with the place you have reached, you can type <RET>, which stops searching, leaving the cursor where the search brought it. Also, any command not specially meaningful in searches stops the searching and is then executed. Thus, typing C-a would exit the search and then move to the beginning of the line. <RET> is necessary only if the next command you want to type is a printing character, <DEL>, <RET>, or another character that is special within searches (C-q, C-w, C-r, C-s, C-y, M-y, M-r, M-c, M-e, and some other meta-characters).

When you exit the incremental search, it sets the mark where point was before the search. That is convenient for moving back there. In Transient Mark mode, incremental search sets the mark without activating it, and does so only if the mark is not already active.

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20.1.2 Repeating Incremental Search

Sometimes you search for ‘FOO’ and find one, but not the one you expected to find. There was a second ‘FOO’ that you forgot about, before the one you were aiming for. In this event, type another C-s to move to the next occurrence of the search string. You can repeat this any number of times. If you overshoot, you can cancel some C-s characters with <DEL>.

After you exit a search, you can search for the same string again by typing just C-s C-s: the first C-s is the key that invokes incremental search, and the second C-s means “search again.”

If a search is failing and you ask to repeat it by typing another C-s, it starts again from the beginning of the buffer. Repeating a failing reverse search with C-r starts again from the end. This is called wrapping around, and ‘Wrapped’ appears in the search prompt once this has happened. If you keep on going past the original starting point of the search, it changes to ‘Overwrapped’, which means that you are revisiting matches that you have already seen.

To reuse earlier search strings, use the search ring. The commands M-p and M-n move through the ring to pick a search string to reuse. These commands leave the selected search ring element in the minibuffer, where you can edit it. To edit the current search string in the minibuffer without replacing it with items from the search ring, type M-e. Type C-s or C-r to terminate editing the string and search for it.

You can change to searching backwards with C-r. If a search fails because the place you started was too late in the file, you should do this. Repeated C-r keeps looking for more occurrences backwards. A C-s starts going forwards again. C-r in a search can be canceled with <DEL>.

If you know initially that you want to search backwards, you can use C-r instead of C-s to start the search, because C-r as a key runs a command (isearch-backward) to search backward. A backward search finds matches that are entirely before the starting point, just as a forward search finds matches that begin after it.

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20.1.3 Errors in Incremental Search

If your string is not found at all, the echo area says ‘Failing I-Search’. The cursor is after the place where Emacs found as much of your string as it could. Thus, if you search for ‘FOOT’, and there is no ‘FOOT’, you might see the cursor after the ‘FOO’ in ‘FOOL’. At this point there are several things you can do. If your string was mistyped, you can rub some of it out and correct it. If you like the place you have found, you can type <RET> or some other Emacs command to remain there. Or you can type C-g, which removes from the search string the characters that could not be found (the ‘T’ in ‘FOOT’), leaving those that were found (the ‘FOO’ in ‘FOOT’). A second C-g at that point cancels the search entirely, returning point to where it was when the search started.

The C-g “quit” character does special things during searches; just what it does depends on the status of the search. If the search has found what you specified and is waiting for input, C-g cancels the entire search. The cursor moves back to where you started the search. If C-g is typed when there are characters in the search string that have not been found—because Emacs is still searching for them, or because it has failed to find them—then the search string characters which have not been found are discarded from the search string. With them gone, the search is now successful and waiting for more input, so a second C-g will cancel the entire search.

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20.1.4 Special Input for Incremental Search

An upper-case letter in the search string makes the search case-sensitive. If you delete the upper-case character from the search string, it ceases to have this effect. See Search Case.

To search for a newline, type C-j. To search for another control character, such as control-S or carriage return, you must quote it by typing C-q first. This function of C-q is analogous to its use for insertion (see Inserting Text): it causes the following character to be treated the way any “ordinary” character is treated in the same context. You can also specify a character by its octal code: enter C-q followed by a sequence of octal digits.

M-% typed in incremental search invokes query-replace or query-replace-regexp (depending on search mode) with the current search string used as the string to replace. See Query Replace.

Entering <RET> when the search string is empty launches nonincremental search (see Nonincremental Search).

To customize the special characters that incremental search understands, alter their bindings in the keymap isearch-mode-map. For a list of bindings, look at the documentation of isearch-mode with C-h f isearch-mode <RET>.

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20.1.5 Isearch for Non-ASCII Characters

To enter non-ASCII characters in an incremental search, you must use an input method (see Input Methods). If an input method is enabled in the current buffer when you start the search, you can use it while you type the search string also. Emacs indicates that by including the input method mnemonic in its prompt, like this:

     I-search [im]:

where im is the mnemonic of the active input method. You can toggle (enable or disable) the input method while you type the search string with C-\ (isearch-toggle-input-method). You can turn on a certain (non-default) input method with C-^ (isearch-toggle-specified-input-method), which prompts for the name of the input method. The input method you enable during incremental search remains enabled in the current buffer afterwards.

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20.1.6 Isearch Yanking

The characters C-w and C-y can be used in incremental search to grab text from the buffer into the search string. This makes it convenient to search for another occurrence of text at point. C-w copies the character or word after point as part of the search string, advancing point over it. (The decision, whether to copy a character or a word, is heuristic.) Another C-s to repeat the search will then search for a string including that character or word.

C-y is similar to C-w but copies all the rest of the current line into the search string. If point is already at the end of a line, it grabs the entire next line. Both C-y and C-w convert the text they copy to lower case if the search is currently not case-sensitive; this is so the search remains case-insensitive.

C-M-w and C-M-y modify the search string by only one character at a time: C-M-w deletes the last character from the search string and C-M-y copies the character after point to the end of the search string. An alternative method to add the character after point into the search string is to enter the minibuffer by M-e and to type C-f at the end of the search string in the minibuffer.

The character M-y copies text from the kill ring into the search string. It uses the same text that C-y as a command would yank. Mouse-2 in the echo area does the same. See Yanking.

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20.1.7 Lazy Search Highlighting

When you pause for a little while during incremental search, it highlights all other possible matches for the search string. This makes it easier to anticipate where you can get to by typing C-s or C-r to repeat the search. The short delay before highlighting other matches helps indicate which match is the current one. If you don't like this feature, you can turn it off by setting isearch-lazy-highlight to nil.

You can control how this highlighting looks by customizing the faces isearch (used for the current match) and lazy-highlight (for all the other matches). The latter is also used for other matches inside query-replace.

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20.1.8 Scrolling During Incremental Search

Vertical scrolling during incremental search can be enabled by setting the customizable variable isearch-allow-scroll to a non-nil value.

You can then use the vertical scroll-bar or certain keyboard commands such as <PRIOR> (scroll-down), <NEXT> (scroll-up) and C-l (recenter) within the search, thus letting you see more of the text near the current match. You must run these commands via their key sequences to stay in the search—typing M-x command-name will always terminate a search.

You can give prefix arguments to these commands in the usual way. The current match cannot be scrolled out of the window—this is intentional.

Several other commands, such as C-x 2 (split-window-vertically) and C-x ^ (enlarge-window) which don't scroll the window, are nevertheless made available under this rubric, since they are likewise handy during a search.

You can make other commands usable within an incremental search by giving the command a non-nil isearch-scroll property. For example, to make C-h l usable within an incremental search in all future Emacs sessions, use C-h c to find what command it runs. (You type C-h c C-h l; it says view-lossage.) Then you can put the following line in your .emacs file (see Init File):

     (put 'view-lossage 'isearch-scroll t)

This works for commands that don't permanently change point, the buffer contents, the match data, the current buffer, or the selected window and frame. The command must not delete the current window and must not itself attempt an incremental search.

Previous: Isearch Scroll, Up: Incremental Search

20.1.9 Slow Terminal Incremental Search

Incremental search on a slow terminal uses a modified style of display that is designed to take less time. Instead of redisplaying the buffer at each place the search gets to, it creates a new single-line window and uses that to display the line that the search has found. The single-line window comes into play as soon as point moves outside of the text that is already on the screen.

When you terminate the search, the single-line window is removed. Emacs then redisplays the window in which the search was done, to show its new position of point.

The slow terminal style of display is used when the terminal baud rate is less than or equal to the value of the variable search-slow-speed, initially 1200. See also the discussion of the variable baud-rate (see Customization of Display).

The number of lines to use in slow terminal search display is controlled by the variable search-slow-window-lines. Its normal value is 1.

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20.2 Nonincremental Search

Emacs also has conventional nonincremental search commands, which require you to type the entire search string before searching begins.

C-s <RET> string <RET>
Search for string.
C-r <RET> string <RET>
Search backward for string.

To do a nonincremental search, first type C-s <RET>. This enters the minibuffer to read the search string; terminate the string with <RET>, and then the search takes place. If the string is not found, the search command signals an error.

When you type C-s <RET>, the C-s invokes incremental search as usual. That command is specially programmed to invoke nonincremental search, search-forward, if the string you specify is empty. (Such an empty argument would otherwise be useless.) But it does not call search-forward right away. First it checks the next input character to see if is C-w, which specifies a word search. C-r <RET> does likewise, for a reverse incremental search.

Forward and backward nonincremental searches are implemented by the commands search-forward and search-backward. These commands may be bound to keys in the usual manner. The feature that you can get to them via the incremental search commands exists for historical reasons, and to avoid the need to find key sequences for them.

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20.3 Word Search

Word search searches for a sequence of words without regard to how the words are separated. More precisely, you type a string of many words, using single spaces to separate them, and the string can be found even if there are multiple spaces, newlines, or other punctuation characters between these words.

Word search is useful for editing a printed document made with a text formatter. If you edit while looking at the printed, formatted version, you can't tell where the line breaks are in the source file. With word search, you can search without having to know them.

C-s <RET> C-w words <RET>
Search for words, ignoring details of punctuation.
C-r <RET> C-w words <RET>
Search backward for words, ignoring details of punctuation.

Word search is a special case of nonincremental search and is invoked with C-s <RET> C-w. This is followed by the search string, which must always be terminated with <RET>. Being nonincremental, this search does not start until the argument is terminated. It works by constructing a regular expression and searching for that; see Regexp Search.

Use C-r <RET> C-w to do backward word search.

Forward and backward word searches are implemented by the commands word-search-forward and word-search-backward. These commands may be bound to keys in the usual manner. They are available via the incremental search commands both for historical reasons and to avoid the need to find suitable key sequences for them.

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20.4 Regular Expression Search

A regular expression (regexp, for short) is a pattern that denotes a class of alternative strings to match, possibly infinitely many. GNU Emacs provides both incremental and nonincremental ways to search for a match for a regexp. The syntax of regular expressions is explained in the following section.

Incremental search for a regexp is done by typing C-M-s (isearch-forward-regexp), by invoking C-s with a prefix argument (whose value does not matter), or by typing M-r within a forward incremental search. This command reads a search string incrementally just like C-s, but it treats the search string as a regexp rather than looking for an exact match against the text in the buffer. Each time you add text to the search string, you make the regexp longer, and the new regexp is searched for. To search backward for a regexp, use C-M-r (isearch-backward-regexp), C-r with a prefix argument, or M-r within a backward incremental search.

All of the control characters that do special things within an ordinary incremental search have the same function in incremental regexp search. Typing C-s or C-r immediately after starting the search retrieves the last incremental search regexp used; that is to say, incremental regexp and non-regexp searches have independent defaults. They also have separate search rings that you can access with M-p and M-n.

If you type <SPC> in incremental regexp search, it matches any sequence of whitespace characters, including newlines. If you want to match just a space, type C-q <SPC>. You can control what a bare spece matches by setting the variable search-whitespace-regexp to the desired regexp.

Note that adding characters to the regexp in an incremental regexp search can make the cursor move back and start again. For example, if you have searched for ‘foo’ and you add ‘\|bar’, the cursor backs up in case the first ‘bar’ precedes the first ‘foo’.

Nonincremental search for a regexp is done by the functions re-search-forward and re-search-backward. You can invoke these with M-x, or bind them to keys, or invoke them by way of incremental regexp search with C-M-s <RET> and C-M-r <RET>.

If you use the incremental regexp search commands with a prefix argument, they perform ordinary string search, like isearch-forward and isearch-backward. See Incremental Search.

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20.5 Syntax of Regular Expressions

This manual describes regular expression features that users typically want to use. There are additional features that are mainly used in Lisp programs; see Regular Expressions.

Regular expressions have a syntax in which a few characters are special constructs and the rest are ordinary. An ordinary character is a simple regular expression which matches that same character and nothing else. The special characters are ‘$’, ‘^’, ‘.’, ‘*’, ‘+’, ‘?’, ‘[’, ‘]’ and ‘\’. Any other character appearing in a regular expression is ordinary, unless a ‘\’ precedes it. (When you use regular expressions in a Lisp program, each ‘\’ must be doubled, see the example near the end of this section.)

For example, ‘f’ is not a special character, so it is ordinary, and therefore ‘f’ is a regular expression that matches the string ‘f’ and no other string. (It does not match the string ‘ff’.) Likewise, ‘o’ is a regular expression that matches only ‘o’. (When case distinctions are being ignored, these regexps also match ‘F’ and ‘O’, but we consider this a generalization of “the same string,” rather than an exception.)

Any two regular expressions a and b can be concatenated. The result is a regular expression which matches a string if a matches some amount of the beginning of that string and b matches the rest of the string.

As a simple example, we can concatenate the regular expressions ‘f’ and ‘o’ to get the regular expression ‘fo’, which matches only the string ‘fo’. Still trivial. To do something nontrivial, you need to use one of the special characters. Here is a list of them.

. (Period)
is a special character that matches any single character except a newline. Using concatenation, we can make regular expressions like ‘a.b’, which matches any three-character string that begins with ‘a’ and ends with ‘b’.
is not a construct by itself; it is a postfix operator that means to match the preceding regular expression repetitively as many times as possible. Thus, ‘o*’ matches any number of ‘o’s (including no ‘o’s).

*’ always applies to the smallest possible preceding expression. Thus, ‘fo*’ has a repeating ‘o’, not a repeating ‘fo’. It matches ‘f’, ‘fo’, ‘foo’, and so on.

The matcher processes a ‘*’ construct by matching, immediately, as many repetitions as can be found. Then it continues with the rest of the pattern. If that fails, backtracking occurs, discarding some of the matches of the ‘*’-modified construct in case that makes it possible to match the rest of the pattern. For example, in matching ‘ca*ar’ against the string ‘caaar’, the ‘a*’ first tries to match all three ‘a’s; but the rest of the pattern is ‘ar’ and there is only ‘r’ left to match, so this try fails. The next alternative is for ‘a*’ to match only two ‘a’s. With this choice, the rest of the regexp matches successfully.

is a postfix operator, similar to ‘*’ except that it must match the preceding expression at least once. So, for example, ‘ca+r’ matches the strings ‘car’ and ‘caaaar’ but not the string ‘cr’, whereas ‘ca*r’ matches all three strings.
is a postfix operator, similar to ‘*’ except that it can match the preceding expression either once or not at all. For example, ‘ca?r’ matches ‘car’ or ‘cr’; nothing else.
*?, +?, ??
are non-greedy variants of the operators above. The normal operators ‘*’, ‘+’, ‘?’ are greedy in that they match as much as they can, as long as the overall regexp can still match. With a following ‘?’, they are non-greedy: they will match as little as possible.

Thus, both ‘ab*’ and ‘ab*?’ can match the string ‘a’ and the string ‘abbbb’; but if you try to match them both against the text ‘abbb’, ‘ab*’ will match it all (the longest valid match), while ‘ab*?’ will match just ‘a’ (the shortest valid match).

Non-greedy operators match the shortest possible string starting at a given starting point; in a forward search, though, the earliest possible starting point for match is always the one chosen. Thus, if you search for ‘a.*?$’ against the text ‘abbab’ followed by a newline, it matches the whole string. Since it can match starting at the first ‘a’, it does.

is a postfix operator that specifies repetition n times—that is, the preceding regular expression must match exactly n times in a row. For example, ‘x\{4\}’ matches the string ‘xxxx’ and nothing else.
is a postfix operator that specifies repetition between n and m times—that is, the preceding regular expression must match at least n times, but no more than m times. If m is omitted, then there is no upper limit, but the preceding regular expression must match at least n times.
\{0,1\}’ is equivalent to ‘?’.
\{0,\}’ is equivalent to ‘*’.
\{1,\}’ is equivalent to ‘+’.
[ ... ]
is a character set, which begins with ‘[’ and is terminated by ‘]’. In the simplest case, the characters between the two brackets are what this set can match.

Thus, ‘[ad]’ matches either one ‘a’ or one ‘d’, and ‘[ad]*’ matches any string composed of just ‘a’s and ‘d’s (including the empty string), from which it follows that ‘c[ad]*r’ matches ‘cr’, ‘car’, ‘cdr’, ‘caddaar’, etc.

You can also include character ranges in a character set, by writing the starting and ending characters with a ‘-’ between them. Thus, ‘[a-z]’ matches any lower-case ASCII letter. Ranges may be intermixed freely with individual characters, as in ‘[a-z$%.]’, which matches any lower-case ASCII letter or ‘$’, ‘%’ or period.

Note that the usual regexp special characters are not special inside a character set. A completely different set of special characters exists inside character sets: ‘]’, ‘-’ and ‘^’.

To include a ‘]’ in a character set, you must make it the first character. For example, ‘[]a]’ matches ‘]’ or ‘a’. To include a ‘-’, write ‘-’ as the first or last character of the set, or put it after a range. Thus, ‘[]-]’ matches both ‘]’ and ‘-’.

To include ‘^’ in a set, put it anywhere but at the beginning of the set. (At the beginning, it complements the set—see below.)

When you use a range in case-insensitive search, you should write both ends of the range in upper case, or both in lower case, or both should be non-letters. The behavior of a mixed-case range such as ‘A-z’ is somewhat ill-defined, and it may change in future Emacs versions.

[^ ... ]
[^’ begins a complemented character set, which matches any character except the ones specified. Thus, ‘[^a-z0-9A-Z]’ matches all characters except ASCII letters and digits.

^’ is not special in a character set unless it is the first character. The character following the ‘^’ is treated as if it were first (in other words, ‘-’ and ‘]’ are not special there).

A complemented character set can match a newline, unless newline is mentioned as one of the characters not to match. This is in contrast to the handling of regexps in programs such as grep.

is a special character that matches the empty string, but only at the beginning of a line in the text being matched. Otherwise it fails to match anything. Thus, ‘^foo’ matches a ‘foo’ that occurs at the beginning of a line.

For historical compatibility reasons, ‘^’ can be used with this meaning only at the beginning of the regular expression, or after ‘\(’ or ‘\|’.

is similar to ‘^’ but matches only at the end of a line. Thus, ‘x+$’ matches a string of one ‘x’ or more at the end of a line.

For historical compatibility reasons, ‘$’ can be used with this meaning only at the end of the regular expression, or before ‘\)’ or ‘\|’.

has two functions: it quotes the special characters (including ‘\’), and it introduces additional special constructs.

Because ‘\’ quotes special characters, ‘\$’ is a regular expression that matches only ‘$’, and ‘\[’ is a regular expression that matches only ‘[’, and so on.

See the following section for the special constructs that begin with ‘\’.

Note: for historical compatibility, special characters are treated as ordinary ones if they are in contexts where their special meanings make no sense. For example, ‘*foo’ treats ‘*’ as ordinary since there is no preceding expression on which the ‘*’ can act. It is poor practice to depend on this behavior; it is better to quote the special character anyway, regardless of where it appears.

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20.6 Backslash in Regular Expressions

For the most part, ‘\’ followed by any character matches only that character. However, there are several exceptions: two-character sequences starting with ‘\’ that have special meanings. The second character in the sequence is always an ordinary character when used on its own. Here is a table of ‘\’ constructs.

specifies an alternative. Two regular expressions a and b with ‘\|’ in between form an expression that matches some text if either a matches it or b matches it. It works by trying to match a, and if that fails, by trying to match b.

Thus, ‘foo\|bar’ matches either ‘foo’ or ‘bar’ but no other string.

\|’ applies to the largest possible surrounding expressions. Only a surrounding ‘\( ... \)’ grouping can limit the grouping power of ‘\|’.

Full backtracking capability exists to handle multiple uses of ‘\|’.

\( ... \)
is a grouping construct that serves three purposes:
  1. To enclose a set of ‘\|’ alternatives for other operations. Thus, ‘\(foo\|bar\)x’ matches either ‘foox’ or ‘barx’.
  2. To enclose a complicated expression for the postfix operators ‘*’, ‘+’ and ‘?’ to operate on. Thus, ‘ba\(na\)*’ matches ‘bananana’, etc., with any (zero or more) number of ‘na’ strings.
  3. To record a matched substring for future reference.

This last application is not a consequence of the idea of a parenthetical grouping; it is a separate feature that is assigned as a second meaning to the same ‘\( ... \)’ construct. In practice there is usually no conflict between the two meanings; when there is a conflict, you can use a “shy” group.

\(?: ... \)
specifies a “shy” group that does not record the matched substring; you can't refer back to it with ‘\d’. This is useful in mechanically combining regular expressions, so that you can add groups for syntactic purposes without interfering with the numbering of the groups that were written by the user.
matches the same text that matched the dth occurrence of a ‘\( ... \)’ construct.

After the end of a ‘\( ... \)’ construct, the matcher remembers the beginning and end of the text matched by that construct. Then, later on in the regular expression, you can use ‘\’ followed by the digit d to mean “match the same text matched the dth time by the ‘\( ... \)’ construct.”

The strings matching the first nine ‘\( ... \)’ constructs appearing in a regular expression are assigned numbers 1 through 9 in the order that the open-parentheses appear in the regular expression. So you can use ‘\1’ through ‘\9’ to refer to the text matched by the corresponding ‘\( ... \)’ constructs.

For example, ‘\(.*\)\1’ matches any newline-free string that is composed of two identical halves. The ‘\(.*\)’ matches the first half, which may be anything, but the ‘\1’ that follows must match the same exact text.

If a particular ‘\( ... \)’ construct matches more than once (which can easily happen if it is followed by ‘*’), only the last match is recorded.

matches the empty string, but only at the beginning of the string or buffer (or its accessible portion) being matched against.
matches the empty string, but only at the end of the string or buffer (or its accessible portion) being matched against.
matches the empty string, but only at point.
matches the empty string, but only at the beginning or end of a word. Thus, ‘\bfoo\b’ matches any occurrence of ‘foo’ as a separate word. ‘\bballs?\b’ matches ‘ball’ or ‘balls’ as a separate word.

\b’ matches at the beginning or end of the buffer regardless of what text appears next to it.

matches the empty string, but not at the beginning or end of a word.
matches the empty string, but only at the beginning of a word. ‘\<’ matches at the beginning of the buffer only if a word-constituent character follows.
matches the empty string, but only at the end of a word. ‘\>’ matches at the end of the buffer only if the contents end with a word-constituent character.
matches any word-constituent character. The syntax table determines which characters these are. See Syntax.
matches any character that is not a word-constituent.
matches the empty string, but only at the beginning of a symbol. A symbol is a sequence of one or more symbol-constituent characters. A symbol-constituent character is a character whose syntax is either ‘w’ or ‘_’. ‘\_<’ matches at the beginning of the buffer only if a symbol-constituent character follows.
matches the empty string, but only at the end of a symbol. ‘\_>’ matches at the end of the buffer only if the contents end with a symbol-constituent character.
matches any character whose syntax is c. Here c is a character that designates a particular syntax class: thus, ‘w’ for word constituent, ‘-’ or ‘ ’ for whitespace, ‘.’ for ordinary punctuation, etc. See Syntax.
matches any character whose syntax is not c.

matches any character that belongs to the category c. For example, ‘\cc’ matches Chinese characters, ‘\cg’ matches Greek characters, etc. For the description of the known categories, type M-x describe-categories <RET>.
matches any character that does not belong to category c.

The constructs that pertain to words and syntax are controlled by the setting of the syntax table (see Syntax).

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20.7 Regular Expression Example

Here is a complicated regexp—a simplified version of the regexp that Emacs uses, by default, to recognize the end of a sentence together with any whitespace that follows. We show its Lisp syntax to distinguish the spaces from the tab characters. In Lisp syntax, the string constant begins and ends with a double-quote. ‘\"’ stands for a double-quote as part of the regexp, ‘\\’ for a backslash as part of the regexp, ‘\t’ for a tab, and ‘\n’ for a newline.

     "[.?!][]\"')]*\\($\\| $\\|\t\\|  \\)[ \t\n]*"

This contains four parts in succession: a character set matching period, ‘?’, or ‘!’; a character set matching close-brackets, quotes, or parentheses, repeated zero or more times; a set of alternatives within backslash-parentheses that matches either end-of-line, a space at the end of a line, a tab, or two spaces; and a character set matching whitespace characters, repeated any number of times.

To enter the same regexp in incremental search, you would type <TAB> to enter a tab, and C-j to enter a newline. You would also type single backslashes as themselves, instead of doubling them for Lisp syntax. In commands that use ordinary minibuffer input to read a regexp, you would quote the C-j by preceding it with a C-q to prevent C-j from exiting the minibuffer.

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20.8 Searching and Case

Incremental searches in Emacs normally ignore the case of the text they are searching through, if you specify the text in lower case. Thus, if you specify searching for ‘foo’, then ‘Foo’ and ‘foo’ are also considered a match. Regexps, and in particular character sets, are included: ‘[ab]’ would match ‘a’ or ‘A’ or ‘b’ or ‘B’.

An upper-case letter anywhere in the incremental search string makes the search case-sensitive. Thus, searching for ‘Foo’ does not find ‘foo’ or ‘FOO’. This applies to regular expression search as well as to string search. The effect ceases if you delete the upper-case letter from the search string.

Typing M-c within an incremental search toggles the case sensitivity of that search. The effect does not extend beyond the current incremental search to the next one, but it does override the effect of including an upper-case letter in the current search.

If you set the variable case-fold-search to nil, then all letters must match exactly, including case. This is a per-buffer variable; altering the variable affects only the current buffer, but there is a default value in default-case-fold-search that you can also set. See Locals. This variable applies to nonincremental searches also, including those performed by the replace commands (see Replace) and the minibuffer history matching commands (see Minibuffer History).

Several related variables control case-sensitivity of searching and matching for specific commands or activities. For instance, tags-case-fold-search controls case sensitivity for find-tag. To find these variables, do M-x apropos-variable <RET> case-fold-search <RET>.

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20.9 Replacement Commands

Global search-and-replace operations are not needed often in Emacs, but they are available. In addition to the simple M-x replace-string command which replaces all occurrences, there is M-% (query-replace), which presents each occurrence of the pattern and asks you whether to replace it.

The replace commands normally operate on the text from point to the end of the buffer; however, in Transient Mark mode (see Transient Mark), when the mark is active, they operate on the region. The replace commands all replace one string (or regexp) with one replacement string. It is possible to perform several replacements in parallel using the command expand-region-abbrevs (see Expanding Abbrevs).

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20.9.1 Unconditional Replacement

M-x replace-string <RET> string <RET> newstring <RET>
Replace every occurrence of string with newstring.

To replace every instance of ‘foo’ after point with ‘bar’, use the command M-x replace-string with the two arguments ‘foo’ and ‘bar’. Replacement happens only in the text after point, so if you want to cover the whole buffer you must go to the beginning first. All occurrences up to the end of the buffer are replaced; to limit replacement to part of the buffer, narrow to that part of the buffer before doing the replacement (see Narrowing). In Transient Mark mode, when the region is active, replacement is limited to the region (see Transient Mark).

When replace-string exits, it leaves point at the last occurrence replaced. It sets the mark to the prior position of point (where the replace-string command was issued); use C-u C-<SPC> to move back there.

A numeric argument restricts replacement to matches that are surrounded by word boundaries. The argument's value doesn't matter.

What if you want to exchange ‘x’ and ‘y’: replace every ‘x’ with a ‘y’ and vice versa? You can do it this way:

     M-x replace-string <RET> x <RET> @TEMP@ <RET>
     M-< M-x replace-string <RET> y <RET> x <RET>
     M-< M-x replace-string <RET> @TEMP@ <RET> y <RET>

This works provided the string ‘@TEMP@’ does not appear in your text.

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20.9.2 Regexp Replacement

The M-x replace-string command replaces exact matches for a single string. The similar command M-x replace-regexp replaces any match for a specified pattern.

M-x replace-regexp <RET> regexp <RET> newstring <RET>
Replace every match for regexp with newstring.

In replace-regexp, the newstring need not be constant: it can refer to all or part of what is matched by the regexp. ‘\&’ in newstring stands for the entire match being replaced. ‘\d’ in newstring, where d is a digit, stands for whatever matched the dth parenthesized grouping in regexp. ‘\#’ refers to the count of replacements already made in this command, as a decimal number. In the first replacement, ‘\#’ stands for ‘0’; in the second, for ‘1’; and so on. For example,

     M-x replace-regexp <RET> c[ad]+r <RET> \&-safe <RET>

replaces (for example) ‘cadr’ with ‘cadr-safe’ and ‘cddr’ with ‘cddr-safe’.

     M-x replace-regexp <RET> \(c[ad]+r\)-safe <RET> \1 <RET>

performs the inverse transformation. To include a ‘\’ in the text to replace with, you must enter ‘\\’.

If you want to enter part of the replacement string by hand each time, use ‘\?’ in the replacement string. Each replacement will ask you to edit the replacement string in the minibuffer, putting point where the ‘\?’ was.

The remainder of this subsection is intended for specialized tasks and requires knowledge of Lisp. Most readers can skip it.

You can use Lisp expressions to calculate parts of the replacement string. To do this, write ‘\,’ followed by the expression in the replacement string. Each replacement calculates the value of the expression and converts it to text without quoting (if it's a string, this means using the string's contents), and uses it in the replacement string in place of the expression itself. If the expression is a symbol, one space in the replacement string after the symbol name goes with the symbol name, so the value replaces them both.

Inside such an expression, you can use some special sequences. ‘\&’ and ‘\n’ refer here, as usual, to the entire match as a string, and to a submatch as a string. n may be multiple digits, and the value of ‘\n’ is nil if subexpression n did not match. You can also use ‘\#&’ and ‘\#n’ to refer to those matches as numbers (this is valid when the match or submatch has the form of a numeral). ‘\#’ here too stands for the number of already-completed replacements.

Repeating our example to exchange ‘x’ and ‘y’, we can thus do it also this way:

     M-x replace-regexp <RET> \(x\)\|y <RET>
     \,(if \1 "y" "x") <RET>

For computing replacement strings for ‘\,’, the format function is often useful (see Formatting Strings). For example, to add consecutively numbered strings like ‘ABC00042’ to columns 73 to 80 (unless they are already occupied), you can use

     M-x replace-regexp <RET> ^.\{0,72\}$ <RET>
     \,(format "%-72sABC%05d" \& \#) <RET>

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20.9.3 Replace Commands and Case

If the first argument of a replace command is all lower case, the command ignores case while searching for occurrences to replace—provided case-fold-search is non-nil. If case-fold-search is set to nil, case is always significant in all searches.

In addition, when the newstring argument is all or partly lower case, replacement commands try to preserve the case pattern of each occurrence. Thus, the command

     M-x replace-string <RET> foo <RET> bar <RET>

replaces a lower case ‘foo’ with a lower case ‘bar’, an all-caps ‘FOO’ with ‘BAR’, and a capitalized ‘Foo’ with ‘Bar’. (These three alternatives—lower case, all caps, and capitalized, are the only ones that replace-string can distinguish.)

If upper-case letters are used in the replacement string, they remain upper case every time that text is inserted. If upper-case letters are used in the first argument, the second argument is always substituted exactly as given, with no case conversion. Likewise, if either case-replace or case-fold-search is set to nil, replacement is done without case conversion.

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20.9.4 Query Replace

M-% string <RET> newstring <RET>
M-x query-replace <RET> string <RET> newstring <RET>
Replace some occurrences of string with newstring.
C-M-% regexp <RET> newstring <RET>
M-x query-replace-regexp <RET> regexp <RET> newstring <RET>
Replace some matches for regexp with newstring.

If you want to change only some of the occurrences of ‘foo’ to ‘bar’, not all of them, then you cannot use an ordinary replace-string. Instead, use M-% (query-replace). This command finds occurrences of ‘foo’ one by one, displays each occurrence and asks you whether to replace it. Aside from querying, query-replace works just like replace-string. It preserves case, like replace-string, provided case-replace is non-nil, as it normally is. A numeric argument means consider only occurrences that are bounded by word-delimiter characters.

C-M-% performs regexp search and replace (query-replace-regexp). It works like replace-regexp except that it queries like query-replace.

These commands highlight the current match using the face query-replace. They highlight other matches using lazy-highlight just like incremental search (see Incremental Search).

The characters you can type when you are shown a match for the string or regexp are:

to replace the occurrence with newstring.
to skip to the next occurrence without replacing this one.
, (Comma)
to replace this occurrence and display the result. You are then asked for another input character to say what to do next. Since the replacement has already been made, <DEL> and <SPC> are equivalent in this situation; both move to the next occurrence.

You can type C-r at this point (see below) to alter the replaced text. You can also type C-x u to undo the replacement; this exits the query-replace, so if you want to do further replacement you must use C-x <ESC> <ESC> <RET> to restart (see Repetition).

to exit without doing any more replacements.
. (Period)
to replace this occurrence and then exit without searching for more occurrences.
to replace all remaining occurrences without asking again.
to go back to the position of the previous occurrence (or what used to be an occurrence), in case you changed it by mistake or want to reexamine it.
to enter a recursive editing level, in case the occurrence needs to be edited rather than just replaced with newstring. When you are done, exit the recursive editing level with C-M-c to proceed to the next occurrence. See Recursive Edit.
to delete the occurrence, and then enter a recursive editing level as in C-r. Use the recursive edit to insert text to replace the deleted occurrence of string. When done, exit the recursive editing level with C-M-c to proceed to the next occurrence.
to edit the replacement string in the minibuffer. When you exit the minibuffer by typing <RET>, the minibuffer contents replace the current occurrence of the pattern. They also become the new replacement string for any further occurrences.
to redisplay the screen. Then you must type another character to specify what to do with this occurrence.
to display a message summarizing these options. Then you must type another character to specify what to do with this occurrence.

Some other characters are aliases for the ones listed above: y, n and q are equivalent to <SPC>, <DEL> and <RET>.

Aside from this, any other character exits the query-replace, and is then reread as part of a key sequence. Thus, if you type C-k, it exits the query-replace and then kills to end of line.

To restart a query-replace once it is exited, use C-x <ESC> <ESC>, which repeats the query-replace because it used the minibuffer to read its arguments. See C-x ESC ESC.

See also Transforming File Names, for Dired commands to rename, copy, or link files by replacing regexp matches in file names.

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20.10 Other Search-and-Loop Commands

Here are some other commands that find matches for a regular expression. They all ignore case in matching, if the pattern contains no upper-case letters and case-fold-search is non-nil. Aside from occur and its variants, all operate on the text from point to the end of the buffer, or on the active region in Transient Mark mode.

M-x occur <RET> regexp <RET>
Display a list showing each line in the buffer that contains a match for regexp. To limit the search to part of the buffer, narrow to that part (see Narrowing). A numeric argument n specifies that n lines of context are to be displayed before and after each matching line. Currently, occur can not correctly handle multiline matches.

The buffer ‘*Occur*’ containing the output serves as a menu for finding the occurrences in their original context. Click Mouse-2 on an occurrence listed in ‘*Occur*’, or position point there and type <RET>; this switches to the buffer that was searched and moves point to the original of the chosen occurrence. o and C-o display the match in another window; C-o does not select it.

Occur mode supports the next-error functionality described in Compilation Mode.

M-x list-matching-lines
Synonym for M-x occur.
M-x multi-occur <RET> buffers <RET> regexp <RET>
This function is just like occur, except it is able to search through multiple buffers.
M-x multi-occur-by-filename-regexp <RET> bufregexp <RET> regexp <RET>
This function is similar to multi-occur, except the buffers to search are specified by a regexp on their filename.
M-x how-many <RET> regexp <RET>
Print the number of matches for regexp that exist in the buffer after point. In Transient Mark mode, if the region is active, the command operates on the region instead.
M-x flush-lines <RET> regexp <RET>
This command deletes each line that contains a match for regexp, operating on the text after point; it deletes the current line if it contains a match starting after point. In Transient Mark mode, if the region is active, the command operates on the region instead; it deletes a line partially contained in the region if it contains a match entirely contained in the region.

If a match is split across lines, flush-lines deletes all those lines. It deletes the lines before starting to look for the next match; hence, it ignores a match starting on the same line at which another match ended.

M-x keep-lines <RET> regexp <RET>
This command deletes each line that does not contain a match for regexp, operating on the text after point; if point is not at the beginning of a line, it always keeps the current line. In Transient Mark mode, if the region is active, the command operates on the region instead; it never deletes lines that are only partially contained in the region (a newline that ends a line counts as part of that line).

If a match is split across lines, this command keeps all those lines.

You can also search multiple files under control of a tags table (see Tags Search) or through the Dired A command (see Operating on Files), or ask the grep program to do it (see Grep Searching).

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21 Commands for Fixing Typos

In this chapter we describe the commands that are especially useful for the times when you catch a mistake in your text just after you have made it, or change your mind while composing text on the fly.

The most fundamental command for correcting erroneous editing is the undo command, C-x u or C-_ or C-/. This command undoes a single command (usually), a part of a command (in the case of query-replace), or several consecutive self-inserting characters. Consecutive repetitions of the undo command undo earlier and earlier changes, back to the limit of the undo information available. See Undo, for more information.

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21.1 Killing Your Mistakes

Delete last character (delete-backward-char).
Kill last word (backward-kill-word).
C-x <DEL>
Kill to beginning of sentence (backward-kill-sentence).

The <DEL> character (delete-backward-char) is the most important correction command. It deletes the character before point. When <DEL> follows a self-inserting character command, you can think of it as canceling that command. However, avoid the mistake of thinking of <DEL> as a general way to cancel a command!

When your mistake is longer than a couple of characters, it might be more convenient to use M-<DEL> or C-x <DEL>. M-<DEL> kills back to the start of the last word, and C-x <DEL> kills back to the start of the last sentence. C-x <DEL> is particularly useful when you change your mind about the phrasing of the text you are writing. M-<DEL> and C-x <DEL> save the killed text for C-y and M-y to retrieve. See Yanking.

M-<DEL> is often useful even when you have typed only a few characters wrong, if you know you are confused in your typing and aren't sure exactly what you typed. At such a time, you cannot correct with <DEL> except by looking at the screen to see what you did. Often it requires less thought to kill the whole word and start again.

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21.2 Transposing Text

Transpose two characters (transpose-chars).
Transpose two words (transpose-words).
Transpose two balanced expressions (transpose-sexps).
C-x C-t
Transpose two lines (transpose-lines).

The common error of transposing two characters can be fixed, when they are adjacent, with the C-t command (transpose-chars). Normally, C-t transposes the two characters on either side of point. When given at the end of a line, rather than transposing the last character of the line with the newline, which would be useless, C-t transposes the last two characters on the line. So, if you catch your transposition error right away, you can fix it with just a C-t. If you don't catch it so fast, you must move the cursor back between the two transposed characters before you type C-t. If you transposed a space with the last character of the word before it, the word motion commands are a good way of getting there. Otherwise, a reverse search (C-r) is often the best way. See Search.

M-t transposes the word before point with the word after point (transpose-words). It moves point forward over a word, dragging the word preceding or containing point forward as well. The punctuation characters between the words do not move. For example, ‘FOO, BAR transposes into ‘BAR, FOO rather than ‘BAR FOO,’.

C-M-t (transpose-sexps) is a similar command for transposing two expressions (see Expressions), and C-x C-t (transpose-lines) exchanges lines. They work like M-t except as regards what units of text they transpose.

A numeric argument to a transpose command serves as a repeat count: it tells the transpose command to move the character (word, expression, line) before or containing point across several other characters (words, expressions, lines). For example, C-u 3 C-t moves the character before point forward across three other characters. It would change ‘f-!-oobar’ into ‘oobf-!-ar’. This is equivalent to repeating C-t three times. C-u - 4 M-t moves the word before point backward across four words. C-u - C-M-t would cancel the effect of plain C-M-t.

A numeric argument of zero is assigned a special meaning (because otherwise a command with a repeat count of zero would do nothing): to transpose the character (word, expression, line) ending after point with the one ending after the mark.

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21.3 Case Conversion

M-- M-l
Convert last word to lower case. Note Meta-- is Meta-minus.
M-- M-u
Convert last word to all upper case.
M-- M-c
Convert last word to lower case with capital initial.

A very common error is to type words in the wrong case. Because of this, the word case-conversion commands M-l, M-u and M-c have a special feature when used with a negative argument: they do not move the cursor. As soon as you see you have mistyped the last word, you can simply case-convert it and go on typing. See Case.

Previous: Fixing Case, Up: Fixit

21.4 Checking and Correcting Spelling

This section describes the commands to check the spelling of a single word or of a portion of a buffer. These commands work with the spelling checker program Ispell, which is not part of Emacs.

M-x flyspell-mode
Enable Flyspell mode, which highlights all misspelled words.
M-x flyspell-prog-mode
Enable Flyspell mode for comments and strings only.
Check and correct spelling of the word at point (ispell-word).
Complete the word before point based on the spelling dictionary (ispell-complete-word).
M-x ispell
Spell-check the active region or the current buffer.
M-x ispell-buffer
Check and correct spelling of each word in the buffer.
M-x ispell-region
Check and correct spelling of each word in the region.
M-x ispell-message
Check and correct spelling of each word in a draft mail message, excluding cited material.
M-x ispell-change-dictionary <RET> dict <RET>
Restart the Ispell process, using dict as the dictionary.
M-x ispell-kill-ispell
Kill the Ispell subprocess.

Flyspell mode is a fully-automatic way to check spelling as you edit in Emacs. It operates by checking words as you change or insert them. When it finds a word that it does not recognize, it highlights that word. This does not interfere with your editing, but when you see the highlighted word, you can move to it and fix it. Type M-x flyspell-mode to enable or disable this mode in the current buffer.

When Flyspell mode highlights a word as misspelled, you can click on it with Mouse-2 to display a menu of possible corrections and actions. You can also correct the word by editing it manually in any way you like.

Flyspell Prog mode works just like ordinary Flyspell mode, except that it only checks words in comments and string constants. This feature is useful for editing programs. Type M-x flyspell-prog-mode to enable or disable this mode in the current buffer.

The other Emacs spell-checking features check or look up words when you give an explicit command to do so.

To check the spelling of the word around or before point, and optionally correct it as well, use the command M-$ (ispell-word). If the word is not correct, the command offers you various alternatives for what to do about it.

To check the entire current buffer, use M-x ispell-buffer. Use M-x ispell-region to check just the current region. To check spelling in an email message you are writing, use M-x ispell-message; that command checks the whole buffer, except for material that is indented or appears to be cited from other messages.

The M-x ispell command spell-checks the active region if the Transient Mark mode is on (see Transient Mark), otherwise it spell-checks the current buffer.

Each time these commands encounter an incorrect word, they ask you what to do. They display a list of alternatives, usually including several “near-misses”—words that are close to the word being checked. Then you must type a single-character response. Here are the valid responses:

Skip this word—continue to consider it incorrect, but don't change it here.
r new <RET>
Replace the word (just this time) with new. (The replacement string will be rescanned for more spelling errors.)
R new <RET>
Replace the word with new, and do a query-replace so you can replace it elsewhere in the buffer if you wish. (The replacements will be rescanned for more spelling errors.)
Replace the word (just this time) with one of the displayed near-misses. Each near-miss is listed with a digit; type that digit to select it.
Accept the incorrect word—treat it as correct, but only in this editing session.
Accept the incorrect word—treat it as correct, but only in this editing session and for this buffer.
Insert this word in your private dictionary file so that Ispell will consider it correct from now on, even in future sessions.
Insert the lower-case version of this word in your private dictionary file.
Like i, but you can also specify dictionary completion information.
l word <RET>
Look in the dictionary for words that match word. These words become the new list of “near-misses”; you can select one of them as the replacement by typing a digit. You can use ‘*’ in word as a wildcard.
Quit interactive spell checking, leaving point at the word that was being checked. You can restart checking again afterward with C-u M-$.
Same as C-g.
Quit interactive spell checking and move point back to where it was when you started spell checking.
Quit interactive spell checking and kill the Ispell subprocess.
Refresh the screen.
This key has its normal command meaning (suspend Emacs or iconify this frame).
Show the list of options.

The command ispell-complete-word, which is bound to the key M-<TAB> in Text mode and related modes, shows a list of completions based on spelling correction. Insert the beginning of a word, and then type M-<TAB>; the command displays a completion list window. (If your window manager intercepts M-<TAB>, type <ESC> <TAB> or C-M-i.) To choose one of the completions listed, click Mouse-2 or Mouse-1 fast on it, or move the cursor there in the completions window and type <RET>. See Text Mode.

Once started, the Ispell subprocess continues to run (waiting for something to do), so that subsequent spell checking commands complete more quickly. If you want to get rid of the Ispell process, use M-x ispell-kill-ispell. This is not usually necessary, since the process uses no time except when you do spelling correction.

Ispell uses two dictionaries together for spell checking: the standard dictionary and your private dictionary. The variable ispell-dictionary specifies the file name to use for the standard dictionary; a value of nil selects the default dictionary. The command M-x ispell-change-dictionary sets this variable and then restarts the Ispell subprocess, so that it will use a different standard dictionary.

Ispell uses a separate dictionary for word completion. The variable ispell-complete-word-dict specifies the file name of this dictionary. The completion dictionary must be different because it cannot use root and affix information. For some languages there is a spell checking dictionary but no word completion dictionary.

Next: , Previous: Fixit, Up: Top

22 Keyboard Macros

In this chapter we describe how a sequence of editing commands can be recorded and repeated multiple times.

A keyboard macro is a command defined by the user to stand for another sequence of keys. For example, if you discover that you are about to type C-n C-d forty times, you can speed your work by defining a keyboard macro to do C-n C-d and calling it with a repeat count of forty.

You define a keyboard macro while executing the commands which are the definition. Put differently, as you define a keyboard macro, the definition is being executed for the first time. This way, you can see what the effects of your commands are, so that you don't have to figure them out in your head. When you are finished, the keyboard macro is defined and also has been, in effect, executed once. You can then do the whole thing over again by invoking the macro.

Keyboard macros differ from ordinary Emacs commands in that they are written in the Emacs command language rather than in Lisp. This makes it easier for the novice to write them, and makes them more convenient as temporary hacks. However, the Emacs command language is not powerful enough as a programming language to be useful for writing anything intelligent or general. For such things, Lisp must be used.

Next: , Up: Keyboard Macros

22.1 Basic Use

C-x (
Start defining a keyboard macro (kmacro-start-macro).
C-x )
End the definition of a keyboard macro (kmacro-end-macro).
C-x e
Execute the most recent keyboard macro (kmacro-end-and-call-macro). First end the definition of the keyboard macro, if currently defining it. To immediately execute the keyboard macro again, just repeat the e.
If a keyboard macro is being defined, end the definition; otherwise, execute the most recent keyboard macro (kmacro-end-or-call-macro).
C-u C-x (
Re-execute last keyboard macro, then add more keys to its definition.
C-u C-u C-x (
Add more keys to the last keyboard macro without re-executing it.
C-x q
When this point is reached during macro execution, ask for confirmation (kbd-macro-query).
C-x C-k n
Give a command name (for the duration of the session) to the most recently defined keyboard macro (kmacro-name-last-macro).
C-x C-k b
Bind the most recently defined keyboard macro to a key sequence (for the duration of the session) (kmacro-bind-to-key).
M-x insert-kbd-macro
Insert in the buffer a keyboard macro's definition, as Lisp code.
C-x C-k e
Edit a previously defined keyboard macro (edit-kbd-macro).
C-x C-k r
Run the last keyboard macro on each line that begins in the region (apply-macro-to-region-lines).

To start defining a keyboard macro, type the C-x ( command (kmacro-start-macro). From then on, your keys continue to be executed, but also become part of the definition of the macro. ‘Def’ appears in the mode line to remind you of what is going on. When you are finished, the C-x ) command (kmacro-end-macro) terminates the definition (without becoming part of it!). For example,

     C-x ( M-f foo C-x )

defines a macro to move forward a word and then insert ‘foo’.

The macro thus defined can be invoked again with the C-x e command (kmacro-end-and-call-macro), which may be given a repeat count as a numeric argument to execute the macro many times. If you enter C-x e while defining a macro, the macro is terminated and executed immediately.

After executing the macro with C-x e, you can use e repeatedly to immediately repeat the macro one or more times. For example,

     C-x ( xyz C-x e e e

inserts ‘xyzxyzxyzxyz’ in the current buffer.

C-x ) can also be given a repeat count as an argument, in which case it repeats the macro that many times right after defining it, but defining the macro counts as the first repetition (since it is executed as you define it). Therefore, giving C-x ) an argument of 4 executes the macro immediately 3 additional times. An argument of zero to C-x e or C-x ) means repeat the macro indefinitely (until it gets an error or you type C-g or, on MS-DOS, C-<BREAK>).

The key <F4> is like a combination of C-x ) and C-x e. If you're defining a macro, <F4> ends the definition. Otherwise it executes the last macro.

If you wish to repeat an operation at regularly spaced places in the text, define a macro and include as part of the macro the commands to move to the next place you want to use it. For example, if you want to change each line, you should position point at the start of a line, and define a macro to change that line and leave point at the start of the next line. Then repeating the macro will operate on successive lines.

When a command reads an argument with the minibuffer, your minibuffer input becomes part of the macro along with the command. So when you replay the macro, the command gets the same argument as when you entered the macro. For example,

     C-x ( C-a C-<SPC> C-n M-w C-x b f o o <RET> C-y C-x b <RET> C-x )

defines a macro that copies the current line into the buffer ‘foo’, then returns to the original buffer.

You can use function keys in a keyboard macro, just like keyboard keys. You can even use mouse events, but be careful about that: when the macro replays the mouse event, it uses the original mouse position of that event, the position that the mouse had while you were defining the macro. The effect of this may be hard to predict. (Using the current mouse position would be even less predictable.)

One thing that doesn't always work well in a keyboard macro is the command C-M-c (exit-recursive-edit). When this command exits a recursive edit that started within the macro, it works as you'd expect. But if it exits a recursive edit that started before you invoked the keyboard macro, it also necessarily exits the keyboard macro as part of the process.

After you have terminated the definition of a keyboard macro, you can add to the end of its definition by typing C-u C-x (. This is equivalent to plain C-x ( followed by retyping the whole definition so far. As a consequence it re-executes the macro as previously defined.

You can also add to the end of the definition of the last keyboard macro without re-executing it by typing C-u C-u C-x (.

The variable kmacro-execute-before-append specifies whether a single C-u prefix causes the existing macro to be re-executed before appending to it.

The command C-x C-k r (apply-macro-to-region-lines) repeats the last defined keyboard macro on each line that begins in the region. It does this line by line, by moving point to the beginning of the line and then executing the macro.

Next: , Previous: Basic Keyboard Macro, Up: Keyboard Macros

22.2 The Keyboard Macro Ring

All defined keyboard macros are recorded in the “keyboard macro ring”, a list of sequences of keys. There is only one keyboard macro ring, shared by all buffers.

All commands which operate on the keyboard macro ring use the same C-x C-k prefix. Most of these commands can be executed and repeated immediately after each other without repeating the C-x C-k prefix. For example,

     C-x C-k C-p C-p C-k C-k C-k C-n C-n C-k C-p C-k C-d

will rotate the keyboard macro ring to the “second previous” macro, execute the resulting head macro three times, rotate back to the original head macro, execute that once, rotate to the “previous” macro, execute that, and finally delete it from the macro ring.

The command C-x C-k C-k (kmacro-end-or-call-macro-repeat) executes the keyboard macro at the head of the macro ring. You can repeat the macro immediately by typing another C-k, or you can rotate the macro ring immediately by typing C-n or C-p.

When a keyboard macro is being defined, C-x C-k C-k behaves like C-x ) except that, immediately afterward, you can use most key bindings of this section without the C-x C-k prefix. For instance, another C-k will re-execute the macro.

The commands C-x C-k C-n (kmacro-cycle-ring-next) and C-x C-k C-p (kmacro-cycle-ring-previous) rotate the macro ring, bringing the next or previous keyboard macro to the head of the macro ring. The definition of the new head macro is displayed in the echo area. You can continue to rotate the macro ring immediately by repeating just C-n and C-p until the desired macro is at the head of the ring. To execute the new macro ring head immediately, just type C-k.

Note that Emacs treats the head of the macro ring as the “last defined keyboard macro”. For instance, it is the keyboard macro that C-x e will execute.

The command C-x C-k C-v (kmacro-view-macro-repeat) displays the last keyboard macro, or when repeated (with C-v), it displays the previous macro on the macro ring, just like C-x C-k C-p, but without actually rotating the macro ring. If you enter C-k immediately after displaying a macro from the ring, that macro is executed, but still without altering the macro ring.

So while e.g. C-x C-k C-p C-p C-p C-k C-k makes the 3rd previous macro the current macro and executes it twice, C-x C-k C-v C-v C-v C-k C-k will display and execute the 3rd previous macro once and then the current macro once.

The command C-x C-k C-d (kmacro-delete-ring-head) removes and deletes the macro currently at the head of the macro ring. You can use this to delete a macro that didn't work as expected, or which you don't need anymore.

The command C-x C-k C-t (kmacro-swap-ring) interchanges the head of the macro ring with the previous element on the macro ring.

The command C-x C-k C-l (kmacro-call-ring-2nd-repeat) executes the previous (rather than the head) element on the macro ring.

The maximum number of macros stored in the keyboard macro ring is determined by the customizable variable kmacro-ring-max.

Next: , Previous: Keyboard Macro Ring, Up: Keyboard Macros

22.3 The Keyboard Macro Counter

Each keyboard macro has an associated counter. Normally, the macro counter is initialized to 0 when you start defining the macro, and incremented by 1 after each insertion of the counter value; that is, if you insert the macro counter twice while defining the macro, the counter will increase by 2 on each repetition of the macro.

The command C-x C-k C-i (kmacro-insert-counter) inserts the current value of the keyboard macro counter and increments the counter by 1. You can use a numeric prefix argument to specify a different increment. If you just specify a C-u prefix, the last inserted counter value is repeated and the counter is not incremented. For example, if you enter the following sequence while defining a macro

     C-x C-k C-i C-x C-k C-i C-u C-x C-k C-i C-x C-k C-i

the text ‘0112’ is inserted in the buffer, and for the first and second execution of the macro ‘3445’ and ‘6778’ are inserted.

This command usually only makes sense while defining a keyboard macro. But its behavior when no keyboard macro is being defined or executed is predictable: it inserts and increments the counter of the head of the keyboard macro ring.

The command C-x C-k C-c (kmacro-set-counter) prompts for the initial value of the keyboard macro counter if you use it before you define a keyboard macro. If you use it before executing a keyboard macro, it resets that macro's counter. If you use it while defining a keyboard macro, then the macro counter gets reset to that same value on each repetition of the macro. Rather than having the command prompt for a value, you can also specify the value with a numeric prefix argument. If you just specify a C-u prefix, the counter is reset to the value it had prior to the current repetition of the macro (undoing any increments so far in this repetition). If you just specify a C-u prefix while no macro is being defined or executed, then the new value of the counter is essentially unpredictable.

The command C-x C-k C-a (kmacro-add-counter) prompts for a value to add to the macro counter. You can also specify the value with a numeric prefix argument. If you just specify a C-u prefix, the counter is reset to the last value inserted by any keyboard macro. Usually, this will only make sense if that value was inserted during the current macro definition or repetition.

This command normally only makes sense while defining a keyboard macro. But its behavior when no keyboard macro is being defined or executed is predictable: it affects the counter of the head of the keyboard macro ring.

The command C-x C-k C-f (kmacro-set-format) prompts for the format to use when inserting the macro counter. The default format is ‘%d’, which means to insert the number in decimal without any padding. You can exit with empty minibuffer to reset the format to this default. You can specify any format string that the format function accepts and that makes sense with a single integer extra argument (see Formatting Strings). Do not put the format string inside double quotes when you insert it in the minibuffer.

If you use this command while no keyboard macro is being defined or executed, the new format affects all subsequent macro definitions. Existing macros continue to use the format in effect when they were defined. If you set the format while defining a keyboard macro, this affects the macro being defined from that point on, but it does not affect subsequent macros. Execution of the macro will, at each step, use the format in effect at that step during its definition. Changes to the macro format during execution of a macro, like the corresponding changes during its definition, have no effect on subsequent macros.

The format set by C-x C-k C-f does not affect insertion of numbers stored in registers.

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22.4 Executing Macros with Variations

Using C-x q (kbd-macro-query), you can get an effect similar to that of query-replace, where the macro asks you each time around whether to make a change. While defining the macro, type C-x q at the point where you want the query to occur. During macro definition, the C-x q does nothing, but when you run the macro later, C-x q asks you interactively whether to continue.

The valid responses when C-x q asks are <SPC> (or y), <DEL> (or n), <RET> (or q), C-l and C-r. The answers are the same as in query-replace, though not all of the query-replace options are meaningful.

These responses include <SPC> to continue, and <DEL> to skip the remainder of this repetition of the macro and start right away with the next repetition. <RET> means to skip the remainder of this repetition and cancel further repetitions. C-l redraws the screen and asks you again for a character to say what to do.

C-r enters a recursive editing level, in which you can perform editing which is not part of the macro. When you exit the recursive edit using C-M-c, you are asked again how to continue with the keyboard macro. If you type a <SPC> at this time, the rest of the macro definition is executed. It is up to you to leave point and the text in a state such that the rest of the macro will do what you want.

C-u C-x q, which is C-x q with a numeric argument, performs a completely different function. It enters a recursive edit reading input from the keyboard, both when you type it during the definition of the macro, and when it is executed from the macro. During definition, the editing you do inside the recursive edit does not become part of the macro. During macro execution, the recursive edit gives you a chance to do some particularized editing on each repetition. See Recursive Edit.

Another way to vary the behavior of a keyboard macro is to use a register as a counter, incrementing it on each repetition of the macro. See RegNumbers.

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22.5 Naming and Saving Keyboard Macros

If you wish to save a keyboard macro for later use, you can give it a name using C-x C-k n (kmacro-name-last-macro). This reads a name as an argument using the minibuffer and defines that name to execute the last keyboard macro, in its current form. (If you later add to the definition of this macro, that does not alter the name's definition as a macro.) The macro name is a Lisp symbol, and defining it in this way makes it a valid command name for calling with M-x or for binding a key to with global-set-key (see Keymaps). If you specify a name that has a prior definition other than a keyboard macro, an error message is shown and nothing is changed.

You can also bind the last keyboard macro (in its current form) to a key, using C-x C-k b (kmacro-bind-to-key) followed by the key sequence you want to bind. You can bind to any key sequence in the global keymap, but since most key sequences already have other bindings, you should select the key sequence carefully. If you try to bind to a key sequence with an existing binding (in any keymap), this command asks you for confirmation before replacing the existing binding.

To avoid problems caused by overriding existing bindings, the key sequences C-x C-k 0 through C-x C-k 9 and C-x C-k A through C-x C-k Z are reserved for your own keyboard macro bindings. In fact, to bind to one of these key sequences, you only need to type the digit or letter rather than the whole key sequences. For example,

     C-x C-k b 4

will bind the last keyboard macro to the key sequence C-x C-k 4.

Once a macro has a command name, you can save its definition in a file. Then it can be used in another editing session. First, visit the file you want to save the definition in. Then use this command:

     M-x insert-kbd-macro <RET> macroname <RET>

This inserts some Lisp code that, when executed later, will define the same macro with the same definition it has now. (You need not understand Lisp code to do this, because insert-kbd-macro writes the Lisp code for you.) Then save the file. You can load the file later with load-file (see Lisp Libraries). If the file you save in is your init file ~/.emacs (see Init File) then the macro will be defined each time you run Emacs.

If you give insert-kbd-macro a numeric argument, it makes additional Lisp code to record the keys (if any) that you have bound to macroname, so that the macro will be reassigned the same keys when you load the file.

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22.6 Editing a Keyboard Macro

You can edit the last keyboard macro by typing C-x C-k C-e or C-x C-k RET (kmacro-edit-macro). This formats the macro definition in a buffer and enters a specialized major mode for editing it. Type C-h m once in that buffer to display details of how to edit the macro. When you are finished editing, type C-c C-c.

You can edit a named keyboard macro or a macro bound to a key by typing C-x C-k e (edit-kbd-macro). Follow that with the keyboard input that you would use to invoke the macro—C-x e or M-x name or some other key sequence.

You can edit the last 100 keystrokes as a macro by typing C-x C-k l (kmacro-edit-lossage).

Previous: Edit Keyboard Macro, Up: Keyboard Macros

22.7 Stepwise Editing a Keyboard Macro

You can interactively replay and edit the last keyboard macro, one command at a time, by typing C-x C-k SPC (kmacro-step-edit-macro). Unless you quit the macro using q or C-g, the edited macro replaces the last macro on the macro ring.

This macro editing feature shows the last macro in the minibuffer together with the first (or next) command to be executed, and prompts you for an action. You can enter ? to get a summary of your options. These actions are available:

Next: , Previous: Keyboard Macros, Up: Top

23 File Handling

The operating system stores data permanently in named files, so most of the text you edit with Emacs comes from a file and is ultimately stored in a file.

To edit a file, you must tell Emacs to read the file and prepare a buffer containing a copy of the file's text. This is called visiting the file. Editing commands apply directly to text in the buffer; that is, to the copy inside Emacs. Your changes appear in the file itself only when you save the buffer back into the file.

In addition to visiting and saving files, Emacs can delete, copy, rename, and append to files, keep multiple versions of them, and operate on file directories.

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23.1 File Names

Most Emacs commands that operate on a file require you to specify the file name. (Saving and reverting are exceptions; the buffer knows which file name to use for them.) You enter the file name using the minibuffer (see Minibuffer). Completion is available (see Completion) to make it easier to specify long file names. When completing file names, Emacs ignores those whose file-name extensions appear in the variable completion-ignored-extensions; see Completion Options.

For most operations, there is a default file name which is used if you type just <RET> to enter an empty argument. Normally the default file name is the name of the file visited in the current buffer; this makes it easy to operate on that file with any of the Emacs file commands.

Each buffer has a default directory which is normally the same as the directory of the file visited in that buffer. When you enter a file name without a directory, the default directory is used. If you specify a directory in a relative fashion, with a name that does not start with a slash, it is interpreted with respect to the default directory. The default directory is kept in the variable default-directory, which has a separate value in every buffer.

For example, if the default file name is /u/rms/gnu/gnu.tasks then the default directory is /u/rms/gnu/. If you type just ‘foo’, which does not specify a directory, it is short for /u/rms/gnu/foo. ‘../.login’ would stand for /u/rms/.login. ‘new/foo’ would stand for the file name /u/rms/gnu/new/foo.

The command M-x pwd displays the current buffer's default directory, and the command M-x cd sets it (to a value read using the minibuffer). A buffer's default directory changes only when the cd command is used. A file-visiting buffer's default directory is initialized to the directory of the file that is visited in that buffer. If you create a buffer with C-x b, its default directory is copied from that of the buffer that was current at the time.

The default directory actually appears in the minibuffer when the minibuffer becomes active to read a file name. This serves two purposes: it shows you what the default is, so that you can type a relative file name and know with certainty what it will mean, and it allows you to edit the default to specify a different directory. This insertion of the default directory is inhibited if the variable insert-default-directory is set to nil.

Note that it is legitimate to type an absolute file name after you enter the minibuffer, ignoring the presence of the default directory name as part of the text. The final minibuffer contents may look invalid, but that is not so. For example, if the minibuffer starts out with ‘/usr/tmp/’ and you add ‘/x1/rms/foo’, you get ‘/usr/tmp//x1/rms/foo’; but Emacs ignores everything through the first slash in the double slash; the result is ‘/x1/rms/foo’. See Minibuffer File.

$’ in a file name is used to substitute an environment variable. The environment variable name consists of all the alphanumeric characters after the ‘$’; alternatively, it can be enclosed in braces after the ‘$’. For example, if you have used the shell command export FOO=rms/hacks to set up an environment variable named FOO, then you can use /u/$FOO/test.c or /u/${FOO}/test.c as an abbreviation for /u/rms/hacks/test.c. If the environment variable is not defined, no substitution occurs: /u/$notdefined stands for itself (assuming the environment variable notdefined is not defined).

Note that shell commands to set environment variables affect Emacs only when done before Emacs is started.

You can use ~/ in a file name to mean your home directory, or ~user-id/ to mean the home directory of a user whose login name is user-id. (On DOS and Windows systems, where a user doesn't have a home directory, Emacs substitutes ~/ with the value of the environment variable HOME; see General Variables.)

To access a file with ‘$’ in its name, if the ‘$’ causes expansion, type ‘$$’. This pair is converted to a single ‘$’ at the same time as variable substitution is performed for a single ‘$’. Alternatively, quote the whole file name with ‘/:’ (see Quoted File Names). File names which begin with a literal ‘~’ should also be quoted with ‘/:’.

The Lisp function that performs the substitution is called substitute-in-file-name. The substitution is performed only on file names read as such using the minibuffer.

You can include non-ASCII characters in file names if you set the variable file-name-coding-system to a non-nil value. See Specify Coding.

Next: , Previous: File Names, Up: Files

23.2 Visiting Files

C-x C-f
Visit a file (find-file).
C-x C-r
Visit a file for viewing, without allowing changes to it (find-file-read-only).
C-x C-v
Visit a different file instead of the one visited last (find-alternate-file).
C-x 4 f
Visit a file, in another window (find-file-other-window). Don't alter what is displayed in the selected window.
C-x 5 f
Visit a file, in a new frame (find-file-other-frame). Don't alter what is displayed in the selected frame.
M-x find-file-literally
Visit a file with no conversion of the contents.

Visiting a file means copying its contents into an Emacs buffer so you can edit them. Emacs makes a new buffer for each file that you visit. We often say that this buffer “is visiting” that file, or that the buffer's “visited file” is that file. Emacs constructs the buffer name from the file name by throwing away the directory, keeping just the name proper. For example, a file named /usr/rms/emacs.tex would get a buffer named ‘emacs.tex’. If there is already a buffer with that name, Emacs constructs a unique name—the normal method is to append ‘<2>’, ‘<3>’, and so on, but you can select other methods (see Uniquify).

Each window's mode line shows the name of the buffer that is being displayed in that window, so you can always tell what buffer you are editing.

The changes you make with editing commands are made in the Emacs buffer. They do not take effect in the file that you visited, or any place permanent, until you save the buffer. Saving the buffer means that Emacs writes the current contents of the buffer into its visited file. See Saving.

If a buffer contains changes that have not been saved, we say the buffer is modified. This is important because it implies that some changes will be lost if the buffer is not saved. The mode line displays two stars near the left margin to indicate that the buffer is modified.

To visit a file, use the command C-x C-f (find-file). Follow the command with the name of the file you wish to visit, terminated by a <RET>.

The file name is read using the minibuffer (see Minibuffer), with defaulting and completion in the standard manner (see File Names). While in the minibuffer, you can abort C-x C-f by typing C-g. File-name completion ignores certain filenames; for more about this, see Completion Options.

Your confirmation that C-x C-f has completed successfully is the appearance of new text on the screen and a new buffer name in the mode line. If the specified file does not exist and could not be created, or cannot be read, then you get an error, with an error message displayed in the echo area.

If you visit a file that is already in Emacs, C-x C-f does not make another copy. It selects the existing buffer containing that file. However, before doing so, it checks that the file itself has not changed since you visited or saved it last. If the file has changed, a warning message is shown. See Simultaneous Editing.

If you try to visit a file larger than large-file-warning-threshold (the default is 10000000, which is about 10 megabytes), Emacs will ask you for confirmation first. You can answer y to proceed with visiting the file. Note, however, that Emacs cannot visit files that are larger than the maximum Emacs buffer size, which is around 256 megabytes on 32-bit machines (see Buffers). If you try, Emacs will display an error message saying that the maximum buffer size has been exceeded.

On graphical terminals, there are two additional methods for visiting files. Firstly, when Emacs is built with a suitable GUI toolkit, commands invoked with the mouse (by clicking on the menu bar or tool bar) use the toolkit's standard File Selection dialog instead of prompting for the file name in the minibuffer. On Unix and GNU/Linux platforms, Emacs does that when built with GTK, LessTif, and Motif toolkits; on MS-Windows, the GUI version does that by default. For information on how to customize this, see Dialog Boxes.

Secondly, Emacs supports the “drag and drop” protocol on the X window system. Dropping a file into an ordinary Emacs window visits the file using that window. However, dropping a file into a window displaying a Dired buffer moves or copies the file into the displayed directory. For details, see Drag and Drop, Misc Dired Features.

What if you want to create a new file? Just visit it. Emacs displays ‘(New file)’ in the echo area, but in other respects behaves as if you had visited an existing empty file. If you make any changes and save them, the file is created.

Emacs recognizes from the contents of a file which convention it uses to separate lines—newline (used on GNU/Linux and on Unix), carriage-return linefeed (used on Microsoft systems), or just carriage-return (used on the Macintosh)—and automatically converts the contents to the normal Emacs convention, which is that the newline character separates lines. This is a part of the general feature of coding system conversion (see Coding Systems), and makes it possible to edit files imported from different operating systems with equal convenience. If you change the text and save the file, Emacs performs the inverse conversion, changing newlines back into carriage-return linefeed or just carriage-return if appropriate.

If the file you specify is actually a directory, C-x C-f invokes Dired, the Emacs directory browser, so that you can “edit” the contents of the directory (see Dired). Dired is a convenient way to view, delete, or operate on the files in the directory. However, if the variable find-file-run-dired is nil, then it is an error to try to visit a directory.

Files which are actually collections of other files, or file archives, are visited in special modes which invoke a Dired-like environment to allow operations on archive members. See File Archives, for more about these features.

If the file name you specify contains shell-style wildcard characters, Emacs visits all the files that match it. Wildcards include ‘?’, ‘*’, and ‘[...]’ sequences. To enter the wild card ‘?’ in a file name in the minibuffer, you need to type C-q ?. See Quoted File Names, for information on how to visit a file whose name actually contains wildcard characters. You can disable the wildcard feature by customizing find-file-wildcards.

If you visit a file that the operating system won't let you modify, or that is marked read-only, Emacs makes the buffer read-only too, so that you won't go ahead and make changes that you'll have trouble saving afterward. You can make the buffer writable with C-x C-q (toggle-read-only). See Misc Buffer.

If you want to visit a file as read-only in order to protect yourself from entering changes accidentally, visit it with the command C-x C-r (find-file-read-only) instead of C-x C-f.

If you visit a nonexistent file unintentionally (because you typed the wrong file name), use the C-x C-v command (find-alternate-file) to visit the file you really wanted. C-x C-v is similar to C-x C-f, but it kills the current buffer (after first offering to save it if it is modified). When C-x C-v reads the file name to visit, it inserts the entire default file name in the buffer, with point just after the directory part; this is convenient if you made a slight error in typing the name.

If you find a file which exists but cannot be read, C-x C-f signals an error.

C-x 4 f (find-file-other-window) is like C-x C-f except that the buffer containing the specified file is selected in another window. The window that was selected before C-x 4 f continues to show the same buffer it was already showing. If this command is used when only one window is being displayed, that window is split in two, with one window showing the same buffer as before, and the other one showing the newly requested file. See Windows.

C-x 5 f (find-file-other-frame) is similar, but opens a new frame, or makes visible any existing frame showing the file you seek. This feature is available only when you are using a window system. See Frames.

If you wish to edit a file as a sequence of ASCII characters with no special encoding or conversion, use the M-x find-file-literally command. It visits a file, like C-x C-f, but does not do format conversion (see Formatted Text), character code conversion (see Coding Systems), or automatic uncompression (see Compressed Files), and does not add a final newline because of require-final-newline. If you already have visited the same file in the usual (non-literal) manner, this command asks you whether to visit it literally instead.

Two special hook variables allow extensions to modify the operation of visiting files. Visiting a file that does not exist runs the functions in the list find-file-not-found-functions; this variable holds a list of functions, and the functions are called one by one (with no arguments) until one of them returns non-nil. This is not a normal hook, and the name ends in ‘-functions’ rather than ‘-hook’ to indicate that fact.

Successful visiting of any file, whether existing or not, calls the functions in the list find-file-hook, with no arguments. This variable is a normal hook. In the case of a nonexistent file, the find-file-not-found-functions are run first. See Hooks.

There are several ways to specify automatically the major mode for editing the file (see Choosing Modes), and to specify local variables defined for that file (see File Variables).

Next: , Previous: Visiting, Up: Files

23.3 Saving Files

Saving a buffer in Emacs means writing its contents back into the file that was visited in the buffer.

Next: , Up: Saving

23.3.1 Commands for Saving Files

These are the commands that relate to saving and writing files.

C-x C-s
Save the current buffer in its visited file on disk (save-buffer).
C-x s
Save any or all buffers in their visited files (save-some-buffers).
Forget that the current buffer has been changed (not-modified). With prefix argument (C-u), mark the current buffer as changed.
C-x C-w
Save the current buffer as a specified file name (write-file).
M-x set-visited-file-name
Change the file name under which the current buffer will be saved.

When you wish to save the file and make your changes permanent, type C-x C-s (save-buffer). After saving is finished, C-x C-s displays a message like this:

     Wrote /u/rms/gnu/gnu.tasks

If the selected buffer is not modified (no changes have been made in it since the buffer was created or last saved), saving is not really done, because it would have no effect. Instead, C-x C-s displays a message like this in the echo area:

     (No changes need to be saved)

The command C-x s (save-some-buffers) offers to save any or all modified buffers. It asks you what to do with each buffer. The possible responses are analogous to those of query-replace:

Save this buffer and ask about the rest of the buffers.
Don't save this buffer, but ask about the rest of the buffers.
Save this buffer and all the rest with no more questions.
Terminate save-some-buffers without any more saving.
Save this buffer, then exit save-some-buffers without even asking about other buffers.
View the buffer that you are currently being asked about. When you exit View mode, you get back to save-some-buffers, which asks the question again.
Diff the buffer against its corresponding file, so you can see what changes you would be saving.
Display a help message about these options.

C-x C-c, the key sequence to exit Emacs, invokes save-some-buffers and therefore asks the same questions.

If you have changed a buffer but you do not want to save the changes, you should take some action to prevent it. Otherwise, each time you use C-x s or C-x C-c, you are liable to save this buffer by mistake. One thing you can do is type M-~ (not-modified), which clears out the indication that the buffer is modified. If you do this, none of the save commands will believe that the buffer needs to be saved. (‘~’ is often used as a mathematical symbol for `not'; thus M-~ is `not', metafied.) You could also use set-visited-file-name (see below) to mark the buffer as visiting a different file name, one which is not in use for anything important. Alternatively, you can cancel all the changes made since the file was visited or saved, by reading the text from the file again. This is called reverting. See Reverting. You could also undo all the changes by repeating the undo command C-x u until you have undone all the changes; but reverting is easier.

M-x set-visited-file-name alters the name of the file that the current buffer is visiting. It reads the new file name using the minibuffer. Then it marks the buffer as visiting that file name, and changes the buffer name correspondingly. set-visited-file-name does not save the buffer in the newly visited file; it just alters the records inside Emacs in case you do save later. It also marks the buffer as “modified” so that C-x C-s in that buffer will save.

If you wish to mark the buffer as visiting a different file and save it right away, use C-x C-w (write-file). It is equivalent to set-visited-file-name followed by C-x C-s (except that C-x C-w asks for confirmation if the file exists). C-x C-s used on a buffer that is not visiting a file has the same effect as C-x C-w; that is, it reads a file name, marks the buffer as visiting that file, and saves it there. The default file name in a buffer that is not visiting a file is made by combining the buffer name with the buffer's default directory (see File Names).

If the new file name implies a major mode, then C-x C-w switches to that major mode, in most cases. The command set-visited-file-name also does this. See Choosing Modes.

If Emacs is about to save a file and sees that the date of the latest version on disk does not match what Emacs last read or wrote, Emacs notifies you of this fact, because it probably indicates a problem caused by simultaneous editing and requires your immediate attention. See Simultaneous Editing.

Next: , Previous: Save Commands, Up: Saving

23.3.2 Backup Files

On most operating systems, rewriting a file automatically destroys all record of what the file used to contain. Thus, saving a file from Emacs throws away the old contents of the file—or it would, except that Emacs carefully copies the old contents to another file, called the backup file, before actually saving.

For most files, the variable make-backup-files determines whether to make backup files. On most operating systems, its default value is t, so that Emacs does write backup files.

For files managed by a version control system (see Version Control), the variable vc-make-backup-files determines whether to make backup files. By default it is nil, since backup files are redundant when you store all the previous versions in a version control system. See General VC Options.

The default value of the backup-enable-predicate variable prevents backup files being written for files in the directories used for temporary files, specified by temporary-file-directory or small-temporary-file-directory.

At your option, Emacs can keep either a single backup file or a series of numbered backup files for each file that you edit.

Emacs makes a backup for a file only the first time the file is saved from one buffer. No matter how many times you save a file, its backup file continues to contain the contents from before the file was visited. Normally this means that the backup file contains the contents from before the current editing session; however, if you kill the buffer and then visit the file again, a new backup file will be made by the next save.

You can also explicitly request making another backup file from a buffer even though it has already been saved at least once. If you save the buffer with C-u C-x C-s, the version thus saved will be made into a backup file if you save the buffer again. C-u C-u C-x C-s saves the buffer, but first makes the previous file contents into a new backup file. C-u C-u C-u C-x C-s does both things: it makes a backup from the previous contents, and arranges to make another from the newly saved contents if you save again.

Next: , Up: Backup Single or Numbered Backups

If you choose to have a single backup file (this is the default), the backup file's name is normally constructed by appending ‘~’ to the file name being edited; thus, the backup file for eval.c would be eval.c~.

You can change this behavior by defining the variable make-backup-file-name-function to a suitable function. Alternatively you can customize the variable backup-directory-alist to specify that files matching certain patterns should be backed up in specific directories.

A typical use is to add an element ("." . dir) to make all backups in the directory with absolute name dir; Emacs modifies the backup file names to avoid clashes between files with the same names originating in different directories. Alternatively, adding, say, ("." . ".~") would make backups in the invisible subdirectory .~ of the original file's directory. Emacs creates the directory, if necessary, to make the backup.

If access control stops Emacs from writing backup files under the usual names, it writes the backup file as %backup%~ in your home directory. Only one such file can exist, so only the most recently made such backup is available.

If you choose to have a series of numbered backup files, backup file names contain ‘.~’, the number, and another ‘~’ after the original file name. Thus, the backup files of eval.c would be called eval.c.~1~, eval.c.~2~, and so on, all the way through names like eval.c.~259~ and beyond. The variable backup-directory-alist applies to numbered backups just as usual.

The choice of single backup or numbered backups is controlled by the variable version-control. Its possible values are

Make numbered backups.
Make numbered backups for files that have numbered backups already. Otherwise, make single backups.
Never make numbered backups; always make single backups.

You can set version-control locally in an individual buffer to control the making of backups for that buffer's file. For example, Rmail mode locally sets version-control to never to make sure that there is only one backup for an Rmail file. See Locals.

If you set the environment variable VERSION_CONTROL, to tell various GNU utilities what to do with backup files, Emacs also obeys the environment variable by setting the Lisp variable version-control accordingly at startup. If the environment variable's value is ‘t’ or ‘numbered’, then version-control becomes t; if the value is ‘nil’ or ‘existing’, then version-control becomes nil; if it is ‘never’ or ‘simple’, then version-control becomes never.

Next: , Previous: Backup Names, Up: Backup Automatic Deletion of Backups

To prevent excessive consumption of disk space, Emacs can delete numbered backup versions automatically. Generally Emacs keeps the first few backups and the latest few backups, deleting any in between. This happens every time a new backup is made.

The two variables kept-old-versions and kept-new-versions control this deletion. Their values are, respectively, the number of oldest (lowest-numbered) backups to keep and the number of newest (highest-numbered) ones to keep, each time a new backup is made. The backups in the middle (excluding those oldest and newest) are the excess middle versions—those backups are deleted. These variables' values are used when it is time to delete excess versions, just after a new backup version is made; the newly made backup is included in the count in kept-new-versions. By default, both variables are 2.

If delete-old-versions is t, Emacs deletes the excess backup files silently. If it is nil, the default, Emacs asks you whether it should delete the excess backup versions. If it has any other value, then Emacs never automatically deletes backups.

Dired's . (Period) command can also be used to delete old versions. See Dired Deletion.

Previous: Backup Deletion, Up: Backup Copying vs. Renaming

Backup files can be made by copying the old file or by renaming it. This makes a difference when the old file has multiple names (hard links). If the old file is renamed into the backup file, then the alternate names become names for the backup file. If the old file is copied instead, then the alternate names remain names for the file that you are editing, and the contents accessed by those names will be the new contents.

The method of making a backup file may also affect the file's owner and group. If copying is used, these do not change. If renaming is used, you become the file's owner, and the file's group becomes the default (different operating systems have different defaults for the group).

Having the owner change is usually a good idea, because then the owner always shows who last edited the file. Also, the owners of the backups show who produced those versions. Occasionally there is a file whose owner should not change; it is a good idea for such files to contain local variable lists to set backup-by-copying-when-mismatch locally (see File Variables).

The choice of renaming or copying is controlled by four variables. Renaming is the default choice. If the variable backup-by-copying is non-nil, copying is used. Otherwise, if the variable backup-by-copying-when-linked is non-nil, then copying is used for files that have multiple names, but renaming may still be used when the file being edited has only one name. If the variable backup-by-copying-when-mismatch is non-nil, then copying is used if renaming would cause the file's owner or group to change. backup-by-copying-when-mismatch is t by default if you start Emacs as the superuser. The fourth variable, backup-by-copying-when-privileged-mismatch, gives the highest numeric user-id for which backup-by-copying-when-mismatch will be forced on. This is useful when low-numbered user-ids are assigned to special system users, such as root, bin, daemon, etc., which must maintain ownership of files.

When a file is managed with a version control system (see Version Control), Emacs does not normally make backups in the usual way for that file. But check-in and check-out are similar in some ways to making backups. One unfortunate similarity is that these operations typically break hard links, disconnecting the file name you visited from any alternate names for the same file. This has nothing to do with Emacs—the version control system does it.

Next: , Previous: Backup, Up: Saving

23.3.3 Customizing Saving of Files

If the value of the variable require-final-newline is t, saving or writing a file silently puts a newline at the end if there isn't already one there. If the value is visit, Emacs adds a newline at the end of any file that doesn't have one, just after it visits the file. (This marks the buffer as modified, and you can undo it.) If the value is visit-save, that means to add newlines both on visiting and on saving. If the value is nil, Emacs leaves the end of the file unchanged; if it's neither nil nor t, Emacs asks you whether to add a newline. The default is nil.

Many major modes are designed for specific kinds of files that are always supposed to end in newlines. These major modes set the variable require-final-newline according to mode-require-final-newline. By setting the latter variable, you can control how these modes handle final newlines.

When Emacs saves a file, it invokes the fsync system call to force the data immediately out to disk. This is important for safety if the system crashes or in case of power outage. However, it can be disruptive on laptops using power saving, because it requires the disk to spin up each time you save a file. Setting write-region-inhibit-fsync to a non-nil value disables this synchronization. Be careful—this means increased risk of data loss.

Next: , Previous: Customize Save, Up: Saving

23.3.4 Protection against Simultaneous Editing

Simultaneous editing occurs when two users visit the same file, both make changes, and then both save them. If nobody were informed that this was happening, whichever user saved first would later find that his changes were lost.

On some systems, Emacs notices immediately when the second user starts to change the file, and issues an immediate warning. On all systems, Emacs checks when you save the file, and warns if you are about to overwrite another user's changes. You can prevent loss of the other user's work by taking the proper corrective action instead of saving the file.

When you make the first modification in an Emacs buffer that is visiting a file, Emacs records that the file is locked by you. (It does this by creating a symbolic link in the same directory with a different name.) Emacs removes the lock when you save the changes. The idea is that the file is locked whenever an Emacs buffer visiting it has unsaved changes.

If you begin to modify the buffer while the visited file is locked by someone else, this constitutes a collision. When Emacs detects a collision, it asks you what to do, by calling the Lisp function ask-user-about-lock. You can redefine this function for the sake of customization. The standard definition of this function asks you a question and accepts three possible answers:

Steal the lock. Whoever was already changing the file loses the lock, and you gain the lock.
Proceed. Go ahead and edit the file despite its being locked by someone else.
Quit. This causes an error (file-locked), and the buffer contents remain unchanged—the modification you were trying to make does not actually take place.

Note that locking works on the basis of a file name; if a file has multiple names, Emacs does not realize that the two names are the same file and cannot prevent two users from editing it simultaneously under different names. However, basing locking on names means that Emacs can interlock the editing of new files that will not really exist until they are saved.

Some systems are not configured to allow Emacs to make locks, and there are cases where lock files cannot be written. In these cases, Emacs cannot detect trouble in advance, but it still can detect the collision when you try to save a file and overwrite someone else's changes.

If Emacs or the operating system crashes, this may leave behind lock files which are stale, so you may occasionally get warnings about spurious collisions. When you determine that the collision is spurious, just use p to tell Emacs to go ahead anyway.

Every time Emacs saves a buffer, it first checks the last-modification date of the existing file on disk to verify that it has not changed since the file was last visited or saved. If the date does not match, it implies that changes were made in the file in some other way, and these changes are about to be lost if Emacs actually does save. To prevent this, Emacs displays a warning message and asks for confirmation before saving. Occasionally you will know why the file was changed and know that it does not matter; then you can answer yes and proceed. Otherwise, you should cancel the save with C-g and investigate the situation.

The first thing you should do when notified that simultaneous editing has already taken place is to list the directory with C-u C-x C-d (see Directories). This shows the file's current author. You should attempt to contact him to warn him not to continue editing. Often the next step is to save the contents of your Emacs buffer under a different name, and use diff to compare the two files.

Next: , Previous: Interlocking, Up: Saving

23.3.5 Shadowing Files

M-x shadow-initialize
Set up file shadowing.
M-x shadow-define-literal-group
Declare a single file to be shared between sites.
M-x shadow-define-regexp-group
Make all files that match each of a group of files be shared between hosts.
M-x shadow-define-cluster <RET> name <RET>
Define a shadow file cluster name.
M-x shadow-copy-files
Copy all pending shadow files.
M-x shadow-cancel
Cancel the instruction to shadow some files.

You can arrange to keep identical shadow copies of certain files in more than one place—possibly on different machines. To do this, first you must set up a shadow file group, which is a set of identically-named files shared between a list of sites. The file group is permanent and applies to further Emacs sessions as well as the current one. Once the group is set up, every time you exit Emacs, it will copy the file you edited to the other files in its group. You can also do the copying without exiting Emacs, by typing M-x shadow-copy-files.

To set up a shadow file group, use M-x shadow-define-literal-group or M-x shadow-define-regexp-group. See their documentation strings for further information.

Before copying a file to its shadows, Emacs asks for confirmation. You can answer “no” to bypass copying of this file, this time. If you want to cancel the shadowing permanently for a certain file, use M-x shadow-cancel to eliminate or change the shadow file group.

A shadow cluster is a group of hosts that share directories, so that copying to or from one of them is sufficient to update the file on all of them. Each shadow cluster has a name, and specifies the network address of a primary host (the one we copy files to), and a regular expression that matches the host names of all the other hosts in the cluster. You can define a shadow cluster with M-x shadow-define-cluster.

Previous: File Shadowing, Up: Saving

23.3.6 Updating Time Stamps Automatically

You can arrange to put a time stamp in a file, so that it will be updated automatically each time you edit and save the file. The time stamp has to be in the first eight lines of the file, and you should insert it like this:

     Time-stamp: <>

or like this:

     Time-stamp: " "

Then add the hook function time-stamp to the hook before-save-hook; that hook function will automatically update the time stamp, inserting the current date and time when you save the file. You can also use the command M-x time-stamp to update the time stamp manually. For other customizations, see the Custom group time-stamp. Note that non-numeric fields in the time stamp are formatted according to your locale setting (see Environment).

Next: , Previous: Saving, Up: Files

23.4 Reverting a Buffer

If you have made extensive changes to a file and then change your mind about them, you can get rid of them by reading in the previous version of the file. To do this, use M-x revert-buffer, which operates on the current buffer. Since reverting a buffer unintentionally could lose a lot of work, you must confirm this command with yes.

revert-buffer tries to position point in such a way that, if the file was edited only slightly, you will be at approximately the same piece of text after reverting as before. However, if you have made drastic changes, point may wind up in a totally different piece of text.

Reverting marks the buffer as “not modified” until another change is made.

Some kinds of buffers whose contents reflect data bases other than files, such as Dired buffers, can also be reverted. For them, reverting means recalculating their contents from the appropriate data base. Buffers created explicitly with C-x b cannot be reverted; revert-buffer reports an error when asked to do so.

When you edit a file that changes automatically and frequently—for example, a log of output from a process that continues to run—it may be useful for Emacs to revert the file without querying you, whenever you visit the file again with C-x C-f.

To request this behavior, set the variable revert-without-query to a list of regular expressions. When a file name matches one of these regular expressions, find-file and revert-buffer will revert it automatically if it has changed—provided the buffer itself is not modified. (If you have edited the text, it would be wrong to discard your changes.)

You may find it useful to have Emacs revert files automatically when they change. Three minor modes are available to do this.

M-x global-auto-revert-mode runs Global Auto-Revert mode, which periodically checks all file buffers and reverts when the corresponding file has changed. M-x auto-revert-mode runs a local version, Auto-Revert mode, which applies only to the buffer in which it was activated. Auto-Revert mode can be used to “tail” a file, such as a system log, so that changes made to that file by other programs are continuously displayed. To do this, just move the point to the end of the buffer, and it will stay there as the file contents change. However, if you are sure that the file will only change by growing at the end, you can tail the file more efficiently using Auto-Revert Tail mode, M-x auto-revert-tail-mode.

The variable auto-revert-interval controls how often to check for a changed file. Since checking a remote file is too slow, these modes do not check or revert remote files.

See VC Mode Line, for Auto Revert peculiarities in buffers that visit files under version control.

Next: , Previous: Reverting, Up: Files

23.5 Auto-Saving: Protection Against Disasters

Emacs saves all the visited files from time to time (based on counting your keystrokes) without being asked. This is called auto-saving. It prevents you from losing more than a limited amount of work if the system crashes.

When Emacs determines that it is time for auto-saving, each buffer is considered, and is auto-saved if auto-saving is turned on for it and it has been changed since the last time it was auto-saved. The message ‘Auto-saving...’ is displayed in the echo area during auto-saving, if any files are actually auto-saved. Errors occurring during auto-saving are caught so that they do not interfere with the execution of commands you have been typing.

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23.5.1 Auto-Save Files

Auto-saving does not normally save in the files that you visited, because it can be very undesirable to save a program that is in an inconsistent state when you have made half of a planned change. Instead, auto-saving is done in a different file called the auto-save file, and the visited file is changed only when you request saving explicitly (such as with C-x C-s).

Normally, the auto-save file name is made by appending ‘#’ to the front and rear of the visited file name. Thus, a buffer visiting file foo.c is auto-saved in a file #foo.c#. Most buffers that are not visiting files are auto-saved only if you request it explicitly; when they are auto-saved, the auto-save file name is made by appending ‘#’ to the front and rear of buffer name, then adding digits and letters at the end for uniqueness. For example, the ‘*mail*’ buffer in which you compose messages to be sent might be auto-saved in a file named #*mail*#704juu. Auto-save file names are made this way unless you reprogram parts of Emacs to do something different (the functions make-auto-save-file-name and auto-save-file-name-p). The file name to be used for auto-saving in a buffer is calculated when auto-saving is turned on in that buffer.

The variable auto-save-file-name-transforms allows a degree of control over the auto-save file name. It lets you specify a series of regular expressions and replacements to transform the auto save file name. The default value puts the auto-save files for remote files (see Remote Files) into the temporary file directory on the local machine.

When you delete a substantial part of the text in a large buffer, auto save turns off temporarily in that buffer. This is because if you deleted the text unintentionally, you might find the auto-save file more useful if it contains the deleted text. To reenable auto-saving after this happens, save the buffer with C-x C-s, or use C-u 1 M-x auto-save-mode.

If you want auto-saving to be done in the visited file rather than in a separate auto-save file, set the variable auto-save-visited-file-name to a non-nil value. In this mode, there is no real difference between auto-saving and explicit saving.

A buffer's auto-save file is deleted when you save the buffer in its visited file. To inhibit this, set the variable delete-auto-save-files to nil. Changing the visited file name with C-x C-w or set-visited-file-name renames any auto-save file to go with the new visited name.

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23.5.2 Controlling Auto-Saving

Each time you visit a file, auto-saving is turned on for that file's buffer if the variable auto-save-default is non-nil (but not in batch mode; see Entering Emacs). The default for this variable is t, so auto-saving is the usual practice for file-visiting buffers. Auto-saving can be turned on or off for any existing buffer with the command M-x auto-save-mode. Like other minor mode commands, M-x auto-save-mode turns auto-saving on with a positive argument, off with a zero or negative argument; with no argument, it toggles.

Emacs does auto-saving periodically based on counting how many characters you have typed since the last time auto-saving was done. The variable auto-save-interval specifies how many characters there are between auto-saves. By default, it is 300. Emacs doesn't accept values that are too small: if you customize auto-save-interval to a value less than 20, Emacs will behave as if the value is 20.

Auto-saving also takes place when you stop typing for a while. The variable auto-save-timeout says how many seconds Emacs should wait before it does an auto save (and perhaps also a garbage collection). (The actual time period is longer if the current buffer is long; this is a heuristic which aims to keep out of your way when you are editing long buffers, in which auto-save takes an appreciable amount of time.) Auto-saving during idle periods accomplishes two things: first, it makes sure all your work is saved if you go away from the terminal for a while; second, it may avoid some auto-saving while you are actually typing.

Emacs also does auto-saving whenever it gets a fatal error. This includes killing the Emacs job with a shell command such as ‘kill %emacs’, or disconnecting a phone line or network connection.

You can request an auto-save explicitly with the command M-x do-auto-save.

Previous: Auto Save Control, Up: Auto Save

23.5.3 Recovering Data from Auto-Saves

You can use the contents of an auto-save file to recover from a loss of data with the command M-x recover-file <RET> file <RET>. This visits file and then (after your confirmation) restores the contents from its auto-save file #file#. You can then save with C-x C-s to put the recovered text into file itself. For example, to recover file foo.c from its auto-save file #foo.c#, do:

     M-x recover-file <RET> foo.c <RET>
     yes <RET>
     C-x C-s

Before asking for confirmation, M-x recover-file displays a directory listing describing the specified file and the auto-save file, so you can compare their sizes and dates. If the auto-save file is older, M-x recover-file does not offer to read it.

If Emacs or the computer crashes, you can recover all the files you were editing from their auto save files with the command M-x recover-session. This first shows you a list of recorded interrupted sessions. Move point to the one you choose, and type C-c C-c.

Then recover-session asks about each of the files that were being edited during that session, asking whether to recover that file. If you answer y, it calls recover-file, which works in its normal fashion. It shows the dates of the original file and its auto-save file, and asks once again whether to recover that file.

When recover-session is done, the files you've chosen to recover are present in Emacs buffers. You should then save them. Only this—saving them—updates the files themselves.

Emacs records interrupted sessions for later recovery in files named ~/.emacs.d/auto-save-list/.saves-pid-hostname. All of this name except pid-hostname comes from the value of auto-save-list-file-prefix. You can record sessions in a different place by customizing that variable. If you set auto-save-list-file-prefix to nil in your .emacs file, sessions are not recorded for recovery.

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23.6 File Name Aliases

Symbolic links and hard links both make it possible for several file names to refer to the same file. Hard links are alternate names that refer directly to the file; all the names are equally valid, and no one of them is preferred. By contrast, a symbolic link is a kind of defined alias: when foo is a symbolic link to bar, you can use either name to refer to the file, but bar is the real name, while foo is just an alias. More complex cases occur when symbolic links point to directories.

If you visit two names for the same file, normally Emacs makes two different buffers, but it warns you about the situation.

Normally, if you visit a file which Emacs is already visiting under a different name, Emacs displays a message in the echo area and uses the existing buffer visiting that file. This can happen on systems that support symbolic links, or if you use a long file name on a system that truncates long file names. You can suppress the message by setting the variable find-file-suppress-same-file-warnings to a non-nil value. You can disable this feature entirely by setting the variable find-file-existing-other-name to nil: then if you visit the same file under two different names, you get a separate buffer for each file name.

If the variable find-file-visit-truename is non-nil, then the file name recorded for a buffer is the file's truename (made by replacing all symbolic links with their target names), rather than the name you specify. Setting find-file-visit-truename also implies the effect of find-file-existing-other-name.

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23.7 Version Control

Version control systems are packages that can record multiple versions of a source file, usually storing the unchanged parts of the file just once. Version control systems also record history information such as the creation time of each version, who created it, and a description of what was changed in that version.

The Emacs version control interface is called VC. Its commands work with different version control systems—currently, it supports CVS, GNU Arch, RCS, Meta-CVS, Subversion, and SCCS. Of these, the GNU project distributes CVS, GNU Arch, and RCS; we recommend that you use either CVS or GNU Arch for your projects, and RCS for individual files. We also have free software to replace SCCS, known as CSSC; if you are using SCCS and don't want to make the incompatible change to RCS or CVS, you can switch to CSSC.

VC is enabled by default in Emacs. To disable it, set the customizable variable vc-handled-backends to nil (see Customizing VC).

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23.7.1 Introduction to Version Control

VC allows you to use a version control system from within Emacs, integrating the version control operations smoothly with editing. VC provides a uniform interface to version control, so that regardless of which version control system is in use, you can use it the same way.

This section provides a general overview of version control, and describes the version control systems that VC supports. You can skip this section if you are already familiar with the version control system you want to use.

Next: , Up: Introduction to VC Supported Version Control Systems

VC currently works with six different version control systems or “back ends”: CVS, GNU Arch, RCS, Meta-CVS, Subversion, and SCCS.

CVS is a free version control system that is used for the majority of free software projects today. It allows concurrent multi-user development either locally or over the network. Some of its shortcomings, corrected by newer systems such as GNU Arch, are that it lacks atomic commits or support for renaming files. VC supports all basic editing operations under CVS, but for some less common tasks you still need to call CVS from the command line. Note also that before using CVS you must set up a repository, which is a subject too complex to treat here.

GNU Arch is a new version control system that is designed for distributed work. It differs in many ways from old well-known systems, such as CVS and RCS. It supports different transports for interoperating between users, offline operations, and it has good branching and merging features. It also supports atomic commits, and history of file renaming and moving. VC does not support all operations provided by GNU Arch, so you must sometimes invoke it from the command line, or use a specialized module.

RCS is the free version control system around which VC was initially built. The VC commands are therefore conceptually closest to RCS. Almost everything you can do with RCS can be done through VC. You cannot use RCS over the network though, and it only works at the level of individual files, rather than projects. You should use it if you want a simple, yet reliable tool for handling individual files.

Subversion is a free version control system designed to be similar to CVS but without CVS's problems. Subversion supports atomic commits, and versions directories, symbolic links, meta-data, renames, copies, and deletes. It can be used via http or via its own protocol.

Meta-CVS is another attempt to solve problems arising in CVS. It supports directory structure versioning, improved branching and merging, and use of symbolic links and meta-data in repositories.

SCCS is a proprietary but widely used version control system. In terms of capabilities, it is the weakest of the six that VC supports. VC compensates for certain features missing in SCCS (snapshots, for example) by implementing them itself, but some other VC features, such as multiple branches, are not available with SCCS. You should use SCCS only if for some reason you cannot use RCS, or one of the higher-level systems such as CVS or GNU Arch.

In the following, we discuss mainly RCS, SCCS and CVS. Nearly everything said about CVS applies to GNU Arch, Subversion and Meta-CVS as well.

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When a file is under version control, we also say that it is registered in the version control system. Each registered file has a corresponding master file which represents the file's present state plus its change history—enough to reconstruct the current version or any earlier version. Usually the master file also records a log entry for each version, describing in words what was changed in that version.

The file that is maintained under version control is sometimes called the work file corresponding to its master file. You edit the work file and make changes in it, as you would with an ordinary file. (With SCCS and RCS, you must lock the file before you start to edit it.) After you are done with a set of changes, you check the file in, which records the changes in the master file, along with a log entry for them.

With CVS, there are usually multiple work files corresponding to a single master file—often each user has his own copy. It is also possible to use RCS in this way, but this is not the usual way to use RCS.

A version control system typically has some mechanism to coordinate between users who want to change the same file. One method is locking (analogous to the locking that Emacs uses to detect simultaneous editing of a file, but distinct from it). The other method is to merge your changes with other people's changes when you check them in.

With version control locking, work files are normally read-only so that you cannot change them. You ask the version control system to make a work file writable for you by locking it; only one user can do this at any given time. When you check in your changes, that unlocks the file, making the work file read-only again. This allows other users to lock the file to make further changes. SCCS always uses locking, and RCS normally does.

The other alternative for RCS is to let each user modify the work file at any time. In this mode, locking is not required, but it is permitted; check-in is still the way to record a new version.

CVS normally allows each user to modify his own copy of the work file at any time, but requires merging with changes from other users at check-in time. However, CVS can also be set up to require locking. (see CVS Options).

Previous: VC Concepts, Up: Introduction to VC Types of Log File

Projects that use a revision control system can have two types of log for changes. One is the per-file log maintained by the revision control system: each time you check in a change, you must fill out a log entry for the change (see Log Buffer). This kind of log is called the version control log, also the revision control log, RCS log, or CVS log.

The other kind of log is the file ChangeLog (see Change Log). It provides a chronological record of all changes to a large portion of a program—typically one directory and its subdirectories. A small program would use one ChangeLog file; a large program may well merit a ChangeLog file in each major directory. See Change Log.

A project maintained with version control can use just the per-file log, or it can use both kinds of logs. It can handle some files one way and some files the other way. Each project has its policy, which you should follow.

When the policy is to use both, you typically want to write an entry for each change just once, then put it into both logs. You can write the entry in ChangeLog, then copy it to the log buffer when you check in the change. Or you can write the entry in the log buffer while checking in the change, and later use the C-x v a command to copy it to ChangeLog (see Change Logs and VC).

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23.7.2 Version Control and the Mode Line

When you visit a file that is under version control, Emacs indicates this on the mode line. For example, ‘RCS-1.3’ says that RCS is used for that file, and the current version is 1.3.

The character between the back-end name and the version number indicates the version control status of the file. ‘-’ means that the work file is not locked (if locking is in use), or not modified (if locking is not in use). ‘:’ indicates that the file is locked, or that it is modified. If the file is locked by some other user (for instance, ‘jim’), that is displayed as ‘RCS:jim:1.3’.

When Auto Revert mode (see Reverting) reverts a buffer that is under version control, it updates the version control information in the mode line. However, Auto Revert mode may not properly update this information if the version control status changes without changes to the work file, from outside the current Emacs session. If you set auto-revert-check-vc-info to t, Auto Revert mode updates the version control status information every auto-revert-interval seconds, even if the work file itself is unchanged. The resulting CPU usage depends on the version control system, but is usually not excessive.

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23.7.3 Basic Editing under Version Control

The principal VC command is an all-purpose command that performs either locking or check-in, depending on the situation.

C-x v v
Perform the next logical version control operation on this file.

The precise action of this command depends on the state of the file, and whether the version control system uses locking or not. SCCS and RCS normally use locking; CVS normally does not use locking.

As a special convenience that is particularly useful for files with locking, you can let Emacs check a file in or out whenever you change its read-only flag. This means, for example, that you cannot accidentally edit a file without properly checking it out first. To achieve this, bind the key C-x C-q to vc-toggle-read-only in your ~/.emacs file. (See Init Rebinding.)

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If locking is used for the file (as with SCCS, and RCS in its default mode), C-x v v can either lock a file or check it in:

These rules also apply when you use CVS in locking mode, except that there is no such thing as stealing a lock.

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When there is no locking—the default for CVS—work files are always writable; you do not need to do anything before you begin to edit a file. The status indicator on the mode line is ‘-’ if the file is unmodified; it flips to ‘:’ as soon as you save any changes in the work file.

Here is what C-x v v does when using CVS:

These rules also apply when you use RCS in the mode that does not require locking, except that automatic merging of changes from the master file is not implemented. Unfortunately, this means that nothing informs you if another user has checked in changes in the same file since you began editing it, and when this happens, his changes will be effectively removed when you check in your version (though they will remain in the master file, so they will not be entirely lost). You must therefore verify that the current version is unchanged, before you check in your changes. We hope to eliminate this risk and provide automatic merging with RCS in a future Emacs version.

In addition, locking is possible with RCS even in this mode, although it is not required; C-x v v with an unmodified file locks the file, just as it does with RCS in its normal (locking) mode.

Next: , Previous: Without Locking, Up: Basic VC Editing Advanced Control in C-x v v

When you give a prefix argument to vc-next-action (C-u C-x v v), it still performs the next logical version control operation, but accepts additional arguments to specify precisely how to do the operation.

Previous: Advanced C-x v v, Up: Basic VC Editing Features of the Log Entry Buffer

When you check in changes, C-x v v first reads a log entry. It pops up a buffer called ‘*VC-Log*’ for you to enter the log entry.

Sometimes the ‘*VC-Log*’ buffer contains default text when you enter it, typically the last log message entered. If it does, mark and point are set around the entire contents of the buffer so that it is easy to kill the contents of the buffer with C-w.

If you work by writing entries in the ChangeLog (see Change Log) and then commit the change under revision control, you can generate the Log Edit text from the ChangeLog using C-c C-a (log-edit-insert-changelog). This looks for entries for the file(s) concerned in the top entry in the ChangeLog and uses those paragraphs as the log text. This text is only inserted if the top entry was made under your user name on the current date. See Change Logs and VC, for the opposite way of working—generating ChangeLog entries from the revision control log.

In the ‘*VC-Log*’ buffer, C-c C-f (M-x log-edit-show-files) shows the list of files to be committed in case you need to check that. (This can be a list of more than one file if you use VC Dired mode or PCL-CVS. See VC Dired Mode, and About PCL-CVS.)

When you have finished editing the log message, type C-c C-c to exit the buffer and commit the change.

To abort check-in, just don't type C-c C-c in that buffer. You can switch buffers and do other editing. As long as you don't try to check in another file, the entry you were editing remains in the ‘*VC-Log*’ buffer, and you can go back to that buffer at any time to complete the check-in.

If you change several source files for the same reason, it is often convenient to specify the same log entry for many of the files. To do this, use the history of previous log entries. The commands M-n, M-p, M-s and M-r for doing this work just like the minibuffer history commands (except that these versions are used outside the minibuffer).

Each time you check in a file, the log entry buffer is put into VC Log mode, which involves running two hooks: text-mode-hook and vc-log-mode-hook. See Hooks.

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23.7.4 Examining And Comparing Old Versions

One of the convenient features of version control is the ability to examine any version of a file, or compare two versions.

C-x v ~ version <RET>
Examine version version of the visited file, in a buffer of its own.
C-x v =
Compare the current buffer contents with the latest checked-in version of the file.
C-u C-x v = file <RET> oldvers <RET> newvers <RET>
Compare the specified two versions of file.
C-x v g
Display the file with per-line version information and using colors.

To examine an old version in its entirety, visit the file and then type C-x v ~ version <RET> (vc-version-other-window). This puts the text of version version in a file named filename.~version~, and visits it in its own buffer in a separate window. (In RCS, you can also select an old version and create a branch from it. See Branches.)

It is usually more convenient to compare two versions of the file, with the command C-x v = (vc-diff). Plain C-x v = compares the current buffer contents (saving them in the file if necessary) with the last checked-in version of the file. C-u C-x v =, with a numeric argument, reads a file name and two version numbers, then compares those versions of the specified file. Both forms display the output in a special buffer in another window.

You can specify a checked-in version by its number; an empty input specifies the current contents of the work file (which may be different from all the checked-in versions). You can also specify a snapshot name (see Snapshots) instead of one or both version numbers.

If you supply a directory name instead of the name of a registered file, this command compares the two specified versions of all registered files in that directory and its subdirectories.

C-x v = works by running a variant of the diff utility designed to work with the version control system in use. When you invoke diff this way, in addition to the options specified by diff-switches (see Comparing Files), it receives those specified by vc-diff-switches, plus those specified for the specific back end by vc-backend-diff-switches. For instance, when the version control back end is RCS, diff uses the options in vc-rcs-diff-switches. The ‘vc...diff-switches’ variables are nil by default.

Unlike the M-x diff command, C-x v = does not try to locate the changes in the old and new versions. This is because normally one or both versions do not exist as files when you compare them; they exist only in the records of the master file. See Comparing Files, for more information about M-x diff.

For some backends, you can display the file annotated with per-line version information and using colors to enhance the visual appearance, with the command M-x vc-annotate. It creates a new buffer to display file's text, colored to show how old each part is. Text colored red is new, blue means old, and intermediate colors indicate intermediate ages. By default, the time scale is 360 days, so that everything more than one year old is shown in blue.

When you give a prefix argument to this command, it uses the minibuffer to read two arguments: which version number to display and annotate (instead of the current file contents), and a stretch factor for the time scale. A stretch factor of 0.1 means that the color range from red to blue spans the past 36 days instead of 360 days. A stretch factor greater than 1 means the color range spans more than a year.

From the annotate buffer, you can use the following keys to browse the annotations of past revisions, view diffs, or view log entries:

Annotate the previous revision, that is to say, the revision before the one currently annotated. A numeric prefix argument is a repeat count, so C-u 10 P would take you back 10 revisions.
Annotate the next revision—the one after the revision currently annotated. A numeric prefix argument is a repeat count.
Annotate the revision indicated by the current line.
Annotate the revision before the one indicated by the current line. This is useful to see the state the file was in before the change on the current line was made.
Display the diff between the current line's revision and the previous revision. This is useful to see what the current line's revision actually changed in the file.
Show the log of the current line's revision. This is useful to see the author's description of the changes in the revision on the current line.
Annotate the workfile version–the one you are editing. If you used P and N to browse to other revisions, use this key to return to the latest version.

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23.7.5 The Secondary Commands of VC

This section explains the secondary commands of VC; those that you might use once a day.

Next: , Up: Secondary VC Commands Registering a File for Version Control

You can put any file under version control by simply visiting it, and then typing C-x v i (vc-register).

C-x v i
Register the visited file for version control.

To register the file, Emacs must choose which version control system to use for it. If the file's directory already contains files registered in a version control system, Emacs uses that system. If there is more than one system in use for a directory, Emacs uses the one that appears first in vc-handled-backends (see Customizing VC). On the other hand, if there are no files already registered, Emacs uses the first system from vc-handled-backends that could register the file (for example, you cannot register a file under CVS if its directory is not already part of a CVS tree); with the default value of vc-handled-backends, this means that Emacs uses RCS in this situation.

If locking is in use, C-x v i leaves the file unlocked and read-only. Type C-x v v if you wish to start editing it. After registering a file with CVS, you must subsequently commit the initial version by typing C-x v v. Until you do that, the version appears as ‘@@’ in the mode line.

The initial version number for a newly registered file is 1.1, by default. You can specify a different default by setting the variable vc-default-init-version, or you can give C-x v i a numeric argument; then it reads the initial version number for this particular file using the minibuffer.

If vc-initial-comment is non-nil, C-x v i reads an initial comment to describe the purpose of this source file. Reading the initial comment works like reading a log entry (see Log Buffer).

Next: , Previous: Registering, Up: Secondary VC Commands VC Status Commands
C-x v l
Display version control state and change history.

To view the detailed version control status and history of a file, type C-x v l (vc-print-log). It displays the history of changes to the current file, including the text of the log entries. The output appears in a separate window. The point is centered at the revision of the file that is currently being visited.

From the change log buffer, the following keys are used to move between the logs of revisions and files, to view past revisions, and to view diffs:

Move to the previous revision-item in the buffer. (Revision entries in the log buffer are usually in reverse-chronological order, so the previous revision-item usually corresponds to a newer revision.) A numeric prefix argument is a repeat count.
Move to the next revision-item (which most often corresponds to the previous revision of the file). A numeric prefix argument is a repeat count.
Move to the log of the previous file, when the logs of multiple files are in the log buffer (see VC Dired Mode). Otherwise, just move to the beginning of the log. A numeric prefix argument is a repeat count, so C-u 10 P would move backward 10 files.
Move to the log of the next file, when the logs of multiple files are in the log buffer (see VC Dired Mode). It also takes a numeric prefix argument as a repeat count.
Visit the revision indicated at the current line, like typing C-x v ~ and specifying this revision's number (see Old Versions).
Display the diff (see Comparing Files) between the revision indicated at the current line and the next earlier revision. This is useful to see what actually changed when the revision indicated on the current line was committed.

Next: , Previous: VC Status, Up: Secondary VC Commands Undoing Version Control Actions
C-x v u
Revert the buffer and the file to the last checked-in version.
C-x v c
Remove the last-entered change from the master for the visited file. This undoes your last check-in.

If you want to discard your current set of changes and revert to the last version checked in, use C-x v u (vc-revert-buffer). This leaves the file unlocked; if locking is in use, you must first lock the file again before you change it again. C-x v u requires confirmation, unless it sees that you haven't made any changes since the last checked-in version.

C-x v u is also the command to unlock a file if you lock it and then decide not to change it.

To cancel a change that you already checked in, use C-x v c (vc-cancel-version). This command discards all record of the most recent checked-in version. C-x v c also offers to revert your work file and buffer to the previous version (the one that precedes the version that is deleted).

If you answer no, VC keeps your changes in the buffer, and locks the file. The no-revert option is useful when you have checked in a change and then discover a trivial error in it; you can cancel the erroneous check-in, fix the error, and check the file in again.

When C-x v c does not revert the buffer, it unexpands all version control headers in the buffer instead (see Version Headers). This is because the buffer no longer corresponds to any existing version. If you check it in again, the check-in process will expand the headers properly for the new version number.

However, it is impossible to unexpand the RCS ‘$Log$’ header automatically. If you use that header feature, you have to unexpand it by hand—by deleting the entry for the version that you just canceled.

Be careful when invoking C-x v c, as it is easy to lose a lot of work with it. To help you be careful, this command always requires confirmation with yes. Note also that this command is disabled under CVS, because canceling versions is very dangerous and discouraged with CVS.

Next: , Previous: VC Undo, Up: Secondary VC Commands Dired under VC

The VC Dired Mode described here works with all the version control systems that VC supports. Another more powerful facility, designed specifically for CVS, is called PCL-CVS. See About PCL-CVS.

When you are working on a large program, it is often useful to find out which files have changed within an entire directory tree, or to view the status of all files under version control at once, and to perform version control operations on collections of files. You can use the command C-x v d (vc-directory) to make a directory listing that includes only files relevant for version control.

C-x v d creates a buffer which uses VC Dired Mode. This looks much like an ordinary Dired buffer (see Dired); however, normally it shows only the noteworthy files (those locked or not up-to-date). This is called terse display. If you set the variable vc-dired-terse-display to nil, then VC Dired shows all relevant files—those managed under version control, plus all subdirectories (full display). The command v t in a VC Dired buffer toggles between terse display and full display (see VC Dired Commands).

By default, VC Dired produces a recursive listing of noteworthy or relevant files at or below the given directory. You can change this by setting the variable vc-dired-recurse to nil; then VC Dired shows only the files in the given directory.

The line for an individual file shows the version control state in the place of the hard link count, owner, group, and size of the file. If the file is unmodified, in sync with the master file, the version control state shown is blank. Otherwise it consists of text in parentheses. Under RCS and SCCS, the name of the user locking the file is shown; under CVS, an abbreviated version of the ‘cvs status’ output is used. Here is an example using RCS:

       -rw-r--r-- (jim)      Apr  2 23:39 file1
       -r--r--r--            Apr  5 20:21 file2

The files ‘file1’ and ‘file2’ are under version control, ‘file1’ is locked by user jim, and ‘file2’ is unlocked.

Here is an example using CVS:

       -rw-r--r-- (modified) Aug  2  1997 file1.c
       -rw-r--r--            Apr  4 20:09 file2.c
       -rw-r--r-- (merge)    Sep 13  1996 file3.c

Here ‘file1.c’ is modified with respect to the repository, and ‘file2.c’ is not. ‘file3.c’ is modified, but other changes have also been checked in to the repository—you need to merge them with the work file before you can check it in.

When VC Dired displays subdirectories (in the “full” display mode), it omits some that should never contain any files under version control. By default, this includes Version Control subdirectories such as ‘RCS’ and ‘CVS’; you can customize this by setting the variable vc-directory-exclusion-list.

You can fine-tune VC Dired's format by typing C-u C-x v d—as in ordinary Dired, that allows you to specify additional switches for the ‘ls’ command.

Previous: VC Dired Mode, Up: Secondary VC Commands VC Dired Commands

All the usual Dired commands work normally in VC Dired mode, except for v, which is redefined as the version control prefix. You can invoke VC commands such as vc-diff and vc-print-log by typing v =, or v l, and so on. Most of these commands apply to the file name on the current line.

The command v v (vc-next-action) operates on all the marked files, so that you can lock or check in several files at once. If it operates on more than one file, it handles each file according to its current state; thus, it might lock one file, but check in another file. This could be confusing; it is up to you to avoid confusing behavior by marking a set of files that are in a similar state. If no files are marked, v v operates on the file in the current line.

If any files call for check-in, v v reads a single log entry, then uses it for all the files being checked in. This is convenient for registering or checking in several files at once, as part of the same change.

You can toggle between terse display (only locked files, or files not up-to-date) and full display at any time by typing v t (vc-dired-toggle-terse-mode). There is also a special command * l (vc-dired-mark-locked), which marks all files currently locked (or, with CVS, all files not up-to-date). Thus, typing * l t k is another way to delete from the buffer all files except those currently locked.

Next: , Previous: Secondary VC Commands, Up: Version Control

23.7.6 Multiple Branches of a File

One use of version control is to maintain multiple “current” versions of a file. For example, you might have different versions of a program in which you are gradually adding various unfinished new features. Each such independent line of development is called a branch. VC allows you to create branches, switch between different branches, and merge changes from one branch to another. Please note, however, that branches are not supported for SCCS.

A file's main line of development is usually called the trunk. The versions on the trunk are normally numbered 1.1, 1.2, 1.3, etc. At any such version, you can start an independent branch. A branch starting at version 1.2 would have version number, and consecutive versions on this branch would have numbers,,, and so on. If there is a second branch also starting at version 1.2, it would consist of versions,,, etc.

If you omit the final component of a version number, that is called a branch number. It refers to the highest existing version on that branch—the head version of that branch. The branches in the example above have branch numbers 1.2.1 and 1.2.2.

Next: , Up: Branches Switching between Branches

To switch between branches, type C-u C-x v v and specify the version number you want to select. This version is then visited unlocked (write-protected), so you can examine it before locking it. Switching branches in this way is allowed only when the file is not locked.

You can omit the minor version number, thus giving only the branch number; this takes you to the head version on the chosen branch. If you only type <RET>, Emacs goes to the highest version on the trunk.

After you have switched to any branch (including the main branch), you stay on it for subsequent VC commands, until you explicitly select some other branch.

Next: , Previous: Switching Branches, Up: Branches Creating New Branches

To create a new branch from a head version (one that is the latest in the branch that contains it), first select that version if necessary, lock it with C-x v v, and make whatever changes you want. Then, when you check in the changes, use C-u C-x v v. This lets you specify the version number for the new version. You should specify a suitable branch number for a branch starting at the current version. For example, if the current version is 2.5, the branch number should be 2.5.1, 2.5.2, and so on, depending on the number of existing branches at that point.

To create a new branch at an older version (one that is no longer the head of a branch), first select that version (see Switching Branches), then lock it with C-x v v. You'll be asked to confirm, when you lock the old version, that you really mean to create a new branch—if you say no, you'll be offered a chance to lock the latest version instead.

Then make your changes and type C-x v v again to check in a new version. This automatically creates a new branch starting from the selected version. You need not specially request a new branch, because that's the only way to add a new version at a point that is not the head of a branch.

After the branch is created, you “stay” on it. That means that subsequent check-ins create new versions on that branch. To leave the branch, you must explicitly select a different version with C-u C-x v v. To transfer changes from one branch to another, use the merge command, described in the next section.

Next: , Previous: Creating Branches, Up: Branches Merging Branches

When you have finished the changes on a certain branch, you will often want to incorporate them into the file's main line of development (the trunk). This is not a trivial operation, because development might also have proceeded on the trunk, so that you must merge the changes into a file that has already been changed otherwise. VC allows you to do this (and other things) with the vc-merge command.

C-x v m (vc-merge)
Merge changes into the work file.

C-x v m (vc-merge) takes a set of changes and merges it into the current version of the work file. It firsts asks you in the minibuffer where the changes should come from. If you just type <RET>, Emacs merges any changes that were made on the same branch since you checked the file out (we call this merging the news). This is the common way to pick up recent changes from the repository, regardless of whether you have already changed the file yourself.

You can also enter a branch number or a pair of version numbers in the minibuffer. Then C-x v m finds the changes from that branch, or the differences between the two versions you specified, and merges them into the current version of the current file.

As an example, suppose that you have finished a certain feature on branch 1.3.1. In the meantime, development on the trunk has proceeded to version 1.5. To merge the changes from the branch to the trunk, first go to the head version of the trunk, by typing C-u C-x v v <RET>. Version 1.5 is now current. If locking is used for the file, type C-x v v to lock version 1.5 so that you can change it. Next, type C-x v m 1.3.1 <RET>. This takes the entire set of changes on branch 1.3.1 (relative to version 1.3, where the branch started, up to the last version on the branch) and merges it into the current version of the work file. You can now check in the changed file, thus creating version 1.6 containing the changes from the branch.

It is possible to do further editing after merging the branch, before the next check-in. But it is usually wiser to check in the merged version, then lock it and make the further changes. This will keep a better record of the history of changes.

When you merge changes into a file that has itself been modified, the changes might overlap. We call this situation a conflict, and reconciling the conflicting changes is called resolving a conflict.

Whenever conflicts occur during merging, VC detects them, tells you about them in the echo area, and asks whether you want help in merging. If you say yes, it starts an Ediff session (see Ediff).

If you say no, the conflicting changes are both inserted into the file, surrounded by conflict markers. The example below shows how a conflict region looks; the file is called ‘name’ and the current master file version with user B's changes in it is 1.11.

     <<<<<<< name
       User A's version
       User B's version
     >>>>>>> 1.11

Then you can resolve the conflicts by editing the file manually. Or you can type M-x vc-resolve-conflicts after visiting the file. This starts an Ediff session, as described above. Don't forget to check in the merged version afterwards.

Previous: Merging, Up: Branches Multi-User Branching

It is often useful for multiple developers to work simultaneously on different branches of a file. CVS allows this by default; for RCS, it is possible if you create multiple source directories. Each source directory should have a link named RCS which points to a common directory of RCS master files. Then each source directory can have its own choice of selected versions, but all share the same common RCS records.

This technique works reliably and automatically, provided that the source files contain RCS version headers (see Version Headers). The headers enable Emacs to be sure, at all times, which version number is present in the work file.

If the files do not have version headers, you must instead tell Emacs explicitly in each session which branch you are working on. To do this, first find the file, then type C-u C-x v v and specify the correct branch number. This ensures that Emacs knows which branch it is using during this particular editing session.

Next: , Previous: Branches, Up: Version Control

23.7.7 Remote Repositories

A common way of using CVS is to set up a central CVS repository on some Internet host, then have each developer check out a personal working copy of the files on his local machine. Committing changes to the repository, and picking up changes from other users into one's own working area, then works by direct interactions with the CVS server.

One difficulty is that access to the CVS server is often slow, and that developers might need to work off-line as well. VC is designed to reduce the amount of network interaction necessary.

Next: , Up: Remote Repositories Version Backups

When VC sees that the CVS repository for a file is on a remote machine, it automatically makes local backups of unmodified versions of the file—automatic version backups. This means that you can compare the file to the repository version (C-x v =), or revert to that version (C-x v u), without any network interactions.

The local copy of the unmodified file is called a version backup to indicate that it corresponds exactly to a version that is stored in the repository. Note that version backups are not the same as ordinary Emacs backup files (see Backup). But they follow a similar naming convention.

For a file that comes from a remote CVS repository, VC makes a version backup whenever you save the first changes to the file, and removes it after you have committed your modified version to the repository. You can disable the making of automatic version backups by setting vc-cvs-stay-local to nil (see CVS Options).

The name of the automatic version backup for version version of file file is file.~version.~. This is almost the same as the name used by C-x v ~ (see Old Versions), the only difference being the additional dot (‘.’) after the version number. This similarity is intentional, because both kinds of files store the same kind of information. The file made by C-x v ~ acts as a manual version backup.

All the VC commands that operate on old versions of a file can use both kinds of version backups. For instance, C-x v ~ uses either an automatic or a manual version backup, if possible, to get the contents of the version you request. Likewise, C-x v = and C-x v u use either an automatic or a manual version backup, if one of them exists, to get the contents of a version to compare or revert to. If you changed a file outside of Emacs, so that no automatic version backup was created for the previous text, you can create a manual backup of that version using C-x v ~, and thus obtain the benefit of the local copy for Emacs commands.

The only difference in Emacs's handling of manual and automatic version backups, once they exist, is that Emacs deletes automatic version backups when you commit to the repository. By contrast, manual version backups remain until you delete them.

Previous: Version Backups, Up: Remote Repositories Local Version Control

When you make many changes to a file that comes from a remote repository, it can be convenient to have version control on your local machine as well. You can then record intermediate versions, revert to a previous state, etc., before you actually commit your changes to the remote server.

VC lets you do this by putting a file under a second, local version control system, so that the file is effectively registered in two systems at the same time. For the description here, we will assume that the remote system is CVS, and you use RCS locally, although the mechanism works with any combination of version control systems (back ends).

To make it work with other back ends, you must make sure that the “more local” back end comes before the “more remote” back end in the setting of vc-handled-backends (see Customizing VC). By default, this variable is set up so that you can use remote CVS and local RCS as described here.

To start using local RCS for a file that comes from a remote CVS server, you must register the file in RCS, by typing C-u C-x v v rcs <RET>. (In other words, use vc-next-action with a prefix argument, and specify RCS as the back end.)

You can do this at any time; it does not matter whether you have already modified the file with respect to the version in the CVS repository. If possible, VC tries to make the RCS master start with the unmodified repository version, then checks in any local changes as a new version. This works if you have not made any changes yet, or if the unmodified repository version exists locally as a version backup (see Version Backups). If the unmodified version is not available locally, the RCS master starts with the modified version; the only drawback to this is that you cannot compare your changes locally to what is stored in the repository.

The version number of the RCS master is derived from the current CVS version, starting a branch from it. For example, if the current CVS version is 1.23, the local RCS branch will be 1.23.1. Version 1.23 in the RCS master will be identical to version 1.23 under CVS; your first changes are checked in as (If the unmodified file is not available locally, VC will check in the modified file twice, both as 1.23 and, to make the revision numbers consistent.)

If you do not use locking under CVS (the default), locking is also disabled for RCS, so that editing under RCS works exactly as under CVS.

When you are done with local editing, you can commit the final version back to the CVS repository by typing C-u C-x v v cvs <RET>. This initializes the log entry buffer (see Log Buffer) to contain all the log entries you have recorded in the RCS master; you can edit them as you wish, and then commit in CVS by typing C-c C-c. If the commit is successful, VC removes the RCS master, so that the file is once again registered under CVS only. (The RCS master is not actually deleted, just renamed by appending ‘~’ to the name, so that you can refer to it later if you wish.)

While using local RCS, you can pick up recent changes from the CVS repository into your local file, or commit some of your changes back to CVS, without terminating local RCS version control. To do this, switch to the CVS back end temporarily, with the C-x v b command:

C-x v b
Switch to another back end that the current file is registered under (vc-switch-backend).
C-u C-x v b backend <RET>
Switch to backend for the current file.

C-x v b does not change the buffer contents, or any files; it only changes VC's perspective on how to handle the file. Any subsequent VC commands for that file will operate on the back end that is currently selected.

If the current file is registered in more than one back end, typing C-x v b “cycles” through all of these back ends. With a prefix argument, it asks for the back end to use in the minibuffer.

Thus, if you are using local RCS, and you want to pick up some recent changes in the file from remote CVS, first visit the file, then type C-x v b to switch to CVS, and finally use C-x v m <RET> to merge the news (see Merging). You can then switch back to RCS by typing C-x v b again, and continue to edit locally.

But if you do this, the revision numbers in the RCS master no longer correspond to those of CVS. Technically, this is not a problem, but it can become difficult to keep track of what is in the CVS repository and what is not. So we suggest that you return from time to time to CVS-only operation, by committing your local changes back to the repository using C-u C-x v v cvs <RET>.

Next: , Previous: Remote Repositories, Up: Version Control

23.7.8 Snapshots

A snapshot is a named set of file versions (one for each registered file) that you can treat as a unit. One important kind of snapshot is a release, a (theoretically) stable version of the system that is ready for distribution to users.

Next: , Up: Snapshots Making and Using Snapshots

There are two basic commands for snapshots; one makes a snapshot with a given name, the other retrieves a named snapshot.

C-x v s name <RET>
Define the last saved versions of every registered file in or under the current directory as a snapshot named name (vc-create-snapshot).

C-x v r name <RET>
For all registered files at or below the current directory level, select whatever versions correspond to the snapshot name (vc-retrieve-snapshot).

This command reports an error if any files are locked at or below the current directory, without changing anything; this is to avoid overwriting work in progress.

A snapshot uses a very small amount of resources—just enough to record the list of file names and which version belongs to the snapshot. Thus, you need not hesitate to create snapshots whenever they are useful.

You can give a snapshot name as an argument to C-x v = or C-x v ~ (see Old Versions). Thus, you can use it to compare a snapshot against the current files, or two snapshots against each other, or a snapshot against a named version.

Previous: Making Snapshots, Up: Snapshots Snapshot Caveats

VC's snapshot facilities are modeled on RCS's named-configuration support. They use RCS's native facilities for this, so under VC snapshots made using RCS are visible even when you bypass VC.

For SCCS, VC implements snapshots itself. The files it uses contain name/file/version-number triples. These snapshots are visible only through VC.

A snapshot is a set of checked-in versions. So make sure that all the files are checked in and not locked when you make a snapshot.

File renaming and deletion can create some difficulties with snapshots. This is not a VC-specific problem, but a general design issue in version control systems that no one has solved very well yet.

If you rename a registered file, you need to rename its master along with it (the command vc-rename-file does this automatically). If you are using SCCS, you must also update the records of the snapshot, to mention the file by its new name (vc-rename-file does this, too). An old snapshot that refers to a master file that no longer exists under the recorded name is invalid; VC can no longer retrieve it. It would be beyond the scope of this manual to explain enough about RCS and SCCS to explain how to update the snapshots by hand.

Using vc-rename-file makes the snapshot remain valid for retrieval, but it does not solve all problems. For example, some of the files in your program probably refer to others by name. At the very least, the makefile probably mentions the file that you renamed. If you retrieve an old snapshot, the renamed file is retrieved under its new name, which is not the name that the makefile expects. So the program won't really work as retrieved.

Next: , Previous: Snapshots, Up: Version Control

23.7.9 Miscellaneous Commands and Features of VC

This section explains the less-frequently-used features of VC.

Next: , Up: Miscellaneous VC Change Logs and VC

If you use RCS or CVS for a program and also maintain a change log file for it (see Change Log), you can generate change log entries automatically from the version control log entries:

C-x v a
Visit the current directory's change log file and, for registered files in that directory, create new entries for versions checked in since the most recent entry in the change log file. (vc-update-change-log).

This command works with RCS or CVS only, not with SCCS.

C-u C-x v a
As above, but only find entries for the current buffer's file.
M-1 C-x v a
As above, but find entries for all the currently visited files that are maintained with version control. This works only with RCS, and it puts all entries in the log for the default directory, which may not be appropriate.

For example, suppose the first line of ChangeLog is dated 1999-04-10, and that the only check-in since then was by Nathaniel Bowditch to rcs2log on 1999-05-22 with log text ‘Ignore log messages that start with `#'.’. Then C-x v a visits ChangeLog and inserts text like this:

     1999-05-22  Nathaniel Bowditch  <>
             * rcs2log: Ignore log messages that start with `#'.

You can then edit the new change log entry further as you wish.

Some of the new change log entries may duplicate what's already in ChangeLog. You will have to remove these duplicates by hand.

Normally, the log entry for file foo is displayed as ‘* foo: text of log entry’. The ‘:’ after foo is omitted if the text of the log entry starts with ‘(functionname): . For example, if the log entry for vc.el is ‘(vc-do-command): Check call-process status.’, then the text in ChangeLog looks like this:

     1999-05-06  Nathaniel Bowditch  <>
             * vc.el (vc-do-command): Check call-process status.

When C-x v a adds several change log entries at once, it groups related log entries together if they all are checked in by the same author at nearly the same time. If the log entries for several such files all have the same text, it coalesces them into a single entry. For example, suppose the most recent check-ins have the following log entries:

• For vc.texinfo: ‘Fix expansion typos.’ • For vc.el: ‘Don't call expand-file-name.’ • For vc-hooks.el: ‘Don't call expand-file-name.

They appear like this in ChangeLog:

     1999-04-01  Nathaniel Bowditch  <>
             * vc.texinfo: Fix expansion typos.
             * vc.el, vc-hooks.el: Don't call expand-file-name.

Normally, C-x v a separates log entries by a blank line, but you can mark several related log entries to be clumped together (without an intervening blank line) by starting the text of each related log entry with a label of the form ‘{clumpname. The label itself is not copied to ChangeLog. For example, suppose the log entries are:

• For vc.texinfo: ‘{expand} Fix expansion typos.’ • For vc.el: ‘{expand} Don't call expand-file-name.’ • For vc-hooks.el: ‘{expand} Don't call expand-file-name.

Then the text in ChangeLog looks like this:

     1999-04-01  Nathaniel Bowditch  <>
             * vc.texinfo: Fix expansion typos.
             * vc.el, vc-hooks.el: Don't call expand-file-name.

A log entry whose text begins with ‘#’ is not copied to ChangeLog. For example, if you merely fix some misspellings in comments, you can log the change with an entry beginning with ‘#’ to avoid putting such trivia into ChangeLog.

Next: , Previous: Change Logs and VC, Up: Miscellaneous VC Renaming VC Work Files and Master Files

When you rename a registered file, you must also rename its master file correspondingly to get proper results. Use vc-rename-file to rename the source file as you specify, and rename its master file accordingly. It also updates any snapshots (see Snapshots) that mention the file, so that they use the new name; despite this, the snapshot thus modified may not completely work (see Snapshot Caveats).

Some backends do not provide an explicit rename operation to their repositories. After issuing vc-rename-file, use C-x v v on the original and renamed buffers and provide the necessary edit log.

You cannot use vc-rename-file on a file that is locked by someone else.

Previous: Renaming and VC, Up: Miscellaneous VC Inserting Version Control Headers

Sometimes it is convenient to put version identification strings directly into working files. Certain special strings called version headers are replaced in each successive version by the number of that version.

If you are using RCS, and version headers are present in your working files, Emacs can use them to determine the current version and the locking state of the files. This is more reliable than referring to the master files, which is done when there are no version headers. Note that in a multi-branch environment, version headers are necessary to make VC behave correctly (see Multi-User Branching).

Searching for version headers is controlled by the variable vc-consult-headers. If it is non-nil (the default), Emacs searches for headers to determine the version number you are editing. Setting it to nil disables this feature.

You can use the C-x v h command (vc-insert-headers) to insert a suitable header string.

C-x v h
Insert headers in a file for use with your version-control system.

The default header string is ‘$Id$’ for RCS and ‘%W%’ for SCCS. You can specify other headers to insert by setting the variables vc-backend-header where backend is rcs or sccs.

Instead of a single string, you can specify a list of strings; then each string in the list is inserted as a separate header on a line of its own.

It is often necessary to use “superfluous” backslashes when writing the strings that you put in this variable. For instance, you might write "$Id\$" rather than "$Id$". The extra backslash prevents the string constant from being interpreted as a header, if the Emacs Lisp file containing it is maintained with version control.

Each header is inserted surrounded by tabs, inside comment delimiters, on a new line at point. Normally the ordinary comment start and comment end strings of the current mode are used, but for certain modes, there are special comment delimiters for this purpose; the variable vc-comment-alist specifies them. Each element of this list has the form (mode starter ender).

The variable vc-static-header-alist specifies further strings to add based on the name of the buffer. Its value should be a list of elements of the form (regexp . format). Whenever regexp matches the buffer name, format is inserted as part of the header. A header line is inserted for each element that matches the buffer name, and for each string specified by vc-backend-header. The header line is made by processing the string from vc-backend-header with the format taken from the element. The default value for vc-static-header-alist is as follows:

     (("\\.c$" .
       "\n#ifndef lint\nstatic char vcid[] = \"\%s\";\n\
     #endif /* lint */\n"))

It specifies insertion of text of this form:

     #ifndef lint
     static char vcid[] = "string";
     #endif /* lint */

Note that the text above starts with a blank line.

If you use more than one version header in a file, put them close together in the file. The mechanism in revert-buffer that preserves markers may not handle markers positioned between two version headers.

Previous: Miscellaneous VC, Up: Version Control

23.7.10 Customizing VC

The variable vc-handled-backends determines which version control systems VC should handle. The default value is (RCS CVS SVN SCCS Arch MCVS), so it contains all six version systems that are currently supported. If you want VC to ignore one or more of these systems, exclude its name from the list. To disable VC entirely, set this variable to nil.

The order of systems in the list is significant: when you visit a file registered in more than one system (see Local Version Control), VC uses the system that comes first in vc-handled-backends by default. The order is also significant when you register a file for the first time, see Registering for details.

Next: , Up: Customizing VC General Options

Emacs normally does not save backup files for source files that are maintained with version control. If you want to make backup files even for files that use version control, set the variable vc-make-backup-files to a non-nil value.

Normally the work file exists all the time, whether it is locked or not. If you set vc-keep-workfiles to nil, then checking in a new version with C-x v v deletes the work file; but any attempt to visit the file with Emacs creates it again. (With CVS, work files are always kept.)

Editing a version-controlled file through a symbolic link can be dangerous. It bypasses the version control system—you can edit the file without locking it, and fail to check your changes in. Also, your changes might overwrite those of another user. To protect against this, VC checks each symbolic link that you visit, to see if it points to a file under version control.

The variable vc-follow-symlinks controls what to do when a symbolic link points to a version-controlled file. If it is nil, VC only displays a warning message. If it is t, VC automatically follows the link, and visits the real file instead, telling you about this in the echo area. If the value is ask (the default), VC asks you each time whether to follow the link.

If vc-suppress-confirm is non-nil, then C-x v v and C-x v i can save the current buffer without asking, and C-x v u also operates without asking for confirmation. (This variable does not affect C-x v c; that operation is so drastic that it should always ask for confirmation.)

VC mode does much of its work by running the shell commands for RCS, CVS and SCCS. If vc-command-messages is non-nil, VC displays messages to indicate which shell commands it runs, and additional messages when the commands finish.

You can specify additional directories to search for version control programs by setting the variable vc-path. These directories are searched before the usual search path. It is rarely necessary to set this variable, because VC normally finds the proper files automatically.

Next: , Previous: General VC Options, Up: Customizing VC Options for RCS and SCCS

By default, RCS uses locking to coordinate the activities of several users, but there is a mode called non-strict locking in which you can check-in changes without locking the file first. Use ‘rcs -U’ to switch to non-strict locking for a particular file, see the rcs manual page for details.

When deducing the version control state of an RCS file, VC first looks for an RCS version header string in the file (see Version Headers). If there is no header string, VC normally looks at the file permissions of the work file; this is fast. But there might be situations when the file permissions cannot be trusted. In this case the master file has to be consulted, which is rather expensive. Also the master file can only tell you if there's any lock on the file, but not whether your work file really contains that locked version.

You can tell VC not to use version headers to determine the file status by setting vc-consult-headers to nil. VC then always uses the file permissions (if it is supposed to trust them), or else checks the master file.

You can specify the criterion for whether to trust the file permissions by setting the variable vc-mistrust-permissions. Its value can be t (always mistrust the file permissions and check the master file), nil (always trust the file permissions), or a function of one argument which makes the decision. The argument is the directory name of the RCS subdirectory. A non-nil value from the function says to mistrust the file permissions. If you find that the file permissions of work files are changed erroneously, set vc-mistrust-permissions to t. Then VC always checks the master file to determine the file's status.

VC determines the version control state of files under SCCS much as with RCS. It does not consider SCCS version headers, though. Thus, the variable vc-mistrust-permissions affects SCCS use, but vc-consult-headers does not.

Previous: RCS and SCCS, Up: Customizing VC Options specific for CVS

By default, CVS does not use locking to coordinate the activities of several users; anyone can change a work file at any time. However, there are ways to restrict this, resulting in behavior that resembles locking.

For one thing, you can set the CVSREAD environment variable (the value you use makes no difference). If this variable is defined, CVS makes your work files read-only by default. In Emacs, you must type C-x v v to make the file writable, so that editing works in fact similar as if locking was used. Note however, that no actual locking is performed, so several users can make their files writable at the same time. When setting CVSREAD for the first time, make sure to check out all your modules anew, so that the file protections are set correctly.

Another way to achieve something similar to locking is to use the watch feature of CVS. If a file is being watched, CVS makes it read-only by default, and you must also use C-x v v in Emacs to make it writable. VC calls cvs edit to make the file writable, and CVS takes care to notify other developers of the fact that you intend to change the file. See the CVS documentation for details on using the watch feature.

When a file's repository is on a remote machine, VC tries to keep network interactions to a minimum. This is controlled by the variable vc-cvs-stay-local. If it is t (the default), then VC uses only the entry in the local CVS subdirectory to determine the file's state (and possibly information returned by previous CVS commands). One consequence of this is that when you have modified a file, and somebody else has already checked in other changes to the file, you are not notified of it until you actually try to commit. (But you can try to pick up any recent changes from the repository first, using C-x v m <RET>, see Merging).

The variable vc-cvs-global-switches, if non-nil, should be a string specifying switches to pass to CVS for all CVS operations.

When vc-cvs-stay-local is t, VC also makes local version backups, so that simple diff and revert operations are completely local (see Version Backups).

On the other hand, if you set vc-cvs-stay-local to nil, then VC queries the remote repository before it decides what to do in vc-next-action (C-x v v), just as it does for local repositories. It also does not make any version backups.

You can also set vc-cvs-stay-local to a regular expression that is matched against the repository host name; VC then stays local only for repositories from hosts that match the pattern.

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23.8 File Directories

The file system groups files into directories. A directory listing is a list of all the files in a directory. Emacs provides commands to create and delete directories, and to make directory listings in brief format (file names only) and verbose format (sizes, dates, and authors included). There is also a directory browser called Dired; see Dired.

C-x C-d dir-or-pattern <RET>
Display a brief directory listing (list-directory).
C-u C-x C-d dir-or-pattern <RET>
Display a verbose directory listing.
M-x make-directory <RET> dirname <RET>
Create a new directory named dirname.
M-x delete-directory <RET> dirname <RET>
Delete the directory named dirname. It must be empty, or you get an error.

The command to display a directory listing is C-x C-d (list-directory). It reads using the minibuffer a file name which is either a directory to be listed or a wildcard-containing pattern for the files to be listed. For example,

     C-x C-d /u2/emacs/etc <RET>

lists all the files in directory /u2/emacs/etc. Here is an example of specifying a file name pattern:

     C-x C-d /u2/emacs/src/*.c <RET>

Normally, C-x C-d displays a brief directory listing containing just file names. A numeric argument (regardless of value) tells it to make a verbose listing including sizes, dates, and owners (like ‘ls -l’).

The text of a directory listing is mostly obtained by running ls in an inferior process. Two Emacs variables control the switches passed to ls: list-directory-brief-switches is a string giving the switches to use in brief listings ("-CF" by default), and list-directory-verbose-switches is a string giving the switches to use in a verbose listing ("-l" by default).

Emacs adds information about the amount of free space on the disk that contains the directory. To do this, it runs the program specified by directory-free-space-program with arguments directory-free-space-args.

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23.9 Comparing Files

The command M-x diff compares two files, displaying the differences in an Emacs buffer named ‘*diff*’. It works by running the diff program, using options taken from the variable diff-switches. The value of diff-switches should be a string; the default is "-c" to specify a context diff.

After running M-x diff, you can use C-x ` to visit successive changed locations in the two source files, as in Compilation mode (see Compilation Mode.) In the ‘*diff*’ buffer, you can move to a particular hunk of changes and type C-c C-c (diff-goto-source) to visit the corresponding source location.

The command M-x diff-backup compares a specified file with its most recent backup. If you specify the name of a backup file, diff-backup compares it with the source file that it is a backup of.

The command M-x compare-windows compares the text in the current window with that in the next window. (For more information about windows in Emacs, Windows.) Comparison starts at point in each window, after pushing each initial point value on the mark ring in its respective buffer. Then it moves point forward in each window, one character at a time, until it reaches characters that don't match. Then the command exits.

If point in the two windows is followed by non-matching text when the command starts, it tries heuristically to advance up to matching text in the two windows, and then exits. So if you use M-x compare-windows repeatedly, each time it either skips one matching range or finds the start of another.

With a numeric argument, compare-windows ignores changes in whitespace. If the variable compare-ignore-case is non-nil, the comparison ignores differences in case as well. If the variable compare-ignore-whitespace is non-nil, compare-windows normally ignores changes in whitespace, and a prefix argument turns that off.

Differences between versions of files are often distributed as patches, which are the output from diff or a version control system that uses diff. M-x diff-mode turns on Diff mode, a major mode for viewing and editing patches, either as “unified diffs” or “context diffs.”

You can use M-x smerge-mode to turn on Smerge mode, a minor mode for editing output from the diff3 program. This is typically the result of a failed merge from a version control system “update” outside VC, due to conflicting changes to a file. Smerge mode provides commands to resolve conflicts by selecting specific changes.

See also Emerge, and Top, for convenient facilities for merging two similar files.

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23.10 Miscellaneous File Operations

Emacs has commands for performing many other operations on files. All operate on one file; they do not accept wildcard file names.

M-x view-file allows you to scan or read a file by sequential screenfuls. It reads a file name argument using the minibuffer. After reading the file into an Emacs buffer, view-file displays the beginning. You can then type <SPC> to scroll forward one windowful, or <DEL> to scroll backward. Various other commands are provided for moving around in the file, but none for changing it; type ? while viewing for a list of them. They are mostly the same as normal Emacs cursor motion commands. To exit from viewing, type q. The commands for viewing are defined by a special minor mode called View mode.

A related command, M-x view-buffer, views a buffer already present in Emacs. See Misc Buffer.

M-x insert-file (also C-x i) inserts a copy of the contents of the specified file into the current buffer at point, leaving point unchanged before the contents and the mark after them.

M-x write-region is the inverse of M-x insert-file; it copies the contents of the region into the specified file. M-x append-to-file adds the text of the region to the end of the specified file. See Accumulating Text. The variable write-region-inhibit-fsync applies to these commands, as well as saving files; see Customize Save.

M-x delete-file deletes the specified file, like the rm command in the shell. If you are deleting many files in one directory, it may be more convenient to use Dired (see Dired).

M-x rename-file reads two file names old and new using the minibuffer, then renames file old as new. If the file name new already exists, you must confirm with yes or renaming is not done; this is because renaming causes the old meaning of the name new to be lost. If old and new are on different file systems, the file old is copied and deleted.

If the argument new is just a directory name, the real new name is in that directory, with the same non-directory component as old. For example, M-x rename-file RET ~/foo RET /tmp RET renames ~/foo to /tmp/foo. The same rule applies to all the remaining commands in this section. All of them ask for confirmation when the new file name already exists, too.

The similar command M-x add-name-to-file is used to add an additional name to an existing file without removing its old name. The new name is created as a “hard link” to the existing file. The new name must belong on the same file system that the file is on. On MS-Windows, this command works only if the file resides in an NTFS file system. On MS-DOS, it works by copying the file.

M-x copy-file reads the file old and writes a new file named new with the same contents.

M-x make-symbolic-link reads two file names target and linkname, then creates a symbolic link named linkname, which points at target. The effect is that future attempts to open file linkname will refer to whatever file is named target at the time the opening is done, or will get an error if the name target is nonexistent at that time. This command does not expand the argument target, so that it allows you to specify a relative name as the target of the link.

Not all systems support symbolic links; on systems that don't support them, this command is not defined.

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23.11 Accessing Compressed Files

Emacs automatically uncompresses compressed files when you visit them, and automatically recompresses them if you alter them and save them. Emacs recognizes compressed files by their file names. File names ending in ‘.gz’ indicate a file compressed with gzip. Other endings indicate other compression programs.

Automatic uncompression and compression apply to all the operations in which Emacs uses the contents of a file. This includes visiting it, saving it, inserting its contents into a buffer, loading it, and byte compiling it.

To disable this feature, type the command M-x auto-compression-mode. You can disenable it permanently by customizing the variable auto-compression-mode.

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23.12 File Archives

A file whose name ends in ‘.tar’ is normally an archive made by the tar program. Emacs views these files in a special mode called Tar mode which provides a Dired-like list of the contents (see Dired). You can move around through the list just as you would in Dired, and visit the subfiles contained in the archive. However, not all Dired commands are available in Tar mode.

If you enable Auto Compression mode (see Compressed Files), then Tar mode is used also for compressed archives—files with extensions ‘.tgz’, .tar.Z and .tar.gz.

The keys e, f and <RET> all extract a component file into its own buffer. You can edit it there and when you save the buffer the edited version will replace the version in the Tar buffer. v extracts a file into a buffer in View mode. o extracts the file and displays it in another window, so you could edit the file and operate on the archive simultaneously. d marks a file for deletion when you later use x, and u unmarks a file, as in Dired. C copies a file from the archive to disk and R renames a file. g reverts the buffer from the archive on disk.

The keys M, G, and O change the file's permission bits, group, and owner, respectively.

If your display supports colors and the mouse, moving the mouse pointer across a file name highlights that file name, indicating that you can click on it. Clicking Mouse-2 on the highlighted file name extracts the file into a buffer and displays that buffer.

Saving the Tar buffer writes a new version of the archive to disk with the changes you made to the components.

You don't need the tar program to use Tar mode—Emacs reads the archives directly. However, accessing compressed archives requires the appropriate uncompression program.

A separate but similar Archive mode is used for archives produced by the programs arc, jar, lzh, zip, and zoo, which have extensions corresponding to the program names.

The key bindings of Archive mode are similar to those in Tar mode, with the addition of the m key which marks a file for subsequent operations, and M-<DEL> which unmarks all the marked files. Also, the a key toggles the display of detailed file information, for those archive types where it won't fit in a single line. Operations such as renaming a subfile, or changing its mode or owner, are supported only for some of the archive formats.

Unlike Tar mode, Archive mode runs the archiving program to unpack and repack archives. Details of the program names and their options can be set in the ‘Archive’ Customize group. However, you don't need these programs to look at the archive table of contents, only to extract or manipulate the subfiles in the archive.

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23.13 Remote Files

You can refer to files on other machines using a special file name syntax:


To carry out this request, Emacs uses either the FTP program or a remote-login program such as ssh, rlogin, or telnet. You can always specify in the file name which method to use—for example, /ftp:user@host:filename uses FTP, whereas /ssh:user@host:filename uses ssh. When you don't specify a method in the file name, Emacs chooses the method as follows:

  1. If the host name starts with ‘ftp.’ (with dot), then Emacs uses FTP.
  2. If the user name is ‘ftp’ or ‘anonymous’, then Emacs uses FTP.
  3. Otherwise, Emacs uses ssh.

Remote file access through FTP is handled by the Ange-FTP package, which is documented in the following. Remote file access through the other methods is handled by the Tramp package, which has its own manual. See The Tramp Manual.

When the Ange-FTP package is used, Emacs logs in through FTP using your user name or the name user. It may ask you for a password from time to time; this is used for logging in on host. The form using port allows you to access servers running on a non-default TCP port.

If you want to disable backups for remote files, set the variable ange-ftp-make-backup-files to nil.

By default, the auto-save files (see Auto Save Files) for remote files are made in the temporary file directory on the local machine. This is achieved using the variable auto-save-file-name-transforms.

Normally, if you do not specify a user name in a remote file name, that means to use your own user name. But if you set the variable ange-ftp-default-user to a string, that string is used instead. (The Emacs package that implements FTP file access is called ange-ftp.)

To visit files accessible by anonymous FTP, you use special user names ‘anonymous’ or ‘ftp’. Passwords for these user names are handled specially. The variable ange-ftp-generate-anonymous-password controls what happens: if the value of this variable is a string, then that string is used as the password; if non-nil (the default), then the value of user-mail-address is used; if nil, the user is prompted for a password as normal.

Sometimes you may be unable to access files on a remote machine because a firewall in between blocks the connection for security reasons. If you can log in on a gateway machine from which the target files are accessible, and whose FTP server supports gatewaying features, you can still use remote file names; all you have to do is specify the name of the gateway machine by setting the variable ange-ftp-gateway-host, and set ange-ftp-smart-gateway to t. Otherwise you may be able to make remote file names work, but the procedure is complex. You can read the instructions by typing M-x finder-commentary <RET> ange-ftp <RET>.

You can entirely turn off the FTP file name feature by removing the entries ange-ftp-completion-hook-function and ange-ftp-hook-function from the variable file-name-handler-alist. You can turn off the feature in individual cases by quoting the file name with ‘/:’ (see Quoted File Names).

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23.14 Quoted File Names

You can quote an absolute file name to prevent special characters and syntax in it from having their special effects. The way to do this is to add ‘/:’ at the beginning.

For example, you can quote a local file name which appears remote, to prevent it from being treated as a remote file name. Thus, if you have a directory named /foo: and a file named bar in it, you can refer to that file in Emacs as ‘/:/foo:/bar’.

/:’ can also prevent ‘~’ from being treated as a special character for a user's home directory. For example, /:/tmp/~hack refers to a file whose name is ~hack in directory /tmp.

Quoting with ‘/:’ is also a way to enter in the minibuffer a file name that contains ‘$’. In order for this to work, the ‘/:’ must be at the beginning of the minibuffer contents. (You can also double each ‘$’; see File Names with $.)

You can also quote wildcard characters with ‘/:’, for visiting. For example, /:/tmp/foo*bar visits the file /tmp/foo*bar.

Another method of getting the same result is to enter /tmp/foo[*]bar, which is a wildcard specification that matches only /tmp/foo*bar. However, in many cases there is no need to quote the wildcard characters because even unquoted they give the right result. For example, if the only file name in /tmp that starts with ‘foo’ and ends with ‘bar’ is foo*bar, then specifying /tmp/foo*bar will visit only /tmp/foo*bar.

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23.15 File Name Cache

You can use the file name cache to make it easy to locate a file by name, without having to remember exactly where it is located. When typing a file name in the minibuffer, C-<tab> (file-cache-minibuffer-complete) completes it using the file name cache. If you repeat C-<tab>, that cycles through the possible completions of what you had originally typed. Note that the C-<tab> character cannot be typed on most text-only terminals.

The file name cache does not fill up automatically. Instead, you load file names into the cache using these commands:

M-x file-cache-add-directory <RET> directory <RET>
Add each file name in directory to the file name cache.
M-x file-cache-add-directory-using-find <RET> directory <RET>
Add each file name in directory and all of its nested subdirectories to the file name cache.
M-x file-cache-add-directory-using-locate <RET> directory <RET>
Add each file name in directory and all of its nested subdirectories to the file name cache, using locate to find them all.
M-x file-cache-add-directory-list <RET> variable <RET>
Add each file name in each directory listed in variable to the file name cache. variable should be a Lisp variable such as load-path or exec-path, whose value is a list of directory names.
M-x file-cache-clear-cache <RET>
Clear the cache; that is, remove all file names from it.

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23.16 Convenience Features for Finding Files

In this section, we introduce some convenient facilities for finding recently-opened files, reading file names from a buffer, and viewing image files.

If you enable Recentf mode, with M-x recentf-mode, the ‘File’ menu includes a submenu containing a list of recently opened files. M-x recentf-save-list saves the current recent-file-list to a file, and M-x recentf-edit-list edits it.

The M-x ffap command generalizes find-file with more powerful heuristic defaults (see FFAP), often based on the text at point. Partial Completion mode offers other features extending find-file, which can be used with ffap. See Completion Options.

Visiting image files automatically selects Image mode. This major mode allows you to toggle between displaying the file as an image in the Emacs buffer, and displaying its underlying text representation, using the command C-c C-c (image-toggle-display). This works only when Emacs can display the specific image type.

Thumbs mode is a major mode for viewing directories containing many image files. To use it, type M-x thumbs and specify the directory to view. The images in that directory will be displayed in a ‘Thumbs’ buffer as thumbnails; type RET on a thumbnail to view the full-size image. Thumbs mode requires the convert program, which is part of the ImageMagick software package.

Previous: File Conveniences, Up: Files

23.17 Filesets

If you regularly edit a certain group of files, you can define them as a fileset. This lets you perform certain operations, such as visiting, query-replace, and shell commands on all the files at once. To make use of filesets, you must first add the expression (filesets-init) to your .emacs file (see Init File). This adds a ‘Filesets’ menu to the menu bar.

The simplest way to define filesets is by adding files to them one at a time. To add a file to fileset name, visit the file and type M-x filesets-add-buffer RET name RET. If there is no fileset name, this creates a new one, which initially creates only the current file. The command M-x filesets-remove-buffer removes the current file from a fileset.

You can also edit the list of filesets directly, with M-x filesets-edit (or by choosing ‘Edit Filesets’ from the ‘Filesets’ menu). The editing is performed in a Customize buffer (see Easy Customization). Filesets need not be a simple list of files—you can also define filesets using regular expression matching file names. Some examples of these more complicated filesets are shown in the Customize buffer. Remember to select ‘Save for future sessions’ if you want to use the same filesets in future Emacs sessions.

You can use the command M-x filesets-open to visit all the files in a fileset, and M-x filesets-close to close them. Use M-x filesets-run-cmd to run a shell command on all the files in a fileset. These commands are also available from the ‘Filesets’ menu, where each existing fileset is represented by a submenu.

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24 Using Multiple Buffers

The text you are editing in Emacs resides in an object called a buffer. Each time you visit a file, a buffer is created to hold the file's text. Each time you invoke Dired, a buffer is created to hold the directory listing. If you send a message with C-x m, a buffer named ‘*mail*’ is used to hold the text of the message. When you ask for a command's documentation, that appears in a buffer called ‘*Help*’.

At any time, one and only one buffer is current. It is also called the selected buffer. Often we say that a command operates on “the buffer” as if there were only one; but really this means that the command operates on the current buffer (most commands do).

When Emacs has multiple windows, each window has its own chosen buffer and displays it; at any time, only one of the windows is selected, and its chosen buffer is the current buffer. Each window's mode line normally displays the name of the window's chosen buffer (see Windows).

Each buffer has a name, which can be of any length, and you can select any buffer by giving its name. Most buffers are made by visiting files, and their names are derived from the files' names. But you can also create an empty buffer with any name you want. A newly started Emacs has a buffer named ‘*scratch*’ which can be used for evaluating Lisp expressions in Emacs. The distinction between upper and lower case matters in buffer names.

Each buffer records individually what file it is visiting, whether it is modified, and what major mode and minor modes are in effect in it (see Major Modes). Any Emacs variable can be made local to a particular buffer, meaning its value in that buffer can be different from the value in other buffers. See Locals.

A buffer's size cannot be larger than some maximum, which is defined by the largest buffer position representable by the Emacs integer data type. This is because Emacs tracks buffer positions using that data type. For 32-bit machines, the largest buffer size is 256 megabytes.

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24.1 Creating and Selecting Buffers

C-x b buffer <RET>
Select or create a buffer named buffer (switch-to-buffer).
C-x 4 b buffer <RET>
Similar, but select buffer in another window (switch-to-buffer-other-window).
C-x 5 b buffer <RET>
Similar, but select buffer in a separate frame (switch-to-buffer-other-frame).
C-x <LEFT>
Select the previous buffer in the list of existing buffers.
Select the next buffer in the list of existing buffers.
C-u M-g M-g
C-u M-g g
Read a number n and move to line n in the most recently selected buffer other than the current buffer.

To select the buffer named bufname, type C-x b bufname <RET>. This runs the command switch-to-buffer with argument bufname. You can use completion on an abbreviation for the buffer name you want (see Completion). An empty argument to C-x b specifies the buffer that was current most recently among those not now displayed in any window.

For conveniently switching between a few buffers, use the commands C-x <LEFT> and C-x <RIGHT>. C-x <RIGHT> (previous-buffer) selects the previous buffer (following the order of most recent selection in the current frame), while C-x <LEFT> (next-buffer) moves through buffers in the reverse direction.

To select a buffer in a window other than the current one, type C-x 4 b bufname <RET>. This runs the command switch-to-buffer-other-window which displays the buffer bufname in another window. By default, if displaying the buffer causes two vertically adjacent windows to be displayed, the heights of those windows are evened out; to countermand that and preserve the window configuration, set the variable even-window-heights to nil.

Similarly, C-x 5 b buffer <RET> runs the command switch-to-buffer-other-frame which selects a buffer in another frame.

You can control how certain buffers are handled by these commands by customizing the variables special-display-buffer-names, special-display-regexps, same-window-buffer-names, and same-window-regexps. See Force Same Window, and Special Buffer Frames, for more about these variables. In addition, if the value of display-buffer-reuse-frames is non-nil, and the buffer you want to switch to is already displayed in some frame, Emacs will raise that frame.

Most buffers are created by visiting files, or by Emacs commands that want to display some text, but you can also create a buffer explicitly by typing C-x b bufname <RET>. This makes a new, empty buffer that is not visiting any file, and selects it for editing. Such buffers are used for making notes to yourself. If you try to save one, you are asked for the file name to use. The new buffer's major mode is determined by the value of default-major-mode (see Major Modes).

Note that C-x C-f, and any other command for visiting a file, can also be used to switch to an existing file-visiting buffer. See Visiting.

C-u M-g M-g, that is goto-line with a prefix argument of just C-u, reads a number n using the minibuffer, selects the most recently selected buffer other than the current buffer in another window, and then moves point to the beginning of line number n in that buffer. This is mainly useful in a buffer that refers to line numbers in another buffer: if point is on or just after a number, goto-line uses that number as the default for n. Note that prefix arguments other than just C-u behave differently. C-u 4 M-g M-g goes to line 4 in the current buffer, without reading a number from the minibuffer. (Remember that M-g M-g without prefix argument reads a number n and then moves to line number n in the current buffer.)

Emacs uses buffer names that start with a space for internal purposes. It treats these buffers specially in minor ways—for example, by default they do not record undo information. It is best to avoid using such buffer names yourself.

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24.2 Listing Existing Buffers

C-x C-b
List the existing buffers (list-buffers).

To display a list of existing buffers, type C-x C-b. Each line in the list shows one buffer's name, major mode and visited file. The buffers are listed in the order that they were current; the buffers that were current most recently come first.

*’ in the first field of a line indicates the buffer is “modified.” If several buffers are modified, it may be time to save some with C-x s (see Save Commands). ‘%’ indicates a read-only buffer. ‘.’ marks the current buffer. Here is an example of a buffer list:

     CRM Buffer                Size  Mode              File
     . * .emacs                3294  Emacs-Lisp        ~/.emacs
      %  *Help*                 101  Help
         search.c             86055  C                 ~/cvs/emacs/src/search.c
      %  src                  20959  Dired by name     ~/cvs/emacs/src/
       * *mail*                  42  Mail
      %  HELLO                 1607  Fundamental       ~/cvs/emacs/etc/HELLO
      %  NEWS                481184  Outline           ~/cvs/emacs/etc/NEWS
         *scratch*              191  Lisp Interaction
       * *Messages*            1554  Fundamental

Note that the buffer ‘*Help*’ was made by a help request; it is not visiting any file. The buffer src was made by Dired on the directory ~/cvs/emacs/src/. You can list only buffers that are visiting files by giving the command a prefix; for instance, by typing C-u C-x C-b.

list-buffers omits buffers whose names begin with a space, unless they visit files: such buffers are used internally by Emacs.

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24.3 Miscellaneous Buffer Operations

C-x C-q
Toggle read-only status of buffer (toggle-read-only).
M-x rename-buffer <RET> name <RET>
Change the name of the current buffer.
M-x rename-uniquely
Rename the current buffer by adding ‘<number>’ to the end.
M-x view-buffer <RET> buffer <RET>
Scroll through buffer buffer.

A buffer can be read-only, which means that commands to change its contents are not allowed. The mode line indicates read-only buffers with ‘%%’ or ‘%*’ near the left margin. Read-only buffers are usually made by subsystems such as Dired and Rmail that have special commands to operate on the text; also by visiting a file whose access control says you cannot write it.

If you wish to make changes in a read-only buffer, use the command C-x C-q (toggle-read-only). It makes a read-only buffer writable, and makes a writable buffer read-only. This works by setting the variable buffer-read-only, which has a local value in each buffer and makes the buffer read-only if its value is non-nil. If you have files under version control, you may find it convenient to bind C-x C-q to vc-toggle-read-only instead. Then, typing C-x C-q not only changes the read-only flag, but it also checks the file in or out. See Version Control.

M-x rename-buffer changes the name of the current buffer. Specify the new name as a minibuffer argument. There is no default. If you specify a name that is in use for some other buffer, an error happens and no renaming is done.

M-x rename-uniquely renames the current buffer to a similar name with a numeric suffix added to make it both different and unique. This command does not need an argument. It is useful for creating multiple shell buffers: if you rename the ‘*shell*’ buffer, then do M-x shell again, it makes a new shell buffer named ‘*shell*’; meanwhile, the old shell buffer continues to exist under its new name. This method is also good for mail buffers, compilation buffers, and most Emacs features that create special buffers with particular names. (With some of these features, such as M-x compile, M-x grep an M-x info, you need to switch to some other buffer before using the command, in order for it to make a different buffer.)

M-x view-buffer is much like M-x view-file (see Misc File Ops) except that it examines an already existing Emacs buffer. View mode provides commands for scrolling through the buffer conveniently but not for changing it. When you exit View mode with q, that switches back to the buffer (and the position) which was previously displayed in the window. Alternatively, if you exit View mode with e, the buffer and the value of point that resulted from your perusal remain in effect.

The commands M-x append-to-buffer and M-x insert-buffer can be used to copy text from one buffer to another. See Accumulating Text.

Next: , Previous: Misc Buffer, Up: Buffers

24.4 Killing Buffers

If you continue an Emacs session for a while, you may accumulate a large number of buffers. You may then find it convenient to kill the buffers you no longer need. On most operating systems, killing a buffer releases its space back to the operating system so that other programs can use it. Here are some commands for killing buffers:

C-x k bufname <RET>
Kill buffer bufname (kill-buffer).
M-x kill-some-buffers
Offer to kill each buffer, one by one.

C-x k (kill-buffer) kills one buffer, whose name you specify in the minibuffer. The default, used if you type just <RET> in the minibuffer, is to kill the current buffer. If you kill the current buffer, another buffer becomes current: one that was current in the recent past but is not displayed in any window now. If you ask to kill a file-visiting buffer that is modified (has unsaved editing), then you must confirm with yes before the buffer is killed.

The command M-x kill-some-buffers asks about each buffer, one by one. An answer of y means to kill the buffer. Killing the current buffer or a buffer containing unsaved changes selects a new buffer or asks for confirmation just like kill-buffer.

The buffer menu feature (see Several Buffers) is also convenient for killing various buffers.

If you want to do something special every time a buffer is killed, you can add hook functions to the hook kill-buffer-hook (see Hooks).

If you run one Emacs session for a period of days, as many people do, it can fill up with buffers that you used several days ago. The command M-x clean-buffer-list is a convenient way to purge them; it kills all the unmodified buffers that you have not used for a long time. An ordinary buffer is killed if it has not been displayed for three days; however, you can specify certain buffers that should never be killed automatically, and others that should be killed if they have been unused for a mere hour.

You can also have this buffer purging done for you, every day at midnight, by enabling Midnight mode. Midnight mode operates each day at midnight; at that time, it runs clean-buffer-list, or whichever functions you have placed in the normal hook midnight-hook (see Hooks).

To enable Midnight mode, use the Customization buffer to set the variable midnight-mode to t. See Easy Customization.

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24.5 Operating on Several Buffers

The buffer-menu facility is like a “Dired for buffers”; it allows you to request operations on various Emacs buffers by editing an Emacs buffer containing a list of them. You can save buffers, kill them (here called deleting them, for consistency with Dired), or display them.

M-x buffer-menu
Begin editing a buffer listing all Emacs buffers.
M-x buffer-menu-other-window.
Similar, but do it in another window.

The command buffer-menu writes a list of all Emacs buffers2 into the buffer ‘*Buffer List*’, and selects that buffer in Buffer Menu mode.

The buffer is read-only, and can be changed only through the special commands described in this section. The usual Emacs cursor motion commands can be used in the ‘*Buffer List*’ buffer. The following commands apply to the buffer described on the current line.

Request to delete (kill) the buffer, then move down. The request shows as a ‘D’ on the line, before the buffer name. Requested deletions take place when you type the x command.
Like d but move up afterwards instead of down.
Request to save the buffer. The request shows as an ‘S’ on the line. Requested saves take place when you type the x command. You may request both saving and deletion for the same buffer.
Perform previously requested deletions and saves.
Remove any request made for the current line, and move down.
Move to previous line and remove any request made for that line.

The d, C-d, s and u commands to add or remove flags also move down (or up) one line. They accept a numeric argument as a repeat count.

These commands operate immediately on the buffer listed on the current line:

Mark the buffer “unmodified.” The command ~ does this immediately when you type it.
Toggle the buffer's read-only flag. The command % does this immediately when you type it.
Visit the buffer as a tags table. See Select Tags Table.

There are also commands to select another buffer or buffers:

Quit the buffer menu—immediately display the most recent formerly visible buffer in its place.
Immediately select this line's buffer in place of the ‘*Buffer List*’ buffer.
Immediately select this line's buffer in another window as if by C-x 4 b, leaving ‘*Buffer List*’ visible.
Immediately display this line's buffer in another window, but don't select the window.
Immediately select this line's buffer in a full-screen window.
Immediately set up two windows, with this line's buffer selected in one, and the previously current buffer (aside from the buffer ‘*Buffer List*’) displayed in the other.
Bury the buffer listed on this line.
Mark this line's buffer to be displayed in another window if you exit with the v command. The request shows as a ‘>’ at the beginning of the line. (A single buffer may not have both a delete request and a display request.)
Immediately select this line's buffer, and also display in other windows any buffers previously marked with the m command. If you have not marked any buffers, this command is equivalent to 1.

There is also a command that affects the entire buffer list:

Delete, or reinsert, lines for non-file buffers. This command toggles the inclusion of such buffers in the buffer list.

What buffer-menu actually does is create and switch to a suitable buffer, and turn on Buffer Menu mode in it. Everything else described above is implemented by the special commands provided in Buffer Menu mode. One consequence of this is that you can switch from the ‘*Buffer List*’ buffer to another Emacs buffer, and edit there. You can reselect the ‘*Buffer List*’ buffer later, to perform the operations already requested, or you can kill it, or pay no further attention to it.

The list in the ‘*Buffer List*’ buffer looks exactly like the buffer list described in List Buffers, because they really are the same. The only difference between buffer-menu and list-buffers is that buffer-menu switches to the ‘*Buffer List*’ buffer in the selected window; list-buffers displays the same buffer in another window. If you run list-buffers (that is, type C-x C-b) and select the buffer list manually, you can use all of the commands described here.

Normally, the buffer ‘*Buffer List*’ is not updated automatically when buffers are created and killed; its contents are just text. If you have created, deleted or renamed buffers, the way to update ‘*Buffer List*’ to show what you have done is to type g (revert-buffer) or repeat the buffer-menu command.

The ‘*Buffer List*’ buffer does automatically update every auto-revert-interval seconds if you enable Auto Revert mode in it. (As long as it is not marked modified.) Global Auto Revert mode does not update the ‘*Buffer List*’ buffer by default, but it does if global-auto-revert-non-file-buffers is non-nil. see Autorevert, for details.

The command buffer-menu-other-window works the same as buffer-menu, except that it displays the buffers list in another window.

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24.6 Indirect Buffers

An indirect buffer shares the text of some other buffer, which is called the base buffer of the indirect buffer. In some ways it is the analogue, for buffers, of a symbolic link between files.

M-x make-indirect-buffer <RET> base-buffer <RET> indirect-name <RET>
Create an indirect buffer named indirect-name whose base buffer is base-buffer.
M-x clone-indirect-buffer <RET>
Create an indirect buffer that is a twin copy of the current buffer.
C-x 4 c
Create an indirect buffer that is a twin copy of the current buffer, and select it in another window (clone-indirect-buffer-other-window).

The text of the indirect buffer is always identical to the text of its base buffer; changes made by editing either one are visible immediately in the other. But in all other respects, the indirect buffer and its base buffer are completely separate. They have different names, different values of point, different narrowing, different markers, different major modes, and different local variables.

An indirect buffer cannot visit a file, but its base buffer can. If you try to save the indirect buffer, that actually works by saving the base buffer. Killing the base buffer effectively kills the indirect buffer, but killing an indirect buffer has no effect on its base buffer.

One way to use indirect buffers is to display multiple views of an outline. See Outline Views.

A quick and handy way to make an indirect buffer is with the command M-x clone-indirect-buffer. It creates and selects an indirect buffer whose base buffer is the current buffer. With a numeric argument, it prompts for the name of the indirect buffer; otherwise it uses the name of the current buffer, with a ‘<n>’ suffix added. C-x 4 c (clone-indirect-buffer-other-window) works like M-x clone-indirect-buffer, but it selects the new buffer in another window.

The more general way to make an indirect buffer is with the command M-x make-indirect-buffer. It creates an indirect buffer from buffer base-buffer, under the name indirect-name. It prompts for both base-buffer and indirect-name using the minibuffer.

Previous: Indirect Buffers, Up: Buffers

24.7 Convenience Features and Customization of Buffer Handling

This section describes several modes and features that make it more convenient to switch between buffers.

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24.7.1 Making Buffer Names Unique

When several buffers visit identically-named files, Emacs must give the buffers distinct names. The usual method for making buffer names unique adds ‘<2>’, ‘<3>’, etc. to the end of the buffer names (all but one of them).

Other methods work by adding parts of each file's directory to the buffer name. To select one, customize the variable uniquify-buffer-name-style (see Easy Customization).

For instance, the forward naming method puts part of the directory name at the beginning of the buffer name; using this method, buffers visiting /u/mernst/tmp/Makefile and /usr/projects/zaphod/Makefile would be named ‘tmp/Makefile’ and ‘zaphod/Makefile’, respectively (instead of ‘Makefile’ and ‘Makefile<2>’).

By contrast, the post-forward naming method would call the buffers ‘Makefile|tmp’ and ‘Makefile|zaphod’, and the reverse naming method would call them ‘Makefile\tmp’ and ‘Makefile\zaphod’. The nontrivial difference between post-forward and reverse occurs when just one directory name is not enough to distinguish two files; then reverse puts the directory names in reverse order, so that /top/middle/file becomes ‘file\middle\top’, while post-forward puts them in forward order after the file name, as in ‘file|top/middle’.

Which rule to follow for putting the directory names in the buffer name is not very important if you are going to look at the buffer names before you type one. But as an experienced user, if you know the rule, you won't have to look. And then you may find that one rule or another is easier for you to remember and utilize fast.

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24.7.2 Switching Between Buffers using Substrings

Iswitchb global minor mode provides convenient switching between buffers using substrings of their names. It replaces the normal definitions of C-x b, C-x 4 b, C-x 5 b, and C-x 4 C-o with alternative commands that are somewhat “smarter.”

When one of these commands prompts you for a buffer name, you can type in just a substring of the name you want to choose. As you enter the substring, Iswitchb mode continuously displays a list of buffers that match the substring you have typed.

At any time, you can type <RET> to select the first buffer in the list. So the way to select a particular buffer is to make it the first in the list. There are two ways to do this. You can type more of the buffer name and thus narrow down the list, excluding unwanted buffers above the desired one. Alternatively, you can use C-s and C-r to rotate the list until the desired buffer is first.

<TAB> while entering the buffer name performs completion on the string you have entered, based on the displayed list of buffers.

To enable Iswitchb mode, type M-x iswitchb-mode, or customize the variable iswitchb-mode to t (see Easy Customization).

Previous: Iswitchb, Up: Buffer Convenience

24.7.3 Customizing Buffer Menus

M-x bs-show
Make a list of buffers similarly to M-x list-buffers but customizable.

M-x bs-show pops up a buffer list similar to the one normally displayed by C-x C-b but which you can customize. If you prefer this to the usual buffer list, you can bind this command to C-x C-b. To customize this buffer list, use the bs Custom group (see Easy Customization).

MSB global minor mode (“MSB” stands for “mouse select buffer”) provides a different and customizable mouse buffer menu which you may prefer. It replaces the bindings of mouse-buffer-menu, normally on C-Down-Mouse-1, and the menu bar buffer menu. You can customize the menu in the msb Custom group.

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25 Multiple Windows

Emacs can split a frame into two or many windows. Multiple windows can display parts of different buffers, or different parts of one buffer. Multiple frames always imply multiple windows, because each frame has its own set of windows. Each window belongs to one and only one frame.

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25.1 Concepts of Emacs Windows

Each Emacs window displays one Emacs buffer at any time. A single buffer may appear in more than one window; if it does, any changes in its text are displayed in all the windows where it appears. But the windows showing the same buffer can show different parts of it, because each window has its own value of point.

At any time, one of the windows is the selected window; the buffer this window is displaying is the current buffer. The terminal's cursor shows the location of point in this window. Each other window has a location of point as well. On text-only terminals, there is no way to show where those locations are, since the terminal has only one cursor. If you are using a window system, the location of point in a non-selected window is indicated by a hollow box. The cursor in the selected window is blinking or solid.

Commands to move point affect the value of point for the selected Emacs window only. They do not change the value of point in any other Emacs window, even one showing the same buffer. The same is true for commands such as C-x b to change the current buffer in the selected window; they do not affect other windows at all. However, there are other commands such as C-x 4 b that select a different window and switch buffers in it. Also, all commands that display information in a window, including (for example) C-h f (describe-function) and C-x C-b (list-buffers), work by switching buffers in a nonselected window without affecting the selected window.

When multiple windows show the same buffer, they can have different regions, because they can have different values of point. However, they all have the same value for the mark, because each buffer has only one mark position.

Each window has its own mode line, which displays the buffer name, modification status and major and minor modes of the buffer that is displayed in the window. The selected window's mode line appears in a different color. See Mode Line, for full details on the mode line.

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25.2 Splitting Windows

C-x 2
Split the selected window into two windows, one above the other (split-window-vertically).
C-x 3
Split the selected window into two windows positioned side by side (split-window-horizontally).
In the mode line or scroll bar of a window, split that window.

The command C-x 2 (split-window-vertically) breaks the selected window into two windows, one above the other. Both windows start out displaying the same buffer, with the same value of point. By default the two windows each get half the height of the window that was split; a numeric argument specifies how many lines to give to the top window.

C-x 3 (split-window-horizontally) breaks the selected window into two side-by-side windows. A numeric argument specifies how many columns to give the one on the left. If you are not using scrollbars, a vertical line separates the two windows. You can customize its color with the face vertical-border. Windows that are not the full width of the screen have mode lines, but they are truncated. On terminals where Emacs does not support highlighting, truncated mode lines sometimes do not appear in inverse video.

You can split a window horizontally or vertically by clicking C-Mouse-2 in the mode line or the scroll bar. The line of splitting goes through the place where you click: if you click on the mode line, the new scroll bar goes above the spot; if you click in the scroll bar, the mode line of the split window is side by side with your click.

When a window is less than the full width, text lines too long to fit are frequent. Continuing all those lines might be confusing, so if the variable truncate-partial-width-windows is non-nil, that forces truncation in all windows less than the full width of the screen, independent of the buffer being displayed and its value for truncate-lines. See Display Custom.

Horizontal scrolling is often used in side-by-side windows. See Horizontal Scrolling.

If split-window-keep-point is non-nil, the default, both of the windows resulting from C-x 2 inherit the value of point from the window that was split. This means that scrolling is inevitable. If this variable is nil, then C-x 2 tries to avoid scrolling the text currently visible on the screen, by putting point in each window at a position already visible in the window. It also selects whichever window contains the screen line that the cursor was previously on. Some users prefer the latter mode on slow terminals.

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25.3 Using Other Windows

C-x o
Select another window (other-window). That is o, not zero.
Scroll the next window (scroll-other-window).
M-x compare-windows
Find next place where the text in the selected window does not match the text in the next window.
Mouse-1, in a window's mode line, selects that window but does not move point in it (mouse-select-window).

To select a different window, click with Mouse-1 on its mode line. With the keyboard, you can switch windows by typing C-x o (other-window). That is an o, for “other,” not a zero. When there are more than two windows, this command moves through all the windows in a cyclic order, generally top to bottom and left to right. After the rightmost and bottommost window, it goes back to the one at the upper left corner. A numeric argument means to move several steps in the cyclic order of windows. A negative argument moves around the cycle in the opposite order. When the minibuffer is active, the minibuffer is the last window in the cycle; you can switch from the minibuffer window to one of the other windows, and later switch back and finish supplying the minibuffer argument that is requested. See Minibuffer Edit.

The usual scrolling commands (see Display) apply to the selected window only, but there is one command to scroll the next window. C-M-v (scroll-other-window) scrolls the window that C-x o would select. It takes arguments, positive and negative, like C-v. (In the minibuffer, C-M-v scrolls the window that contains the minibuffer help display, if any, rather than the next window in the standard cyclic order.)

The command M-x compare-windows lets you compare two files or buffers visible in two windows, by moving through them to the next mismatch. See Comparing Files, for details.

If you set mouse-autoselect-window to a non-nil value, moving the mouse into a different window selects that window. This feature is off by default.

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25.4 Displaying in Another Window

C-x 4 is a prefix key for commands that select another window (splitting the window if there is only one) and select a buffer in that window. Different C-x 4 commands have different ways of finding the buffer to select.

C-x 4 b bufname <RET>
Select buffer bufname in another window. This runs switch-to-buffer-other-window.
C-x 4 C-o bufname <RET>
Display buffer bufname in another window, but don't select that buffer or that window. This runs display-buffer.
C-x 4 f filename <RET>
Visit file filename and select its buffer in another window. This runs find-file-other-window. See Visiting.
C-x 4 d directory <RET>
Select a Dired buffer for directory directory in another window. This runs dired-other-window. See Dired.
C-x 4 m
Start composing a mail message in another window. This runs mail-other-window; its same-window analogue is C-x m (see Sending Mail).
C-x 4 .
Find a tag in the current tags table, in another window. This runs find-tag-other-window, the multiple-window variant of M-. (see Tags).
C-x 4 r filename <RET>
Visit file filename read-only, and select its buffer in another window. This runs find-file-read-only-other-window. See Visiting.

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25.5 Forcing Display in the Same Window

Certain Emacs commands switch to a specific buffer with special contents. For example, M-x shell switches to a buffer named ‘*shell*’. By convention, all these commands are written to pop up the buffer in a separate window. But you can specify that certain of these buffers should appear in the selected window.

If you add a buffer name to the list same-window-buffer-names, the effect is that such commands display that particular buffer by switching to it in the selected window. For example, if you add the element "*grep*" to the list, the grep command will display its output buffer in the selected window.

The default value of same-window-buffer-names is not nil: it specifies buffer names ‘*info*’, ‘*mail*’ and ‘*shell*’ (as well as others used by more obscure Emacs packages). This is why M-x shell normally switches to the ‘*shell*’ buffer in the selected window. If you delete this element from the value of same-window-buffer-names, the behavior of M-x shell will change—it will pop up the buffer in another window instead.

You can specify these buffers more generally with the variable same-window-regexps. Set it to a list of regular expressions; then any buffer whose name matches one of those regular expressions is displayed by switching to it in the selected window. (Once again, this applies only to buffers that normally get displayed for you in a separate window.) The default value of this variable specifies Telnet and rlogin buffers.

An analogous feature lets you specify buffers which should be displayed in their own individual frames. See Special Buffer Frames.

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25.6 Deleting and Rearranging Windows

C-x 0
Delete the selected window (delete-window). The last character in this key sequence is a zero.
C-x 1
Delete all windows in the selected frame except the selected window (delete-other-windows).
C-x 4 0
Delete the selected window and kill the buffer that was showing in it (kill-buffer-and-window). The last character in this key sequence is a zero.
C-x ^
Make selected window taller (enlarge-window).
C-x }
Make selected window wider (enlarge-window-horizontally).
C-x {
Make selected window narrower (shrink-window-horizontally).
C-x -
Shrink this window if its buffer doesn't need so many lines (shrink-window-if-larger-than-buffer).
C-x +
Make all windows the same height (balance-windows).
Dragging a window's mode line up or down with Mouse-1 changes window heights.
Mouse-2 in a window's mode line deletes all other windows in the frame (mouse-delete-other-windows).
Mouse-3 in a window's mode line deletes that window (mouse-delete-window), unless the frame has only one window, in which case it buries the current buffer instead and switches to another buffer.

To delete a window, type C-x 0 (delete-window). (That is a zero.) The space occupied by the deleted window is given to an adjacent window (but not the minibuffer window, even if that is active at the time). Once a window is deleted, its attributes are forgotten; only restoring a window configuration can bring it back. Deleting the window has no effect on the buffer it used to display; the buffer continues to exist, and you can select it in any window with C-x b.

C-x 4 0 (kill-buffer-and-window) is a stronger command than C-x 0; it kills the current buffer and then deletes the selected window.

C-x 1 (delete-other-windows) is more powerful in a different way; it deletes all the windows except the selected one (and the minibuffer); the selected window expands to use the whole frame except for the echo area.

You can also delete a window by clicking on its mode line with Mouse-3, and delete all the windows in a frame except one window by clicking on that window's mode line with Mouse-2.

You can also adjust window heights and widths with the mouse. If you press Mouse-1 on a mode line, you can drag that mode line up or down, changing the heights of the windows above and below it. If you press it on the divider between two consecutive mode lines, you can drag that divider right or left, changing the widths of the windows to either side. Note that changing heights and widths with the mouse never deletes windows, it just refuses to make any window smaller than it can be.

To readjust the division of space among vertically adjacent windows, use C-x ^ (enlarge-window). It makes the currently selected window get one line bigger, or as many lines as is specified with a numeric argument. With a negative argument, it makes the selected window smaller. C-x } (enlarge-window-horizontally) makes the selected window wider by the specified number of columns. C-x { (shrink-window-horizontally) makes the selected window narrower by the specified number of columns.

When you make a window bigger, the space comes from one of its neighbors. If this makes any window too small, it is deleted and its space is given to an adjacent window. The minimum size is specified by the variables window-min-height and window-min-width.

The command C-x - (shrink-window-if-larger-than-buffer) reduces the height of the selected window, if it is taller than necessary to show the whole text of the buffer it is displaying. It gives the extra lines to other windows in the frame.

You can also use C-x + (balance-windows) to even out the heights of all the windows in the selected frame.

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25.7 Window Handling Convenience Features and Customization

M-x winner-mode is a global minor mode that records the changes in the window configuration (i.e. how the frames are partitioned into windows), so that you can “undo” them. To undo, use C-c left (winner-undo). If you change your mind while undoing, you can redo the changes you had undone using C-c right (M-x winner-redo). Another way to enable Winner mode is by customizing the variable winner-mode.

The Windmove commands move directionally between neighboring windows in a frame. M-x windmove-right selects the window immediately to the right of the currently selected one, and similarly for the “left,” “up,” and “down” counterparts. M-x windmove-default-keybindings binds these commands to S-right etc. (Not all terminals support shifted arrow keys, however.)

Follow minor mode (M-x follow-mode) synchronizes several windows on the same buffer so that they always display adjacent sections of that buffer. See Follow Mode.

M-x scroll-all-mode provides commands to scroll all visible windows together. You can also turn it on by customizing the variable scroll-all-mode. The commands provided are M-x scroll-all-scroll-down-all, M-x scroll-all-page-down-all and their corresponding “up” equivalents. To make this mode useful, you should bind these commands to appropriate keys.

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26 Frames and X Windows

When using the X Window System, you can create multiple windows at the X level in a single Emacs session. Each X window that belongs to Emacs displays a frame which can contain one or several Emacs windows. A frame initially contains a single general-purpose Emacs window which you can subdivide vertically or horizontally into smaller windows. A frame normally contains its own echo area and minibuffer, but you can make frames that don't have these—they use the echo area and minibuffer of another frame.

Editing you do in one frame also affects the other frames. For instance, if you put text in the kill ring in one frame, you can yank it in another frame. If you exit Emacs through C-x C-c in one frame, it terminates all the frames. To delete just one frame, use C-x 5 0 (that is zero, not o).

To avoid confusion, we reserve the word “window” for the subdivisions that Emacs implements, and never use it to refer to a frame.

Emacs compiled for MS-DOS emulates some aspects of the window system so that you can use many of the features described in this chapter. See MS-DOS Mouse, for more information.

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26.1 Mouse Commands for Editing

The mouse commands for selecting and copying a region are mostly compatible with the xterm program. You can use the same mouse commands for copying between Emacs and other window-based programs. Most of these commands also work in Emacs when you run it under an xterm terminal.

If you select a region with any of these mouse commands, and then immediately afterward type the <DELETE> function key, it deletes the region that you selected. The <BACKSPACE> function key and the ASCII character <DEL> do not do this; if you type any other key in between the mouse command and <DELETE>, it does not do this.

Move point to where you click (mouse-set-point). This is normally the left button.

Normally, Emacs does not distinguish between ordinary mouse clicks and clicks that select a frame. When you click on a frame to select it, that also changes the selected window and cursor position according to the mouse click position. On the X window system, you can change this behavior by setting the variable x-mouse-click-focus-ignore-position to t. Then the first click selects the frame, but does not affect the selected window or cursor position. If you click again in the same place, since that click will be in the selected frame, it will change the window or cursor position.

Set the region to the text you select by dragging, and copy it to the kill ring (mouse-set-region). You can specify both ends of the region with this single command.

If you move the mouse off the top or bottom of the window while dragging, the window scrolls at a steady rate until you move the mouse back into the window. This way, you can select regions that don't fit entirely on the screen. The number of lines scrolled per step depends on how far away from the window edge the mouse has gone; the variable mouse-scroll-min-lines specifies a minimum step size.

If the variable mouse-drag-copy-region is nil, this mouse command does not copy the selected region into the kill ring.

Yank the last killed text, where you click (mouse-yank-at-click). This is normally the middle button.
This command, mouse-save-then-kill, has several functions depending on where you click and the status of the region.

The most basic case is when you click Mouse-1 in one place and then Mouse-3 in another. This selects the text between those two positions as the region. It also copies the new region to the kill ring, so that you can copy it to someplace else.

If you click Mouse-1 in the text, scroll with the scroll bar, and then click Mouse-3, it remembers where point was before scrolling (where you put it with Mouse-1), and uses that position as the other end of the region. This is so that you can select a region that doesn't fit entirely on the screen.

More generally, if you do not have a highlighted region, Mouse-3 selects the text between point and the click position as the region. It does this by setting the mark where point was, and moving point to where you click.

If you have a highlighted region, or if the region was set just before by dragging button 1, Mouse-3 adjusts the nearer end of the region by moving it to where you click. The adjusted region's text also replaces the old region's text in the kill ring.

If you originally specified the region using a double or triple Mouse-1, so that the region is defined to consist of entire words or lines, then adjusting the region with Mouse-3 also proceeds by entire words or lines.

If you use Mouse-3 a second time consecutively, at the same place, that kills the region already selected.

This key sets the region around the word which you click on. If you click on a character with “symbol” syntax (such as underscore, in C mode), it sets the region around the symbol surrounding that character.

If you click on a character with open-parenthesis or close-parenthesis syntax, it sets the region around the parenthetical grouping which that character starts or ends. If you click on a character with string-delimiter syntax (such as a singlequote or doublequote in C), it sets the region around the string constant (using heuristics to figure out whether that character is the beginning or the end of it).

This key selects a region made up of the words you drag across.
This key sets the region around the line you click on.
This key selects a region made up of the lines you drag across.

The simplest way to kill text with the mouse is to press Mouse-1 at one end, then press Mouse-3 twice at the other end. See Killing. To copy the text into the kill ring without deleting it from the buffer, press Mouse-3 just once—or just drag across the text with Mouse-1. Then you can copy it elsewhere by yanking it.

To yank the killed or copied text somewhere else, move the mouse there and press Mouse-2. See Yanking. However, if mouse-yank-at-point is non-nil, Mouse-2 yanks at point. Then it does not matter where you click, or even which of the frame's windows you click on. The default value is nil. This variable also affects yanking the secondary selection.

To copy text to another X window, kill it or save it in the kill ring. Under X, this also sets the primary selection. Then use the “paste” or “yank” command of the program operating the other window to insert the text from the selection.

To copy text from another X window, use the “cut” or “copy” command of the program operating the other window, to select the text you want. Then yank it in Emacs with C-y or Mouse-2.

The standard coding system for X selections is compound-text-with-extensions. To specify another coding system for X selections, use C-x <RET> x or C-x <RET> X. See Specify Coding.

When Emacs puts text into the kill ring, or rotates text to the front of the kill ring, it sets the primary selection in the X server. This is how other X clients can access the text. Emacs also stores the text in the cut buffer, but only if the text is short enough (the value of x-cut-buffer-max specifies the maximum number of characters); putting long strings in the cut buffer can be slow.

The commands to yank the first entry in the kill ring actually check first for a primary selection in another program; after that, they check for text in the cut buffer. If neither of those sources provides text to yank, the kill ring contents are used.

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26.2 Secondary Selection

The secondary selection is another way of selecting text using X. It does not use point or the mark, so you can use it to kill text without setting point or the mark.

Set the secondary selection, with one end at the place where you press down the button, and the other end at the place where you release it (mouse-set-secondary). The highlighting appears and changes as you drag. You can control the appearance of the highlighting by customizing the secondary-selection face (see Face Customization).

If you move the mouse off the top or bottom of the window while dragging, the window scrolls at a steady rate until you move the mouse back into the window. This way, you can mark regions that don't fit entirely on the screen.

This way of setting the secondary selection does not alter the kill ring.

Set one endpoint for the secondary selection (mouse-start-secondary).

Make a secondary selection, using the place specified with M-Mouse-1 as the other end (mouse-secondary-save-then-kill). This also puts the selected text in the kill ring. A second click at the same place kills the secondary selection just made.

Insert the secondary selection where you click (mouse-yank-secondary). This places point at the end of the yanked text.

Double or triple clicking of M-Mouse-1 operates on words and lines, much like Mouse-1.

If mouse-yank-at-point is non-nil, M-Mouse-2 yanks at point. Then it does not matter precisely where you click; all that matters is which window you click on. See Mouse Commands.

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26.3 Using the Clipboard

Apart from the primary and secondary selection types, X supports a clipboard selection type which is used by some applications, particularly under OpenWindows and Gnome.

The command M-x menu-bar-enable-clipboard makes the Cut, Paste and Copy menu items, as well as the keys of the same names, all use the clipboard.

You can customize the variable x-select-enable-clipboard to make the Emacs yank functions consult the clipboard before the primary selection, and to make the kill functions to store in the clipboard as well as the primary selection. Otherwise they do not access the clipboard at all. Using the clipboard is the default on MS-Windows, unlike most systems.

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26.4 Following References with the Mouse

Some read-only Emacs buffers include references you can follow, or commands you can activate. These include names of files, of buffers, of possible completions, of matches for a pattern, as well as the buttons in Help buffers and customization buffers. You can follow the reference or activate the command by moving point to it and typing <RET>. You can also do this with the mouse, using either Mouse-1 or Mouse-2.

Since yanking text into a read-only buffer is not allowed, these buffers generally define Mouse-2 to follow a reference or activate a command. For example, if you click Mouse-2 on a file name in a Dired buffer, you visit that file. If you click Mouse-2 on an error message in the ‘*Compilation*’ buffer, you go to the source code for that error message. If you click Mouse-2 on a completion in the ‘*Completions*’ buffer, you choose that completion.

However, most applications use Mouse-1 to do this sort of thing, so Emacs implements this too. If you click Mouse-1 quickly on a reference or button, it follows or activates. If you click slowly, it moves point as usual. Dragging, meaning moving the mouse while it is held down, also has its usual behavior of setting the region.

Normally, the Mouse-1 click behavior is performed on links in any window. The variable mouse-1-click-in-non-selected-windows controls whether Mouse-1 has this behavior even in non-selected windows, or only in the selected window.

You can usually tell when Mouse-1 and Mouse-2 have this special sort of meaning because the sensitive text highlights when you move the mouse over it. The variable mouse-highlight controls whether to do this highlighting always (even when such text appears where the mouse already is), never, or only immediately after you move the mouse.

In Emacs versions before 22, only Mouse-2 follows links and Mouse-1 always sets points. If you prefer this behavior, set the variable mouse-1-click-follows-link to nil. This variable also lets you choose various other alternatives for following links with the mouse. Type C-h v mouse-1-click-follows-link <RET> for more details.

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26.5 Mouse Clicks for Menus

Mouse clicks modified with the <CTRL> and <SHIFT> keys bring up menus.

This menu is for selecting a buffer.

The MSB (“mouse select buffer”) global minor mode makes this menu smarter and more customizable. See Buffer Menus.

This menu is for specifying faces and other text properties for editing formatted text. See Formatted Text.
This menu is mode-specific. For most modes if Menu-bar mode is on, this menu has the same items as all the mode-specific menu-bar menus put together. Some modes may specify a different menu for this button.3 If Menu-bar mode is off, this menu contains all the items which would be present in the menu bar—not just the mode-specific ones—so that you can access them without having to display the menu bar.
This menu is for specifying the frame's principal font.

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26.6 Mode Line Mouse Commands

You can use mouse clicks on window mode lines to select and manipulate windows.

Some areas of the mode line, such as the buffer name and the major mode name, have their own special mouse bindings. These areas are highlighted when you hold the mouse over them, and information about the special bindings will be displayed (see Tooltips).

You can also click on areas of the mode line that do not have special mouse bindings of their own. This has the following effects:

Mouse-1 on a mode line selects the window it belongs to. By dragging Mouse-1 on the mode line, you can move it, thus changing the height of the windows above and below.
Mouse-2 on a mode line expands that window to fill its frame.
Mouse-3 on a mode line deletes the window it belongs to. If the frame has only one window, it buries the current buffer instead, and switches to another buffer.
C-Mouse-2 on a mode line splits the window above horizontally, above the place in the mode line where you click.

C-Mouse-2 on a scroll bar splits the corresponding window vertically. See Split Window.

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26.7 Creating Frames

The prefix key C-x 5 is analogous to C-x 4, with parallel subcommands. The difference is that C-x 5 commands create a new frame rather than just a new window in the selected frame (see Pop Up Window). If an existing visible or iconified frame already displays the requested material, these commands use the existing frame, after raising or deiconifying as necessary.

The various C-x 5 commands differ in how they find or create the buffer to select:

C-x 5 2
Create a new frame (make-frame-command).
C-x 5 b bufname <RET>
Select buffer bufname in another frame. This runs switch-to-buffer-other-frame.
C-x 5 f filename <RET>
Visit file filename and select its buffer in another frame. This runs find-file-other-frame. See Visiting.
C-x 5 d directory <RET>
Select a Dired buffer for directory directory in another frame. This runs dired-other-frame. See Dired.
C-x 5 m
Start composing a mail message in another frame. This runs mail-other-frame. It is the other-frame variant of C-x m. See Sending Mail.
C-x 5 .
Find a tag in the current tag table in another frame. This runs find-tag-other-frame, the multiple-frame variant of M-.. See Tags.
C-x 5 r filename <RET>
Visit file filename read-only, and select its buffer in another frame. This runs find-file-read-only-other-frame. See Visiting.

You can control the appearance of new frames you create by setting the frame parameters in default-frame-alist. You can use the variable initial-frame-alist to specify parameters that affect only the initial frame. See Initial Parameters, for more information.

The easiest way to specify the principal font for all your Emacs frames is with an X resource (see Font X), but you can also do it by modifying default-frame-alist to specify the font parameter, as shown here:

     (add-to-list 'default-frame-alist '(font . "10x20"))

Here's a similar example for specifying a foreground color:

     (add-to-list 'default-frame-alist '(foreground-color . "blue"))

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26.8 Frame Commands

The following commands let you create, delete and operate on frames:

Iconify the selected Emacs frame (iconify-or-deiconify-frame). The normal meaning of C-z, to suspend Emacs, is not useful under a window system, so it has a different binding in that case.

If you type this command on an Emacs frame's icon, it deiconifies the frame.

C-x 5 0
Delete the selected frame (delete-frame). This is not allowed if there is only one frame.
C-x 5 o
Select another frame, raise it, and warp the mouse to it so that it stays selected. If you repeat this command, it cycles through all the frames on your terminal.
C-x 5 1
Delete all frames except the selected one.

To make the command C-x 5 o work properly, you must tell Emacs how the system (or the window manager) generally handles focus-switching between windows. There are two possibilities: either simply moving the mouse onto a window selects it (gives it focus), or you have to click on it in a suitable way to do so. Unfortunately there is no way Emacs can find out automatically which way the system handles this, so you have to explicitly say, by setting the variable focus-follows-mouse. If just moving the mouse onto a window selects it, that variable should be t; if a click is necessary, the variable should be nil.

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26.9 Speedbar Frames

The speedbar is a special frame for conveniently navigating in or operating on another frame. The speedbar, when it exists, is always associated with a specific frame, called its attached frame; all speedbar operations act on that frame.

Type M-x speedbar to create the speedbar and associate it with the current frame. To dismiss the speedbar, type M-x speedbar again, or select the speedbar and type q. (You can also delete the speedbar frame like any other Emacs frame.) If you wish to associate the speedbar with a different frame, dismiss it and call M-x speedbar from that frame.

The speedbar can operate in various modes. Its default mode is File Display mode, which shows the files in the current directory of the selected window of the attached frame, one file per line. Clicking on a file name visits that file in the selected window of the attached frame, and clicking on a directory name shows that directory in the speedbar (see Mouse References). Each line also has a box, ‘[+]’ or ‘<+>’, that you can click on to expand the contents of that item. Expanding a directory adds the contents of that directory to the speedbar display, underneath the directory's own line. Expanding an ordinary file adds a list of the tags in that file to the speedbar display; you can click on a tag name to jump to that tag in the selected window of the attached frame. When a file or directory is expanded, the ‘[+]’ changes to ‘[-]’; you can click on that box to contract the item, hiding its contents.

You navigate through the speedbar using the keyboard, too. Typing RET while point is on a line in the speedbar is equivalent to clicking the item on the current line, and SPC expands or contracts the item. U displays the parent directory of the current directory. To copy, delete, or rename the file on the current line, type C, D, and R respectively. To create a new directory, type M.

Another general-purpose speedbar mode is Buffer Display mode; in this mode, the speedbar displays a list of Emacs buffers. To switch to this mode, type b in the speedbar. To return to File Display mode, type f. You can also change the display mode by clicking mouse-3 anywhere in the speedbar window (or mouse-1 on the mode-line) and selecting ‘Displays’ in the pop-up menu.

Some major modes, including Rmail mode, Info, and GUD, have specialized ways of putting useful items into the speedbar for you to select. For example, in Rmail mode, the speedbar shows a list of Rmail files, and lets you move the current message to another Rmail file by clicking on its ‘<M>’ box.

For more details on using and programming the speedbar, See Speedbar.

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26.10 Multiple Displays

A single Emacs can talk to more than one X display. Initially, Emacs uses just one display—the one specified with the DISPLAY environment variable or with the ‘--display’ option (see Initial Options). To connect to another display, use the command make-frame-on-display:

M-x make-frame-on-display <RET> display <RET>
Create a new frame on display display.

A single X server can handle more than one screen. When you open frames on two screens belonging to one server, Emacs knows they share a single keyboard, and it treats all the commands arriving from these screens as a single stream of input.

When you open frames on different X servers, Emacs makes a separate input stream for each server. This way, two users can type simultaneously on the two displays, and Emacs will not garble their input. Each server also has its own selected frame. The commands you enter with a particular X server apply to that server's selected frame.

Despite these features, people using the same Emacs job from different displays can still interfere with each other if they are not careful. For example, if any one types C-x C-c, that exits the Emacs job for all of them!

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26.11 Special Buffer Frames

You can make certain chosen buffers, for which Emacs normally creates a second window when you have just one window, appear in special frames of their own. To do this, set the variable special-display-buffer-names to a list of buffer names; any buffer whose name is in that list automatically gets a special frame, when an Emacs command wants to display it “in another window.”

For example, if you set the variable this way,

     (setq special-display-buffer-names
           '("*Completions*" "*grep*" "*tex-shell*"))

then completion lists, grep output and the TeX mode shell buffer get individual frames of their own. These frames, and the windows in them, are never automatically split or reused for any other buffers. They continue to show the buffers they were created for, unless you alter them by hand. Killing the special buffer deletes its frame automatically.

More generally, you can set special-display-regexps to a list of regular expressions; then a buffer gets its own frame if its name matches any of those regular expressions. (Once again, this applies only to buffers that normally get displayed for you in a separate window.)

The variable special-display-frame-alist specifies the frame parameters for these frames. It has a default value, so you don't need to set it.

For those who know Lisp, an element of special-display-buffer-names or special-display-regexps can also be a list. Then the first element is the buffer name or regular expression; the rest of the list specifies how to create the frame. It can be an association list specifying frame parameter values; these values take precedence over parameter values specified in special-display-frame-alist. If you specify the symbol same-window as a “frame parameter” in this list, with a non-nil value, that means to use the selected window if possible. If you use the symbol same-frame as a “frame parameter” in this list, with a non-nil value, that means to use the selected frame if possible.

Alternatively, the value can have this form:

     (function args...)

where function is a symbol. Then the frame is constructed by calling function; its first argument is the buffer, and its remaining arguments are args.

An analogous feature lets you specify buffers which should be displayed in the selected window. See Force Same Window. The same-window feature takes precedence over the special-frame feature; therefore, if you add a buffer name to special-display-buffer-names and it has no effect, check to see whether that feature is also in use for the same buffer name.

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26.12 Setting Frame Parameters

This section describes commands for altering the display style and window management behavior of the selected frame.

M-x set-foreground-color <RET> color <RET>
Specify color color for the foreground of the selected frame. (This also changes the foreground color of the default face.) You can specify color either by its symbolic name or by its RGB numerical specification4.
M-x set-background-color <RET> color <RET>
Specify color color for the background of the selected frame. (This also changes the background color of the default face.)
M-x set-cursor-color <RET> color <RET>
Specify color color for the cursor of the selected frame.
M-x set-mouse-color <RET> color <RET>
Specify color color for the mouse cursor when it is over the selected frame.
M-x set-border-color <RET> color <RET>
Specify color color for the border of the selected frame.
M-x list-colors-display
Display the defined color names and show what the colors look like. This command is somewhat slow. See list-colors-display.
M-x auto-raise-mode
Toggle whether or not the selected frame should auto-raise. Auto-raise means that every time you move the mouse onto the frame, it raises the frame.

Note that this auto-raise feature is implemented by Emacs itself. Some window managers also implement auto-raise. If you enable auto-raise for Emacs frames in your X window manager, it should work, but it is beyond Emacs's control and therefore auto-raise-mode has no effect on it.

M-x auto-lower-mode
Toggle whether or not the selected frame should auto-lower. Auto-lower means that every time you move the mouse off the frame, the frame moves to the bottom of the stack of X windows.

The command auto-lower-mode has no effect on auto-lower implemented by the X window manager. To control that, you must use the appropriate window manager features.

M-x set-frame-font <RET> font <RET>
Specify font font as the principal font for the selected frame. The principal font controls several face attributes of the default face (see Faces). For example, if the principal font has a height of 12 pt, all text will be drawn in 12 pt fonts, unless you use another face that specifies a different height. See Font X, for ways to list the available fonts on your system.

You can also set a frame's principal font through a pop-up menu. Press S-Mouse-1 to activate this menu.

In Emacs versions that use an X toolkit, the color-setting and font-setting functions don't affect menus and the menu bar, since they are displayed by their own widget classes. To change the appearance of the menus and menu bar, you must use X resources (see Resources). See Colors, regarding colors. See Font X, regarding choice of font.

Colors, fonts, and other attributes of the frame's display can also be customized by setting frame parameters in the variable default-frame-alist (see Creating Frames). For a detailed description of frame parameters and customization, see Frame Parameters.

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26.13 Scroll Bars

When using X, Emacs normally makes a scroll bar at the left of each Emacs window.5 The scroll bar runs the height of the window, and shows a moving rectangular inner box which represents the portion of the buffer currently displayed. The entire height of the scroll bar represents the entire length of the buffer.

You can use Mouse-2 (normally, the middle button) in the scroll bar to move or drag the inner box up and down. If you move it to the top of the scroll bar, you see the top of the buffer. If you move it to the bottom of the scroll bar, you see the bottom of the buffer.

The left and right buttons in the scroll bar scroll by controlled increments. Mouse-1 (normally, the left button) moves the line at the level where you click up to the top of the window. Mouse-3 (normally, the right button) moves the line at the top of the window down to the level where you click. By clicking repeatedly in the same place, you can scroll by the same distance over and over.

You can also click C-Mouse-2 in the scroll bar to split a window vertically. The split occurs on the line where you click.

You can enable or disable Scroll Bar mode with the command M-x scroll-bar-mode. With no argument, it toggles the use of scroll bars. With an argument, it turns use of scroll bars on if and only if the argument is positive. This command applies to all frames, including frames yet to be created. Customize the variable scroll-bar-mode to control the use of scroll bars at startup. You can use it to specify that they are placed at the right of windows if you prefer that. You have to set this variable through the ‘Customize’ interface (see Easy Customization). Otherwise, it will not work properly. You can use the X resource ‘verticalScrollBars’ to control the initial setting of Scroll Bar mode similarly. See Resources.

To enable or disable scroll bars for just the selected frame, use the command M-x toggle-scroll-bar.

You can control the scroll bar width by changing the value of the scroll-bar-width frame parameter.

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26.14 Scrolling With “Wheeled” Mice

Some mice have a “wheel” instead of a third button. You can usually click the wheel to act as either Mouse-2 or Mouse-3, depending on the setup. You can also use the wheel to scroll windows instead of using the scroll bar or keyboard commands. Mouse wheel support only works if the system generates appropriate events; whenever possible, it is turned on by default. To toggle this feature, use M-x mouse-wheel-mode.

The variables mouse-wheel-follow-mouse and mouse-wheel-scroll-amount determine where and by how much buffers are scrolled. The variable mouse-wheel-progressive-speed determines whether the scroll speed is linked to how fast you move the wheel.

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26.15 Drag and Drop

Emacs supports drag and drop using the mouse. For instance, dropping text onto an Emacs frame inserts the text where it is dropped. Dropping a file onto an Emacs frame visits that file. As a special case, dropping the file on a Dired buffer moves or copies the file (according to the conventions of the application it came from) into the directory displayed in that buffer.

Dropping a file normally visits it in the window you drop it on. If you prefer to visit the file in a new window in such cases, customize the variable dnd-open-file-other-window.

The drag and drop protocols XDND, Motif and the old KDE 1.x protocol are currently supported.

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26.16 Menu Bars

You can turn display of menu bars on or off with M-x menu-bar-mode or by customizing the variable menu-bar-mode. With no argument, this command toggles Menu Bar mode, a minor mode. With an argument, the command turns Menu Bar mode on if the argument is positive, off if the argument is not positive. You can use the X resource ‘menuBarLines’ to control the initial setting of Menu Bar mode. See Resources.

Expert users often turn off the menu bar, especially on text-only terminals, where this makes one additional line available for text. If the menu bar is off, you can still pop up a menu of its contents with C-Mouse-3 on a display which supports pop-up menus. See Menu Mouse Clicks.

See Menu Bar, for information on how to invoke commands with the menu bar. See X Resources, for how to customize the menu bar menus.

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26.17 Tool Bars

The tool bar is a line (or lines) of icons at the top of the Emacs window, just below the menu bar. You can click on these icons with the mouse to do various jobs.

The global tool bar contains general commands. Some major modes define their own tool bars to replace it. A few “special” modes that are not designed for ordinary editing remove some items from the global tool bar.

Tool bars work only on a graphical display. The tool bar uses colored XPM icons if Emacs was built with XPM support. Otherwise, the tool bar uses monochrome icons (PBM or XBM format).

You can turn display of tool bars on or off with M-x tool-bar-mode or by customizing the option tool-bar-mode.

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26.18 Using Dialog Boxes

A dialog box is a special kind of menu for asking you a yes-or-no question or some other special question. Many Emacs commands use a dialog box to ask a yes-or-no question, if you used the mouse to invoke the command to begin with.

You can customize the variable use-dialog-box to suppress the use of dialog boxes. This also controls whether to use file selection windows (but those are not supported on all platforms).

A file selection window is a special kind of dialog box for asking for file names.

You can customize the variable use-file-dialog to suppress the use of file selection windows even if you still want other kinds of dialogs. This variable has no effect if you have suppressed all dialog boxes with the variable use-dialog-box.

For Gtk+ version 2.4 and 2.6, you can make Emacs use the old file dialog by setting the variable x-use-old-gtk-file-dialog to a non-nil value. If Emacs is built with a Gtk+ version that has only one file dialog, the setting of this variable has no effect.

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26.19 Tooltips

Tooltips are small windows that display text information at the current mouse position. They activate when there is a pause in mouse movement. There are two types of tooltip: help tooltips and GUD tooltips.

Help tooltips typically display over text—including the mode line—but may be also available for many other parts of the Emacs frame such as the tool bar and menu items.

You can toggle help tooltips (Tooltip mode) with the command M-x tooltip-mode. When Tooltip mode is disabled, the help text is displayed in the echo area instead.

GUD tooltips show values of variables. They are useful when you are debugging a program. See Debugger Operation.

The variables tooltip-delay specifies how long Emacs should wait before displaying a tooltip. For additional customization options for displaying tooltips, use M-x customize-group <RET> tooltip <RET>. See X Resources, for information on customizing the windows that display tooltips.

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26.20 Mouse Avoidance

Mouse Avoidance mode keeps the window system mouse pointer away from point, to avoid obscuring text. Whenever it moves the mouse, it also raises the frame. To use Mouse Avoidance mode, customize the variable mouse-avoidance-mode. You can set this to various values to move the mouse in several ways:

Move the mouse to the upper-right corner on any key-press;
Move the mouse to the corner only if the cursor gets too close, and allow it to return once the cursor is out of the way;
If the cursor gets too close to the mouse, displace the mouse a random distance & direction;
As jump, but shows steps along the way for illusion of motion;
The same as animate;
As animate, but changes the shape of the mouse pointer too.

You can also use the command M-x mouse-avoidance-mode to enable the mode.

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26.21 Non-Window Terminals

If your terminal does not have a window system that Emacs supports, then it can display only one Emacs frame at a time. However, you can still create multiple Emacs frames, and switch between them. Switching frames on these terminals is much like switching between different window configurations.

Use C-x 5 2 to create a new frame and switch to it; use C-x 5 o to cycle through the existing frames; use C-x 5 0 to delete the current frame.

Each frame has a number to distinguish it. If your terminal can display only one frame at a time, the selected frame's number n appears near the beginning of the mode line, in the form ‘Fn’.

Fn’ is actually the frame's name. You can also specify a different name if you wish, and you can select a frame by its name. Use the command M-x set-frame-name <RET> name <RET> to specify a new name for the selected frame, and use M-x select-frame-by-name <RET> name <RET> to select a frame according to its name. The name you specify appears in the mode line when the frame is selected.

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26.22 Using a Mouse in Terminal Emulators

Some terminal emulators under X support mouse clicks in the terminal window. In a terminal emulator which is compatible with xterm, you can use M-x xterm-mouse-mode to give Emacs control over simple use of the mouse—basically, only non-modified single clicks are supported. The normal xterm mouse functionality for such clicks is still available by holding down the SHIFT key when you press the mouse button.

Xterm Mouse mode is a global minor mode (see Minor Modes). Repeating the command turns the mode off again.

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27 International Character Set Support

Emacs supports a wide variety of international character sets, including European and Vietnamese variants of the Latin alphabet, as well as Cyrillic, Devanagari (for Hindi and Marathi), Ethiopic, Greek, Han (for Chinese and Japanese), Hangul (for Korean), Hebrew, IPA, Kannada, Lao, Malayalam, Tamil, Thai, Tibetan, and Vietnamese scripts. These features have been merged from the modified version of Emacs known as MULE (for “MULti-lingual Enhancement to GNU Emacs”)

Emacs also supports various encodings of these characters used by other internationalized software, such as word processors and mailers.

Emacs allows editing text with international characters by supporting all the related activities:

The rest of this chapter describes these issues in detail.

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27.1 Introduction to International Character Sets

The users of international character sets and scripts have established many more-or-less standard coding systems for storing files. Emacs internally uses a single multibyte character encoding, so that it can intermix characters from all these scripts in a single buffer or string. This encoding represents each non-ASCII character as a sequence of bytes in the range 0200 through 0377. Emacs translates between the multibyte character encoding and various other coding systems when reading and writing files, when exchanging data with subprocesses, and (in some cases) in the C-q command (see Multibyte Conversion).

The command C-h h (view-hello-file) displays the file etc/HELLO, which shows how to say “hello” in many languages. This illustrates various scripts. If some characters can't be displayed on your terminal, they appear as ‘?’ or as hollow boxes (see Undisplayable Characters).

Keyboards, even in the countries where these character sets are used, generally don't have keys for all the characters in them. So Emacs supports various input methods, typically one for each script or language, to make it convenient to type them.

The prefix key C-x <RET> is used for commands that pertain to multibyte characters, coding systems, and input methods.

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27.2 Enabling Multibyte Characters

You can enable or disable multibyte character support, either for Emacs as a whole, or for a single buffer. When multibyte characters are disabled in a buffer, then each byte in that buffer represents a character, even codes 0200 through 0377. The old features for supporting the European character sets, ISO Latin-1 and ISO Latin-2, work as they did in Emacs 19 and also work for the other ISO 8859 character sets.

However, there is no need to turn off multibyte character support to use ISO Latin; the Emacs multibyte character set includes all the characters in these character sets, and Emacs can translate automatically to and from the ISO codes.

By default, Emacs starts in multibyte mode, because that allows you to use all the supported languages and scripts without limitations.

To edit a particular file in unibyte representation, visit it using find-file-literally. See Visiting. To convert a buffer in multibyte representation into a single-byte representation of the same characters, the easiest way is to save the contents in a file, kill the buffer, and find the file again with find-file-literally. You can also use C-x <RET> c (universal-coding-system-argument) and specify ‘raw-text’ as the coding system with which to find or save a file. See Specify Coding. Finding a file as ‘raw-text’ doesn't disable format conversion, uncompression and auto mode selection as find-file-literally does.

To turn off multibyte character support by default, start Emacs with the ‘--unibyte’ option (see Initial Options), or set the environment variable EMACS_UNIBYTE. You can also customize enable-multibyte-characters or, equivalently, directly set the variable default-enable-multibyte-characters to nil in your init file to have basically the same effect as ‘--unibyte’.

To convert a unibyte session to a multibyte session, set default-enable-multibyte-characters to t. Buffers which were created in the unibyte session before you turn on multibyte support will stay unibyte. You can turn on multibyte support in a specific buffer by invoking the command toggle-enable-multibyte-characters in that buffer.

With ‘--unibyte’, multibyte strings are not created during initialization from the values of environment variables, /etc/passwd entries etc. that contain non-ASCII 8-bit characters.

Emacs normally loads Lisp files as multibyte, regardless of whether you used ‘--unibyte’. This includes the Emacs initialization file, .emacs, and the initialization files of Emacs packages such as Gnus. However, you can specify unibyte loading for a particular Lisp file, by putting ‘-*-unibyte: t;-*- in a comment on the first line (see File Variables). Then that file is always loaded as unibyte text, even if you did not start Emacs with ‘--unibyte’. The motivation for these conventions is that it is more reliable to always load any particular Lisp file in the same way. However, you can load a Lisp file as unibyte, on any one occasion, by typing C-x <RET> c raw-text <RET> immediately before loading it.

The mode line indicates whether multibyte character support is enabled in the current buffer. If it is, there are two or more characters (most often two dashes) before the colon near the beginning of the mode line. When multibyte characters are not enabled, just one dash precedes the colon.

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27.3 Language Environments

All supported character sets are supported in Emacs buffers whenever multibyte characters are enabled; there is no need to select a particular language in order to display its characters in an Emacs buffer. However, it is important to select a language environment in order to set various defaults. The language environment really represents a choice of preferred script (more or less) rather than a choice of language.

The language environment controls which coding systems to recognize when reading text (see Recognize Coding). This applies to files, incoming mail, netnews, and any other text you read into Emacs. It may also specify the default coding system to use when you create a file. Each language environment also specifies a default input method.

To select a language environment, you can customize the variable current-language-environment or use the command M-x set-language-environment. It makes no difference which buffer is current when you use this command, because the effects apply globally to the Emacs session. The supported language environments include:

Belarusian, Brazilian Portuguese, Bulgarian, Chinese-BIG5, Chinese-CNS, Chinese-EUC-TW, Chinese-GB, Croatian, Cyrillic-ALT, Cyrillic-ISO, Cyrillic-KOI8, Czech, Devanagari, Dutch, English, Ethiopic, French, Georgian, German, Greek, Hebrew, IPA, Italian, Japanese, Kannada, Korean, Lao, Latin-1, Latin-2, Latin-3, Latin-4, Latin-5, Latin-6, Latin-7, Latin-8 (Celtic), Latin-9 (updated Latin-1 with the Euro sign), Latvian, Lithuanian, Malayalam, Polish, Romanian, Russian, Slovak, Slovenian, Spanish, Swedish, Tajik, Tamil, Thai, Tibetan, Turkish, UTF-8 (for a setup which prefers Unicode characters and files encoded in UTF-8), Ukrainian, Vietnamese, Welsh, and Windows-1255 (for a setup which prefers Cyrillic characters and files encoded in Windows-1255).

To display the script(s) used by your language environment on a graphical display, you need to have a suitable font. If some of the characters appear as empty boxes, you should install the GNU Intlfonts package, which includes fonts for most supported scripts.6 See Fontsets, for more details about setting up your fonts.

Some operating systems let you specify the character-set locale you are using by setting the locale environment variables LC_ALL, LC_CTYPE, or LANG.7 During startup, Emacs looks up your character-set locale's name in the system locale alias table, matches its canonical name against entries in the value of the variables locale-charset-language-names and locale-language-names, and selects the corresponding language environment if a match is found. (The former variable overrides the latter.) It also adjusts the display table and terminal coding system, the locale coding system, the preferred coding system as needed for the locale, and—last but not least—the way Emacs decodes non-ASCII characters sent by your keyboard.

If you modify the LC_ALL, LC_CTYPE, or LANG environment variables while running Emacs, you may want to invoke the set-locale-environment function afterwards to readjust the language environment from the new locale.

The set-locale-environment function normally uses the preferred coding system established by the language environment to decode system messages. But if your locale matches an entry in the variable locale-preferred-coding-systems, Emacs uses the corresponding coding system instead. For example, if the locale ‘ja_JP.PCK’ matches japanese-shift-jis in locale-preferred-coding-systems, Emacs uses that encoding even though it might normally use japanese-iso-8bit.

You can override the language environment chosen at startup with explicit use of the command set-language-environment, or with customization of current-language-environment in your init file.

To display information about the effects of a certain language environment lang-env, use the command C-h L lang-env <RET> (describe-language-environment). This tells you which languages this language environment is useful for, and lists the character sets, coding systems, and input methods that go with it. It also shows some sample text to illustrate scripts used in this language environment. By default, this command describes the chosen language environment.

You can customize any language environment with the normal hook set-language-environment-hook. The command set-language-environment runs that hook after setting up the new language environment. The hook functions can test for a specific language environment by checking the variable current-language-environment. This hook is where you should put non-default settings for specific language environment, such as coding systems for keyboard input and terminal output, the default input method, etc.

Before it starts to set up the new language environment, set-language-environment first runs the hook exit-language-environment-hook. This hook is useful for undoing customizations that were made with set-language-environment-hook. For instance, if you set up a special key binding in a specific language environment using set-language-environment-hook, you should set up exit-language-environment-hook to restore the normal binding for that key.

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27.4 Input Methods

An input method is a kind of character conversion designed specifically for interactive input. In Emacs, typically each language has its own input method; sometimes several languages which use the same characters can share one input method. A few languages support several input methods.

The simplest kind of input method works by mapping ASCII letters into another alphabet; this allows you to use one other alphabet instead of ASCII. The Greek and Russian input methods work this way.

A more powerful technique is composition: converting sequences of characters into one letter. Many European input methods use composition to produce a single non-ASCII letter from a sequence that consists of a letter followed by accent characters (or vice versa). For example, some methods convert the sequence a' into a single accented letter. These input methods have no special commands of their own; all they do is compose sequences of printing characters.

The input methods for syllabic scripts typically use mapping followed by composition. The input methods for Thai and Korean work this way. First, letters are mapped into symbols for particular sounds or tone marks; then, sequences of these which make up a whole syllable are mapped into one syllable sign.

Chinese and Japanese require more complex methods. In Chinese input methods, first you enter the phonetic spelling of a Chinese word (in input method chinese-py, among others), or a sequence of portions of the character (input methods chinese-4corner and chinese-sw, and others). One input sequence typically corresponds to many possible Chinese characters. You select the one you mean using keys such as C-f, C-b, C-n, C-p, and digits, which have special meanings in this situation.

The possible characters are conceptually arranged in several rows, with each row holding up to 10 alternatives. Normally, Emacs displays just one row at a time, in the echo area; (i/j) appears at the beginning, to indicate that this is the ith row out of a total of j rows. Type C-n or C-p to display the next row or the previous row.

Type C-f and C-b to move forward and backward among the alternatives in the current row. As you do this, Emacs highlights the current alternative with a special color; type C-<SPC> to select the current alternative and use it as input. The alternatives in the row are also numbered; the number appears before the alternative. Typing a digit n selects the nth alternative of the current row and uses it as input.

<TAB> in these Chinese input methods displays a buffer showing all the possible characters at once; then clicking Mouse-2 on one of them selects that alternative. The keys C-f, C-b, C-n, C-p, and digits continue to work as usual, but they do the highlighting in the buffer showing the possible characters, rather than in the echo area.

In Japanese input methods, first you input a whole word using phonetic spelling; then, after the word is in the buffer, Emacs converts it into one or more characters using a large dictionary. One phonetic spelling corresponds to a number of different Japanese words; to select one of them, use C-n and C-p to cycle through the alternatives.

Sometimes it is useful to cut off input method processing so that the characters you have just entered will not combine with subsequent characters. For example, in input method latin-1-postfix, the sequence e ' combines to form an ‘e’ with an accent. What if you want to enter them as separate characters?

One way is to type the accent twice; this is a special feature for entering the separate letter and accent. For example, e ' ' gives you the two characters ‘e'’. Another way is to type another letter after the e—something that won't combine with that—and immediately delete it. For example, you could type e e <DEL> ' to get separate ‘e’ and ‘'’.

Another method, more general but not quite as easy to type, is to use C-\ C-\ between two characters to stop them from combining. This is the command C-\ (toggle-input-method) used twice.

C-\ C-\ is especially useful inside an incremental search, because it stops waiting for more characters to combine, and starts searching for what you have already entered.

To find out how to input the character after point using the current input method, type C-u C-x =. See Position Info.

The variables input-method-highlight-flag and input-method-verbose-flag control how input methods explain what is happening. If input-method-highlight-flag is non-nil, the partial sequence is highlighted in the buffer (for most input methods—some disable this feature). If input-method-verbose-flag is non-nil, the list of possible characters to type next is displayed in the echo area (but not when you are in the minibuffer).

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27.5 Selecting an Input Method

Enable or disable use of the selected input method.
C-x <RET> C-\ method <RET>
Select a new input method for the current buffer.
C-h I method <RET>
C-h C-\ method <RET>
Describe the input method method (describe-input-method). By default, it describes the current input method (if any). This description should give you the full details of how to use any particular input method.
M-x list-input-methods
Display a list of all the supported input methods.

To choose an input method for the current buffer, use C-x <RET> C-\ (set-input-method). This command reads the input method name from the minibuffer; the name normally starts with the language environment that it is meant to be used with. The variable current-input-method records which input method is selected.

Input methods use various sequences of ASCII characters to stand for non-ASCII characters. Sometimes it is useful to turn off the input method temporarily. To do this, type C-\ (toggle-input-method). To reenable the input method, type C-\ again.

If you type C-\ and you have not yet selected an input method, it prompts for you to specify one. This has the same effect as using C-x <RET> C-\ to specify an input method.

When invoked with a numeric argument, as in C-u C-\, toggle-input-method always prompts you for an input method, suggesting the most recently selected one as the default.

Selecting a language environment specifies a default input method for use in various buffers. When you have a default input method, you can select it in the current buffer by typing C-\. The variable default-input-method specifies the default input method (nil means there is none).

In some language environments, which support several different input methods, you might want to use an input method different from the default chosen by set-language-environment. You can instruct Emacs to select a different default input method for a certain language environment, if you wish, by using set-language-environment-hook (see set-language-environment-hook). For example:

     (defun my-chinese-setup ()
       "Set up my private Chinese environment."
       (if (equal current-language-environment "Chinese-GB")
           (setq default-input-method "chinese-tonepy")))
     (add-hook 'set-language-environment-hook 'my-chinese-setup)

This sets the default input method to be chinese-tonepy whenever you choose a Chinese-GB language environment.

Some input methods for alphabetic scripts work by (in effect) remapping the keyboard to emulate various keyboard layouts commonly used for those scripts. How to do this remapping properly depends on your actual keyboard layout. To specify which layout your keyboard has, use the command M-x quail-set-keyboard-layout.

You can use the command M-x quail-show-key to show what key (or key sequence) to type in order to input the character following point, using the selected keyboard layout. The command C-u C-x = also shows that information in addition to the other information about the character.

To display a list of all the supported input methods, type M-x list-input-methods. The list gives information about each input method, including the string that stands for it in the mode line.

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27.6 Unibyte and Multibyte Non-ASCII characters

When multibyte characters are enabled, character codes 0240 (octal) through 0377 (octal) are not really legitimate in the buffer. The valid non-ASCII printing characters have codes that start from 0400.

If you type a self-inserting character in the range 0240 through 0377, or if you use C-q to insert one, Emacs assumes you intended to use one of the ISO Latin-n character sets, and converts it to the Emacs code representing that Latin-n character. You select which ISO Latin character set to use through your choice of language environment If you do not specify a choice, the default is Latin-1.

If you insert a character in the range 0200 through 0237, which forms the eight-bit-control character set, it is inserted literally. You should normally avoid doing this since buffers containing such characters have to be written out in either the emacs-mule or raw-text coding system, which is usually not what you want.

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27.7 Coding Systems

Users of various languages have established many more-or-less standard coding systems for representing them. Emacs does not use these coding systems internally; instead, it converts from various coding systems to its own system when reading data, and converts the internal coding system to other coding systems when writing data. Conversion is possible in reading or writing files, in sending or receiving from the terminal, and in exchanging data with subprocesses.

Emacs assigns a name to each coding system. Most coding systems are used for one language, and the name of the coding system starts with the language name. Some coding systems are used for several languages; their names usually start with ‘iso’. There are also special coding systems no-conversion, raw-text and emacs-mule which do not convert printing characters at all.

A special class of coding systems, collectively known as codepages, is designed to support text encoded by MS-Windows and MS-DOS software. The names of these coding systems are cpnnnn, where nnnn is a 3- or 4-digit number of the codepage. You can use these encodings just like any other coding system; for example, to visit a file encoded in codepage 850, type C-x <RET> c cp850 <RET> C-x C-f filename <RET>8.

In addition to converting various representations of non-ASCII characters, a coding system can perform end-of-line conversion. Emacs handles three different conventions for how to separate lines in a file: newline, carriage-return linefeed, and just carriage-return.

C-h C coding <RET>
Describe coding system coding.
C-h C <RET>
Describe the coding systems currently in use.
M-x list-coding-systems
Display a list of all the supported coding systems.

The command C-h C (describe-coding-system) displays information about particular coding systems. You can specify a coding system name as the argument; alternatively, with an empty argument, it describes the coding systems currently selected for various purposes, both in the current buffer and as the defaults, and the priority list for recognizing coding systems (see Recognize Coding).

To display a list of all the supported coding systems, type M-x list-coding-systems. The list gives information about each coding system, including the letter that stands for it in the mode line (see Mode Line).

Each of the coding systems that appear in this list—except for no-conversion, which means no conversion of any kind—specifies how and whether to convert printing characters, but leaves the choice of end-of-line conversion to be decided based on the contents of each file. For example, if the file appears to use the sequence carriage-return linefeed to separate lines, DOS end-of-line conversion will be used.

Each of the listed coding systems has three variants which specify exactly what to do for end-of-line conversion:

Don't do any end-of-line conversion; assume the file uses newline to separate lines. (This is the convention normally used on Unix and GNU systems.)
Assume the file uses carriage-return linefeed to separate lines, and do the appropriate conversion. (This is the convention normally used on Microsoft systems.9)
Assume the file uses carriage-return to separate lines, and do the appropriate conversion. (This is the convention normally used on the Macintosh system.)

These variant coding systems are omitted from the list-coding-systems display for brevity, since they are entirely predictable. For example, the coding system iso-latin-1 has variants iso-latin-1-unix, iso-latin-1-dos and iso-latin-1-mac.

The coding system raw-text is good for a file which is mainly ASCII text, but may contain byte values above 127 which are not meant to encode non-ASCII characters. With raw-text, Emacs copies those byte values unchanged, and sets enable-multibyte-characters to nil in the current buffer so that they will be interpreted properly. raw-text handles end-of-line conversion in the usual way, based on the data encountered, and has the usual three variants to specify the kind of end-of-line conversion to use.

In contrast, the coding system no-conversion specifies no character code conversion at all—none for non-ASCII byte values and none for end of line. This is useful for reading or writing binary files, tar files, and other files that must be examined verbatim. It, too, sets enable-multibyte-characters to nil.

The easiest way to edit a file with no conversion of any kind is with the M-x find-file-literally command. This uses no-conversion, and also suppresses other Emacs features that might convert the file contents before you see them. See Visiting.

The coding system emacs-mule means that the file contains non-ASCII characters stored with the internal Emacs encoding. It handles end-of-line conversion based on the data encountered, and has the usual three variants to specify the kind of end-of-line conversion.

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27.8 Recognizing Coding Systems

Emacs tries to recognize which coding system to use for a given text as an integral part of reading that text. (This applies to files being read, output from subprocesses, text from X selections, etc.) Emacs can select the right coding system automatically most of the time—once you have specified your preferences.

Some coding systems can be recognized or distinguished by which byte sequences appear in the data. However, there are coding systems that cannot be distinguished, not even potentially. For example, there is no way to distinguish between Latin-1 and Latin-2; they use the same byte values with different meanings.

Emacs handles this situation by means of a priority list of coding systems. Whenever Emacs reads a file, if you do not specify the coding system to use, Emacs checks the data against each coding system, starting with the first in priority and working down the list, until it finds a coding system that fits the data. Then it converts the file contents assuming that they are represented in this coding system.

The priority list of coding systems depends on the selected language environment (see Language Environments). For example, if you use French, you probably want Emacs to prefer Latin-1 to Latin-2; if you use Czech, you probably want Latin-2 to be preferred. This is one of the reasons to specify a language environment.

However, you can alter the coding system priority list in detail with the command M-x prefer-coding-system. This command reads the name of a coding system from the minibuffer, and adds it to the front of the priority list, so that it is preferred to all others. If you use this command several times, each use adds one element to the front of the priority list.

If you use a coding system that specifies the end-of-line conversion type, such as iso-8859-1-dos, what this means is that Emacs should attempt to recognize iso-8859-1 with priority, and should use DOS end-of-line conversion when it does recognize iso-8859-1.

Sometimes a file name indicates which coding system to use for the file. The variable file-coding-system-alist specifies this correspondence. There is a special function modify-coding-system-alist for adding elements to this list. For example, to read and write all ‘.txt’ files using the coding system china-iso-8bit, you can execute this Lisp expression:

     (modify-coding-system-alist 'file "\\.txt\\'" 'chinese-iso-8bit)

The first argument should be file, the second argument should be a regular expression that determines which files this applies to, and the third argument says which coding system to use for these files.

Emacs recognizes which kind of end-of-line conversion to use based on the contents of the file: if it sees only carriage-returns, or only carriage-return linefeed sequences, then it chooses the end-of-line conversion accordingly. You can inhibit the automatic use of end-of-line conversion by setting the variable inhibit-eol-conversion to non-nil. If you do that, DOS-style files will be displayed with the ‘^M’ characters visible in the buffer; some people prefer this to the more subtle ‘(DOS)’ end-of-line type indication near the left edge of the mode line (see eol-mnemonic).

By default, the automatic detection of coding system is sensitive to escape sequences. If Emacs sees a sequence of characters that begin with an escape character, and the sequence is valid as an ISO-2022 code, that tells Emacs to use one of the ISO-2022 encodings to decode the file.

However, there may be cases that you want to read escape sequences in a file as is. In such a case, you can set the variable inhibit-iso-escape-detection to non-nil. Then the code detection ignores any escape sequences, and never uses an ISO-2022 encoding. The result is that all escape sequences become visible in the buffer.

The default value of inhibit-iso-escape-detection is nil. We recommend that you not change it permanently, only for one specific operation. That's because many Emacs Lisp source files in the Emacs distribution contain non-ASCII characters encoded in the coding system iso-2022-7bit, and they won't be decoded correctly when you visit those files if you suppress the escape sequence detection.

You can specify the coding system for a particular file using the ‘-*-...-*- construct at the beginning of a file, or a local variables list at the end (see File Variables). You do this by defining a value for the “variable” named coding. Emacs does not really have a variable coding; instead of setting a variable, this uses the specified coding system for the file. For example, ‘-*-mode: C; coding: latin-1;-*-’ specifies use of the Latin-1 coding system, as well as C mode. When you specify the coding explicitly in the file, that overrides file-coding-system-alist.

The variables auto-coding-alist, auto-coding-regexp-alist and auto-coding-functions are the strongest way to specify the coding system for certain patterns of file names, or for files containing certain patterns; these variables even override ‘-*-coding:-*-’ tags in the file itself. Emacs uses auto-coding-alist for tar and archive files, to prevent it from being confused by a ‘-*-coding:-*-’ tag in a member of the archive and thinking it applies to the archive file as a whole. Likewise, Emacs uses auto-coding-regexp-alist to ensure that RMAIL files, whose names in general don't match any particular pattern, are decoded correctly. One of the builtin auto-coding-functions detects the encoding for XML files.

If Emacs recognizes the encoding of a file incorrectly, you can reread the file using the correct coding system by typing C-x <RET> r coding-system <RET>. To see what coding system Emacs actually used to decode the file, look at the coding system mnemonic letter near the left edge of the mode line (see Mode Line), or type C-h C <RET>.

The command unify-8859-on-decoding-mode enables a mode that “unifies” the Latin alphabets when decoding text. This works by converting all non-ASCII Latin-n characters to either Latin-1 or Unicode characters. This way it is easier to use various Latin-n alphabets together. In a future Emacs version we hope to move towards full Unicode support and complete unification of character sets.

Once Emacs has chosen a coding system for a buffer, it stores that coding system in buffer-file-coding-system and uses that coding system, by default, for operations that write from this buffer into a file. This includes the commands save-buffer and write-region. If you want to write files from this buffer using a different coding system, you can specify a different coding system for the buffer using set-buffer-file-coding-system (see Specify Coding).

You can insert any possible character into any Emacs buffer, but most coding systems can only handle some of the possible characters. This means that it is possible for you to insert characters that cannot be encoded with the coding system that will be used to save the buffer. For example, you could start with an ASCII file and insert a few Latin-1 characters into it, or you could edit a text file in Polish encoded in iso-8859-2 and add some Russian words to it. When you save the buffer, Emacs cannot use the current value of buffer-file-coding-system, because the characters you added cannot be encoded by that coding system.

When that happens, Emacs tries the most-preferred coding system (set by M-x prefer-coding-system or M-x set-language-environment), and if that coding system can safely encode all of the characters in the buffer, Emacs uses it, and stores its value in buffer-file-coding-system. Otherwise, Emacs displays a list of coding systems suitable for encoding the buffer's contents, and asks you to choose one of those coding systems.

If you insert the unsuitable characters in a mail message, Emacs behaves a bit differently. It additionally checks whether the most-preferred coding system is recommended for use in MIME messages; if not, Emacs tells you that the most-preferred coding system is not recommended and prompts you for another coding system. This is so you won't inadvertently send a message encoded in a way that your recipient's mail software will have difficulty decoding. (If you do want to use the most-preferred coding system, you can still type its name in response to the question.)

When you send a message with Mail mode (see Sending Mail), Emacs has four different ways to determine the coding system to use for encoding the message text. It tries the buffer's own value of buffer-file-coding-system, if that is non-nil. Otherwise, it uses the value of sendmail-coding-system, if that is non-nil. The third way is to use the default coding system for new files, which is controlled by your choice of language environment, if that is non-nil. If all of these three values are nil, Emacs encodes outgoing mail using the Latin-1 coding system.

When you get new mail in Rmail, each message is translated automatically from the coding system it is written in, as if it were a separate file. This uses the priority list of coding systems that you have specified. If a MIME message specifies a character set, Rmail obeys that specification, unless rmail-decode-mime-charset is nil.

For reading and saving Rmail files themselves, Emacs uses the coding system specified by the variable rmail-file-coding-system. The default value is nil, which means that Rmail files are not translated (they are read and written in the Emacs internal character code).

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27.9 Specifying a Coding System

In cases where Emacs does not automatically choose the right coding system, you can use these commands to specify one:

C-x <RET> f coding <RET>
Use coding system coding for saving or revisiting the visited file in the current buffer.
C-x <RET> c coding <RET>
Specify coding system coding for the immediately following command.
C-x <RET> r coding <RET>
Revisit the current file using the coding system coding.
C-x <RET> k coding <RET>
Use coding system coding for keyboard input.
C-x <RET> t coding <RET>
Use coding system coding for terminal output.
C-x <RET> p input-coding <RET> output-coding <RET>
Use coding systems input-coding and output-coding for subprocess input and output in the current buffer.
C-x <RET> x coding <RET>
Use coding system coding for transferring selections to and from other programs through the window system.
C-x <RET> F coding <RET>
Use coding system coding for encoding and decoding file names. This affects the use of non-ASCII characters in file names. It has no effect on reading and writing the contents of files.
C-x <RET> X coding <RET>
Use coding system coding for transferring one selection—the next one—to or from the window system.
M-x recode-region
Convert the region from a previous coding system to a new one.

The command C-x <RET> f (set-buffer-file-coding-system) sets the file coding system for the current buffer—in other words, it says which coding system to use when saving or reverting the visited file. You specify which coding system using the minibuffer. If you specify a coding system that cannot handle all of the characters in the buffer, Emacs warns you about the troublesome characters when you actually save the buffer.

Another way to specify the coding system for a file is when you visit the file. First use the command C-x <RET> c (universal-coding-system-argument); this command uses the minibuffer to read a coding system name. After you exit the minibuffer, the specified coding system is used for the immediately following command.

So if the immediately following command is C-x C-f, for example, it reads the file using that coding system (and records the coding system for when you later save the file). Or if the immediately following command is C-x C-w, it writes the file using that coding system. When you specify the coding system for saving in this way, instead of with C-x <RET> f, there is no warning if the buffer contains characters that the coding system cannot handle.

Other file commands affected by a specified coding system include C-x C-i and C-x C-v, as well as the other-window variants of C-x C-f. C-x <RET> c also affects commands that start subprocesses, including M-x shell (see Shell).

If the immediately following command does not use the coding system, then C-x <RET> c ultimately has no effect.

An easy way to visit a file with no conversion is with the M-x find-file-literally command. See Visiting.

The variable default-buffer-file-coding-system specifies the choice of coding system to use when you create a new file. It applies when you find a new file, and when you create a buffer and then save it in a file. Selecting a language environment typically sets this variable to a good choice of default coding system for that language environment.

If you visit a file with a wrong coding system, you can correct this with C-x <RET> r (revert-buffer-with-coding-system). This visits the current file again, using a coding system you specify.

The command C-x <RET> t (set-terminal-coding-system) specifies the coding system for terminal output. If you specify a character code for terminal output, all characters output to the terminal are translated into that coding system.

This feature is useful for certain character-only terminals built to support specific languages or character sets—for example, European terminals that support one of the ISO Latin character sets. You need to specify the terminal coding system when using multibyte text, so that Emacs knows which characters the terminal can actually handle.

By default, output to the terminal is not translated at all, unless Emacs can deduce the proper coding system from your terminal type or your locale specification (see Language Environments).

The command C-x <RET> k (set-keyboard-coding-system) or the variable keyboard-coding-system specifies the coding system for keyboard input. Character-code translation of keyboard input is useful for terminals with keys that send non-ASCII graphic characters—for example, some terminals designed for ISO Latin-1 or subsets of it.

By default, keyboard input is translated based on your system locale setting. If your terminal does not really support the encoding implied by your locale (for example, if you find it inserts a non-ASCII character if you type M-i), you will need to set keyboard-coding-system to nil to turn off encoding. You can do this by putting

     (set-keyboard-coding-system nil)

in your ~/.emacs file.

There is a similarity between using a coding system translation for keyboard input, and using an input method: both define sequences of keyboard input that translate into single characters. However, input methods are designed to be convenient for interactive use by humans, and the sequences that are translated are typically sequences of ASCII printing characters. Coding systems typically translate sequences of non-graphic characters.

The command C-x <RET> x (set-selection-coding-system) specifies the coding system for sending selected text to the window system, and for receiving the text of selections made in other applications. This command applies to all subsequent selections, until you override it by using the command again. The command C-x <RET> X (set-next-selection-coding-system) specifies the coding system for the next selection made in Emacs or read by Emacs.

The command C-x <RET> p (set-buffer-process-coding-system) specifies the coding system for input and output to a subprocess. This command applies to the current buffer; normally, each subprocess has its own buffer, and thus you can use this command to specify translation to and from a particular subprocess by giving the command in the corresponding buffer.

The default for translation of process input and output depends on the current language environment.

If a piece of text has already been inserted into a buffer using the wrong coding system, you can decode it again using M-x recode-region. This prompts you for the old coding system and the desired coding system, and acts on the text in the region.

The variable file-name-coding-system specifies a coding system to use for encoding file names. If you set the variable to a coding system name (as a Lisp symbol or a string), Emacs encodes file names using that coding system for all file operations. This makes it possible to use non-ASCII characters in file names—or, at least, those non-ASCII characters which the specified coding system can encode. Use C-x <RET> F (set-file-name-coding-system) to specify this interactively.

If file-name-coding-system is nil, Emacs uses a default coding system determined by the selected language environment. In the default language environment, any non-ASCII characters in file names are not encoded specially; they appear in the file system using the internal Emacs representation.

Warning: if you change file-name-coding-system (or the language environment) in the middle of an Emacs session, problems can result if you have already visited files whose names were encoded using the earlier coding system and cannot be encoded (or are encoded differently) under the new coding system. If you try to save one of these buffers under the visited file name, saving may use the wrong file name, or it may get an error. If such a problem happens, use C-x C-w to specify a new file name for that buffer.

If a mistake occurs when encoding a file name, use the command M-x recode-file-name to change the file name's coding system. This prompts for an existing file name, its old coding system, and the coding system to which you wish to convert.

The variable locale-coding-system specifies a coding system to use when encoding and decoding system strings such as system error messages and format-time-string formats and time stamps. That coding system is also used for decoding non-ASCII keyboard input on X Window systems. You should choose a coding system that is compatible with the underlying system's text representation, which is normally specified by one of the environment variables LC_ALL, LC_CTYPE, and LANG. (The first one, in the order specified above, whose value is nonempty is the one that determines the text representation.)

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27.10 Fontsets

A font for X typically defines shapes for a single alphabet or script. Therefore, displaying the entire range of scripts that Emacs supports requires a collection of many fonts. In Emacs, such a collection is called a fontset. A fontset is defined by a list of fonts, each assigned to handle a range of character codes.

Each fontset has a name, like a font. The available X fonts are defined by the X server; fontsets, however, are defined within Emacs itself. Once you have defined a fontset, you can use it within Emacs by specifying its name, anywhere that you could use a single font. Of course, Emacs fontsets can use only the fonts that the X server supports; if certain characters appear on the screen as hollow boxes, this means that the fontset in use for them has no font for those characters.10

Emacs creates two fontsets automatically: the standard fontset and the startup fontset. The standard fontset is most likely to have fonts for a wide variety of non-ASCII characters; however, this is not the default for Emacs to use. (By default, Emacs tries to find a font that has bold and italic variants.) You can specify use of the standard fontset with the ‘-fn’ option, or with the ‘Font’ X resource (see Font X). For example,

     emacs -fn fontset-standard

A fontset does not necessarily specify a font for every character code. If a fontset specifies no font for a certain character, or if it specifies a font that does not exist on your system, then it cannot display that character properly. It will display that character as an empty box instead.

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27.11 Defining fontsets

Emacs creates a standard fontset automatically according to the value of standard-fontset-spec. This fontset's name is


or just ‘fontset-standard’ for short.

Bold, italic, and bold-italic variants of the standard fontset are created automatically. Their names have ‘bold’ instead of ‘medium’, or ‘i’ instead of ‘r’, or both.

If you specify a default ASCII font with the ‘Font’ resource or the ‘-fn’ argument, Emacs generates a fontset from it automatically. This is the startup fontset and its name is fontset-startup. It does this by replacing the foundry, family, add_style, and average_width fields of the font name with ‘*’, replacing charset_registry field with ‘fontset’, and replacing charset_encoding field with ‘startup’, then using the resulting string to specify a fontset.

For instance, if you start Emacs this way,

     emacs -fn "*courier-medium-r-normal--14-140-*-iso8859-1"

Emacs generates the following fontset and uses it for the initial X window frame:


With the X resource ‘Emacs.Font’, you can specify a fontset name just like an actual font name. But be careful not to specify a fontset name in a wildcard resource like ‘Emacs*Font’—that wildcard specification matches various other resources, such as for menus, and menus cannot handle fontsets.

You can specify additional fontsets using X resources named ‘Fontset-n’, where n is an integer starting from 0. The resource value should have this form:

     fontpattern, [charsetname:fontname]...

fontpattern should have the form of a standard X font name, except for the last two fields. They should have the form ‘fontset-alias’.

The fontset has two names, one long and one short. The long name is fontpattern. The short name is ‘fontset-alias’. You can refer to the fontset by either name.

The construct ‘charset:font’ specifies which font to use (in this fontset) for one particular character set. Here, charset is the name of a character set, and font is the font to use for that character set. You can use this construct any number of times in defining one fontset.

For the other character sets, Emacs chooses a font based on fontpattern. It replaces ‘fontset-alias’ with values that describe the character set. For the ASCII character font, ‘fontset-alias’ is replaced with ‘ISO8859-1’.

In addition, when several consecutive fields are wildcards, Emacs collapses them into a single wildcard. This is to prevent use of auto-scaled fonts. Fonts made by scaling larger fonts are not usable for editing, and scaling a smaller font is not useful because it is better to use the smaller font in its own size, which is what Emacs does.

Thus if fontpattern is this,


the font specification for ASCII characters would be this:


and the font specification for Chinese GB2312 characters would be this:


You may not have any Chinese font matching the above font specification. Most X distributions include only Chinese fonts that have ‘song ti’ or ‘fangsong ti’ in family field. In such a case, ‘Fontset-n’ can be specified as below:

     Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\

Then, the font specifications for all but Chinese GB2312 characters have ‘fixed’ in the family field, and the font specification for Chinese GB2312 characters has a wild card ‘*’ in the family field.

The function that processes the fontset resource value to create the fontset is called create-fontset-from-fontset-spec. You can also call this function explicitly to create a fontset.

See Font X, for more information about font naming in X.

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27.12 Undisplayable Characters

There may be a some non-ASCII characters that your terminal cannot display. Most non-windowing terminals support just a single character set (use the variable default-terminal-coding-system (see Specify Coding) to tell Emacs which one); characters which can't be encoded in that coding system are displayed as ‘?’ by default.

Windowing terminals can display a broader range of characters, but you may not have fonts installed for all of them; characters that have no font appear as a hollow box.

If you use Latin-1 characters but your terminal can't display Latin-1, you can arrange to display mnemonic ASCII sequences instead, e.g. ‘"o’ for o-umlaut. Load the library iso-ascii to do this.

If your terminal can display Latin-1, you can display characters from other European character sets using a mixture of equivalent Latin-1 characters and ASCII mnemonics. Customize the variable latin1-display to enable this. The mnemonic ASCII sequences mostly correspond to those of the prefix input methods.

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27.13 Single-byte Character Set Support

The ISO 8859 Latin-n character sets define character codes in the range 0240 to 0377 octal (160 to 255 decimal) to handle the accented letters and punctuation needed by various European languages (and some non-European ones). If you disable multibyte characters, Emacs can still handle one of these character codes at a time. To specify which of these codes to use, invoke M-x set-language-environment and specify a suitable language environment such as ‘Latin-n’.

For more information about unibyte operation, see Enabling Multibyte. Note particularly that you probably want to ensure that your initialization files are read as unibyte if they contain non-ASCII characters.

Emacs can also display those characters, provided the terminal or font in use supports them. This works automatically. Alternatively, if you are using a window system, Emacs can also display single-byte characters through fontsets, in effect by displaying the equivalent multibyte characters according to the current language environment. To request this, set the variable unibyte-display-via-language-environment to a non-nil value.

If your terminal does not support display of the Latin-1 character set, Emacs can display these characters as ASCII sequences which at least give you a clear idea of what the characters are. To do this, load the library iso-ascii. Similar libraries for other Latin-n character sets could be implemented, but we don't have them yet.

Normally non-ISO-8859 characters (decimal codes between 128 and 159 inclusive) are displayed as octal escapes. You can change this for non-standard “extended” versions of ISO-8859 character sets by using the function standard-display-8bit in the disp-table library.

There are two ways to input single-byte non-ASCII characters:

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27.14 Charsets

Emacs groups all supported characters into disjoint charsets. Each character code belongs to one and only one charset. For historical reasons, Emacs typically divides an 8-bit character code for an extended version of ASCII into two charsets: ASCII, which covers the codes 0 through 127, plus another charset which covers the “right-hand part” (the codes 128 and up). For instance, the characters of Latin-1 include the Emacs charset ascii plus the Emacs charset latin-iso8859-1.

Emacs characters belonging to different charsets may look the same, but they are still different characters. For example, the letter ‘o’ with acute accent in charset latin-iso8859-1, used for Latin-1, is different from the letter ‘o’ with acute accent in charset latin-iso8859-2, used for Latin-2.

There are two commands for obtaining information about Emacs charsets. The command M-x list-charset-chars prompts for a name of a character set, and displays all the characters in that character set. The command M-x describe-character-set prompts for a charset name and displays information about that charset, including its internal representation within Emacs.

To find out which charset a character in the buffer belongs to, put point before it and type C-u C-x =.

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28 Major Modes

Emacs provides many alternative major modes, each of which customizes Emacs for editing text of a particular sort. The major modes are mutually exclusive, and each buffer has one major mode at any time. The mode line normally shows the name of the current major mode, in parentheses (see Mode Line).

The least specialized major mode is called Fundamental mode. This mode has no mode-specific redefinitions or variable settings, so that each Emacs command behaves in its most general manner, and each user option variable is in its default state. For editing text of a specific type that Emacs knows about, such as Lisp code or English text, you should switch to the appropriate major mode, such as Lisp mode or Text mode.

Selecting a major mode changes the meanings of a few keys to become more specifically adapted to the language being edited. The ones that are changed frequently are <TAB>, <DEL>, and C-j. The prefix key C-c normally contains mode-specific commands. In addition, the commands which handle comments use the mode to determine how comments are to be delimited. Many major modes redefine the syntactical properties of characters appearing in the buffer. See Syntax.

The major modes fall into three major groups. The first group contains modes for normal text, either plain or with mark-up. It includes Text mode, HTML mode, SGML mode, TeX mode and Outline mode. The second group contains modes for specific programming languages. These include Lisp mode (which has several variants), C mode, Fortran mode, and others. The remaining major modes are not intended for use on users' files; they are used in buffers created for specific purposes by Emacs, such as Dired mode for buffers made by Dired (see Dired), Mail mode for buffers made by C-x m (see Sending Mail), and Shell mode for buffers used for communicating with an inferior shell process (see Interactive Shell).

Most programming-language major modes specify that only blank lines separate paragraphs. This is to make the paragraph commands useful. (See Paragraphs.) They also cause Auto Fill mode to use the definition of <TAB> to indent the new lines it creates. This is because most lines in a program are usually indented (see Indentation).

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28.1 How Major Modes are Chosen

You can select a major mode explicitly for the current buffer, but most of the time Emacs determines which mode to use based on the file name or on special text in the file.

Explicit selection of a new major mode is done with a M-x command. From the name of a major mode, add -mode to get the name of a command to select that mode. Thus, you can enter Lisp mode by executing M-x lisp-mode.

When you visit a file, Emacs usually chooses the right major mode based on the file's name. For example, files whose names end in ‘.c’ are edited in C mode. The correspondence between file names and major modes is controlled by the variable auto-mode-alist. Its value is a list in which each element has this form,

     (regexp . mode-function)

or this form,

     (regexp mode-function flag)

For example, one element normally found in the list has the form ("\\.c\\'" . c-mode), and it is responsible for selecting C mode for files whose names end in .c. (Note that ‘\\’ is needed in Lisp syntax to include a ‘\’ in the string, which must be used to suppress the special meaning of ‘.’ in regexps.) If the element has the form (regexp mode-function flag) and flag is non-nil, then after calling mode-function, Emacs discards the suffix that matched regexp and searches the list again for another match.

Sometimes the major mode is determined from the way the file's text begins. The variable magic-mode-alist controls this. Its value is a list of elements of this form:

     (regexp . mode-function)

This looks like an element of auto-mode-alist, but it doesn't work the same: this regexp is matched against the text at the start of the buffer, not against the file name. magic-mode-alist takes priority over auto-mode-alist.

You can specify the major mode to use for editing a certain file by special text in the first nonblank line of the file. The mode name should appear in this line both preceded and followed by ‘-*-’. Other text may appear on the line as well. For example,


tells Emacs to use Lisp mode. Such an explicit specification overrides any defaults based on the file name. Note how the semicolon is used to make Lisp treat this line as a comment.

Another format of mode specification is

     -*- mode: modename;-*-

which allows you to specify local variables as well, like this:

     -*- mode: modename; var: value; ... -*-

See File Variables, for more information about this.

When a file's contents begin with ‘#!’, it can serve as an executable shell command, which works by running an interpreter named on the file's first line. The rest of the file is used as input to the interpreter.

When you visit such a file in Emacs, if the file's name does not specify a major mode, Emacs uses the interpreter name on the first line to choose a mode. If the first line is the name of a recognized interpreter program, such as ‘perl’ or ‘tcl’, Emacs uses a mode appropriate for programs for that interpreter. The variable interpreter-mode-alist specifies the correspondence between interpreter program names and major modes.

When the first line starts with ‘#!’, you cannot (on many systems) use the ‘-*-’ feature on the first line, because the system would get confused when running the interpreter. So Emacs looks for ‘-*-’ on the second line in such files as well as on the first line.

When you visit a file that does not specify a major mode to use, or when you create a new buffer with C-x b, the variable default-major-mode specifies which major mode to use. Normally its value is the symbol fundamental-mode, which specifies Fundamental mode. If default-major-mode is nil, the major mode is taken from the previously current buffer.

If you change the major mode of a buffer, you can go back to the major mode Emacs would choose automatically: use the command M-x normal-mode to do this. This is the same function that find-file calls to choose the major mode. It also processes the file's ‘-*-’ line or local variables list (if any). See File Variables.

The commands C-x C-w and set-visited-file-name change to a new major mode if the new file name implies a mode (see Saving). (C-x C-s does this too, if the buffer wasn't visiting a file.) However, this does not happen if the buffer contents specify a major mode, and certain “special” major modes do not allow the mode to change. You can turn off this mode-changing feature by setting change-major-mode-with-file-name to nil.

Next: , Previous: Major Modes, Up: Top

29 Indentation

This chapter describes the Emacs commands that add, remove, or adjust indentation.

Indent the current line “appropriately” in a mode-dependent fashion.
Perform <RET> followed by <TAB> (newline-and-indent).
Merge the previous and the current line (delete-indentation). This would cancel the effect of a preceding C-j.
Split the current line at point; text on the line after point becomes a new line indented to the same column where point is located (split-line).
Move (forward or back) to the first nonblank character on the current line (back-to-indentation).
Indent lines in the region to the same column (indent-region).
C-x <TAB>
Shift lines in the region rigidly right or left (indent-rigidly).
Indent from point to the next prespecified tab stop column (tab-to-tab-stop).
M-x indent-relative
Indent from point to under an indentation point in the previous line.

Emacs supports four general categories of operations that could all be called `indentation':

  1. Insert a tab character. You can type C-q <TAB> to do this.

    A tab character is displayed as a stretch of whitespace which extends to the next display tab stop position, and the default width of a tab stop is eight. See Display Custom, for more details.

  2. Insert whitespace up to the next tab stop. You can set tab stops at your choice of column positions, then type M-i to advance to the next tab stop. The default tab stop settings have a tab stop every eight columns, which means by default M-i inserts a tab character. To set the tab stops, use M-x edit-tab-stops.
  3. Align a line with the previous line. More precisely, the command M-x indent-relative indents the current line under the beginning of some word in the previous line. In Fundamental mode and in Text mode, <TAB> runs the command indent-relative.
  4. The most sophisticated method is syntax-driven indentation. Most programming languages have an indentation convention. For Lisp code, lines are indented according to their nesting in parentheses. C code uses the same general idea, but many details are different.

    Type <TAB> to do syntax-driven indentation, in a mode that supports it. It realigns the current line according with the syntax of the preceding lines. No matter where in the line you are when you type <TAB>, it aligns the line as a whole.

Normally, most of the above methods insert an optimal mix of tabs and spaces to align to the desired column. See Just Spaces, for how to disable use of tabs. However, C-q <TAB> always inserts a tab, even when tabs are disabled for the indentation commands.

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29.1 Indentation Commands and Techniques

To move over the indentation on a line, do M-m (back-to-indentation). This command, given anywhere on a line, positions point at the first nonblank character on the line, if any, or else at the end of the line.

To insert an indented line before the current line, do C-a C-o <TAB>. To make an indented line after the current line, use C-e C-j.

If you just want to insert a tab character in the buffer, you can type C-q <TAB>.

C-M-o (split-line) moves the text from point to the end of the line vertically down, so that the current line becomes two lines. C-M-o first moves point forward over any spaces and tabs. Then it inserts after point a newline and enough indentation to reach the same column point is on. Point remains before the inserted newline; in this regard, C-M-o resembles C-o.

To join two lines cleanly, use the M-^ (delete-indentation) command. It deletes the indentation at the front of the current line, and the line boundary as well, replacing them with a single space. As a special case (useful for Lisp code) the single space is omitted if the characters to be joined are consecutive open parentheses or closing parentheses, or if the junction follows another newline. To delete just the indentation of a line, go to the beginning of the line and use M-\ (delete-horizontal-space), which deletes all spaces and tabs around the cursor.

If you have a fill prefix, M-^ deletes the fill prefix if it appears after the newline that is deleted. See Fill Prefix.

There are also commands for changing the indentation of several lines at once. They apply to all the lines that begin in the region. C-M-\ (indent-region) indents each line in the “usual” way, as if you had typed <TAB> at the beginning of the line. A numeric argument specifies the column to indent to, and each line is shifted left or right so that its first nonblank character appears in that column. C-x <TAB> (indent-rigidly) moves all of the lines in the region right by its argument (left, for negative arguments). The whole group of lines moves rigidly sideways, which is how the command gets its name.

If you want to remove all indentation from all of the line in the region, invoke C-x <TAB> with a large negative argument, such as -1000.

M-x indent-relative indents at point based on the previous line (actually, the last nonempty line). It inserts whitespace at point, moving point, until it is underneath the next indentation point in the previous line. An indentation point is the end of a sequence of whitespace or the end of the line. If point is farther right than any indentation point in the previous line, indent-relative runs tab-to-tab-stop unless it is called with a numeric argument, in which case it does nothing.

See Format Indentation, for another way of specifying the indentation for part of your text.

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29.2 Tab Stops

For typing in tables, you can use M-i (tab-to-tab-stop). This command inserts indentation before point, enough to reach the next tab stop column.

You can specify the tab stops used by M-i. They are stored in a variable called tab-stop-list, as a list of column-numbers in increasing order.

The convenient way to set the tab stops is with M-x edit-tab-stops, which creates and selects a buffer containing a description of the tab stop settings. You can edit this buffer to specify different tab stops, and then type C-c C-c to make those new tab stops take effect. The buffer uses Overwrite mode (see Minor Modes). edit-tab-stops records which buffer was current when you invoked it, and stores the tab stops back in that buffer; normally all buffers share the same tab stops and changing them in one buffer affects all, but if you happen to make tab-stop-list local in one buffer then edit-tab-stops in that buffer will edit the local settings.

Here is what the text representing the tab stops looks like for ordinary tab stops every eight columns.

             :       :       :       :       :       :
     0         1         2         3         4
     To install changes, type C-c C-c

The first line contains a colon at each tab stop. The remaining lines are present just to help you see where the colons are and know what to do.

Note that the tab stops that control tab-to-tab-stop have nothing to do with displaying tab characters in the buffer. See Display Custom, for more information on that.

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29.3 Tabs vs. Spaces

Emacs normally uses both tabs and spaces to indent lines. If you prefer, all indentation can be made from spaces only. To request this, set indent-tabs-mode to nil. This is a per-buffer variable, so altering the variable affects only the current buffer, but there is a default value which you can change as well. See Locals.

A tab is not always displayed in the same way. By default, tabs are eight columns wide, but some people like to customize their tools to use a different tab width. So by using spaces only, you can make sure that your file looks the same regardless of the tab width setting.

There are also commands to convert tabs to spaces or vice versa, always preserving the columns of all nonblank text. M-x tabify scans the region for sequences of spaces, and converts sequences of at least two spaces to tabs if that can be done without changing indentation. M-x untabify changes all tabs in the region to appropriate numbers of spaces.

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30 Commands for Human Languages

The term text has two widespread meanings in our area of the computer field. One is data that is a sequence of characters. Any file that you edit with Emacs is text, in this sense of the word. The other meaning is more restrictive: a sequence of characters in a human language for humans to read (possibly after processing by a text formatter), as opposed to a program or commands for a program.

Human languages have syntactic/stylistic conventions that can be supported or used to advantage by editor commands: conventions involving words, sentences, paragraphs, and capital letters. This chapter describes Emacs commands for all of these things. There are also commands for filling, which means rearranging the lines of a paragraph to be approximately equal in length. The commands for moving over and killing words, sentences and paragraphs, while intended primarily for editing text, are also often useful for editing programs.

Emacs has several major modes for editing human-language text. If the file contains text pure and simple, use Text mode, which customizes Emacs in small ways for the syntactic conventions of text. Outline mode provides special commands for operating on text with an outline structure.

For text which contains embedded commands for text formatters, Emacs has other major modes, each for a particular text formatter. Thus, for input to TeX, you would use TeX For input to nroff, use Nroff mode.

Instead of using a text formatter, you can edit formatted text in WYSIWYG style (“what you see is what you get”), with Enriched mode. Then the formatting appears on the screen in Emacs while you edit.

The “automatic typing” features may be useful when writing text. see Top.

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30.1 Words

Emacs has commands for moving over or operating on words. By convention, the keys for them are all Meta characters.

Move forward over a word (forward-word).
Move backward over a word (backward-word).
Kill up to the end of a word (kill-word).
Kill back to the beginning of a word (backward-kill-word).
Mark the end of the next word (mark-word).
Transpose two words or drag a word across other words (transpose-words).

Notice how these keys form a series that parallels the character-based C-f, C-b, C-d, <DEL> and C-t. M-@ is cognate to C-@, which is an alias for C-<SPC>.

The commands M-f (forward-word) and M-b (backward-word) move forward and backward over words. These Meta characters are thus analogous to the corresponding control characters, C-f and C-b, which move over single characters in the text. The analogy extends to numeric arguments, which serve as repeat counts. M-f with a negative argument moves backward, and M-b with a negative argument moves forward. Forward motion stops right after the last letter of the word, while backward motion stops right before the first letter.

M-d (kill-word) kills the word after point. To be precise, it kills everything from point to the place M-f would move to. Thus, if point is in the middle of a word, M-d kills just the part after point. If some punctuation comes between point and the next word, it is killed along with the word. (If you wish to kill only the next word but not the punctuation before it, simply do M-f to get the end, and kill the word backwards with M-<DEL>.) M-d takes arguments just like M-f.

M-<DEL> (backward-kill-word) kills the word before point. It kills everything from point back to where M-b would move to. If point is after the space in ‘FOO, BAR, then ‘FOO,  is killed. (If you wish to kill just ‘FOO’, and not the comma and the space, use M-b M-d instead of M-<DEL>.)

M-t (transpose-words) exchanges the word before or containing point with the following word. The delimiter characters between the words do not move. For example, ‘FOO, BAR transposes into ‘BAR, FOO rather than ‘BAR FOO,’. See Transpose, for more on transposition and on arguments to transposition commands.

To operate on the next n words with an operation which applies between point and mark, you can either set the mark at point and then move over the words, or you can use the command M-@ (mark-word) which does not move point, but sets the mark where M-f would move to. M-@ accepts a numeric argument that says how many words to scan for the place to put the mark. In Transient Mark mode, this command activates the mark.

The word commands' understanding of syntax is completely controlled by the syntax table. Any character can, for example, be declared to be a word delimiter. See Syntax.

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30.2 Sentences

The Emacs commands for manipulating sentences and paragraphs are mostly on Meta keys, so as to be like the word-handling commands.

Move back to the beginning of the sentence (backward-sentence).
Move forward to the end of the sentence (forward-sentence).
Kill forward to the end of the sentence (kill-sentence).
C-x <DEL>
Kill back to the beginning of the sentence (backward-kill-sentence).

The commands M-a and M-e (backward-sentence and forward-sentence) move to the beginning and end of the current sentence, respectively. They were chosen to resemble C-a and C-e, which move to the beginning and end of a line. Unlike them, M-a and M-e move over successive sentences if repeated.

Moving backward over a sentence places point just before the first character of the sentence; moving forward places point right after the punctuation that ends the sentence. Neither one moves over the whitespace at the sentence boundary.

Just as C-a and C-e have a kill command, C-k, to go with them, so M-a and M-e have a corresponding kill command M-k (kill-sentence) which kills from point to the end of the sentence. With minus one as an argument it kills back to the beginning of the sentence. Larger arguments serve as a repeat count. There is also a command, C-x <DEL> (backward-kill-sentence), for killing back to the beginning of a sentence. This command is useful when you change your mind in the middle of composing text.

The sentence commands assume that you follow the American typist's convention of putting two spaces at the end of a sentence; they consider a sentence to end wherever there is a ‘.’, ‘?’ or ‘!’ followed by the end of a line or two spaces, with any number of ‘)’, ‘]’, ‘'’, or ‘"’ characters allowed in between. A sentence also begins or ends wherever a paragraph begins or ends.

The variable sentence-end controls recognition of the end of a sentence. If non-nil, it is a regexp that matches the last few characters of a sentence, together with the whitespace following the sentence. If the value is nil, the default, then Emacs computes the regexp according to various criteria. The result is normally similar to the following regexp:

     "[.?!][]\"')]*\\($\\| $\\|\t\\|  \\)[ \t\n]*"

This example is explained in the section on regexps. See Regexp Example.

If you want to use just one space between sentences, you should set sentence-end to this value:

     "[.?!][]\"')]*\\($\\|\t\\| \\)[ \t\n]*"

This is what setting the variable sentence-end-double-space to nil automatically does. But note that this makes it impossible to distinguish between periods that end sentences and those that indicate abbreviations.

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30.3 Paragraphs

The Emacs commands for manipulating paragraphs are also Meta keys.

Move back to previous paragraph beginning (backward-paragraph).
Move forward to next paragraph end (forward-paragraph).
Put point and mark around this or next paragraph (mark-paragraph).

M-{ moves to the beginning of the current or previous paragraph, while M-} moves to the end of the current or next paragraph. Blank lines and text-formatter command lines separate paragraphs and are not considered part of any paragraph. In Paragraph-Indent Text mode, but not in Text mode, an indented line also starts a new paragraph. If there is a blank line before the paragraph, M-{ moves to the blank line, because that is convenient in practice.

In major modes for programs, paragraphs begin and end only at blank lines. This makes the paragraph commands continue to be useful even though there are no paragraphs per se.

When there is a fill prefix, then paragraphs are delimited by all lines which don't start with the fill prefix. See Filling.

When you wish to operate on a paragraph, you can use the command M-h (mark-paragraph) to set the region around it. Thus, for example, M-h C-w kills the paragraph around or after point. The M-h command puts point at the beginning and mark at the end of the paragraph point was in. In Transient Mark mode, it activates the mark. If point is between paragraphs (in a run of blank lines, or at a boundary), the paragraph following point is surrounded by point and mark. If there are blank lines preceding the first line of the paragraph, one of these blank lines is included in the region.

The precise definition of a paragraph boundary is controlled by the variables paragraph-separate and paragraph-start. The value of paragraph-start is a regexp that should match any line that either starts or separates paragraphs. The value of paragraph-separate is another regexp that should match only lines that separate paragraphs without being part of any paragraph (for example, blank lines). Lines that start a new paragraph and are contained in it must match only paragraph-start, not paragraph-separate. Each regular expression must match at the left margin. For example, in Fundamental mode, paragraph-start is "\f\\|[ \t]*$", and paragraph-separate is "[ \t\f]*$".

Normally it is desirable for page boundaries to separate paragraphs. The default values of these variables recognize the usual separator for pages.

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30.4 Pages

Files are often thought of as divided into pages by the formfeed character (ASCII control-L, octal code 014). When you print hardcopy for a file, this character forces a page break; thus, each page of the file goes on a separate page on paper. Most Emacs commands treat the page-separator character just like any other character: you can insert it with C-q C-l, and delete it with <DEL>. Thus, you are free to paginate your file or not. However, since pages are often meaningful divisions of the file, Emacs provides commands to move over them and operate on them.

C-x [
Move point to previous page boundary (backward-page).
C-x ]
Move point to next page boundary (forward-page).
C-x C-p
Put point and mark around this page (or another page) (mark-page).
C-x l
Count the lines in this page (count-lines-page).

The C-x [ (backward-page) command moves point to immediately after the previous page delimiter. If point is already right after a page delimiter, it skips that one and stops at the previous one. A numeric argument serves as a repeat count. The C-x ] (forward-page) command moves forward past the next page delimiter.

The C-x C-p command (mark-page) puts point at the beginning of the current page and the mark at the end. The page delimiter at the end is included (the mark follows it). The page delimiter at the front is excluded (point follows it). In Transient Mark mode, this command activates the mark.

C-x C-p C-w is a handy way to kill a page to move it elsewhere. If you move to another page delimiter with C-x [ and C-x ], then yank the killed page, all the pages will be properly delimited once again. The reason C-x C-p includes only the following page delimiter in the region is to ensure that.

A numeric argument to C-x C-p is used to specify which page to go to, relative to the current one. Zero means the current page. One means the next page, and −1 means the previous one.

The C-x l command (count-lines-page) is good for deciding where to break a page in two. It displays in the echo area the total number of lines in the current page, and then divides it up into those preceding the current line and those following, as in

     Page has 96 (72+25) lines

Notice that the sum is off by one; this is correct if point is not at the beginning of a line.

The variable page-delimiter controls where pages begin. Its value is a regexp that matches the beginning of a line that separates pages. The normal value of this variable is "^\f", which matches a formfeed character at the beginning of a line.

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30.5 Filling Text

Filling text means breaking it up into lines that fit a specified width. Emacs does filling in two ways. In Auto Fill mode, inserting text with self-inserting characters also automatically fills it. There are also explicit fill commands that you can use when editing text leaves it unfilled. When you edit formatted text, you can specify a style of filling for each portion of the text (see Formatted Text).

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30.5.1 Auto Fill Mode

Auto Fill mode is a minor mode in which lines are broken automatically when they become too wide. Breaking happens only when you type a <SPC> or <RET>.

M-x auto-fill-mode
Enable or disable Auto Fill mode.
In Auto Fill mode, break lines when appropriate.

M-x auto-fill-mode turns Auto Fill mode on if it was off, or off if it was on. With a positive numeric argument it always turns Auto Fill mode on, and with a negative argument always turns it off. You can see when Auto Fill mode is in effect by the presence of the word ‘Fill’ in the mode line, inside the parentheses. Auto Fill mode is a minor mode which is enabled or disabled for each buffer individually. See Minor Modes.

In Auto Fill mode, lines are broken automatically at spaces when they get longer than the desired width. Line breaking and rearrangement takes place only when you type <SPC> or <RET>. If you wish to insert a space or newline without permitting line-breaking, type C-q <SPC> or C-q C-j (recall that a newline is really a control-J). Also, C-o inserts a newline without line breaking.

Auto Fill mode works well with programming-language modes, because it indents new lines with <TAB>. If a line ending in a comment gets too long, the text of the comment is split into two comment lines. Optionally, new comment delimiters are inserted at the end of the first line and the beginning of the second so that each line is a separate comment; the variable comment-multi-line controls the choice (see Comments).

Adaptive filling (see Adaptive Fill) works for Auto Filling as well as for explicit fill commands. It takes a fill prefix automatically from the second or first line of a paragraph.

Auto Fill mode does not refill entire paragraphs; it can break lines but cannot merge lines. So editing in the middle of a paragraph can result in a paragraph that is not correctly filled. The easiest way to make the paragraph properly filled again is usually with the explicit fill commands.

Many users like Auto Fill mode and want to use it in all text files. The section on init files says how to arrange this permanently for yourself. See Init File.

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30.5.2 Refill Mode

Refill minor mode provides support for keeping paragraphs filled as you type or modify them in other ways. It provides an effect similar to typical word processor behavior. This works by running a paragraph-filling command at suitable times.

To toggle the use of Refill mode in the current buffer, type M-x refill-mode. When you are typing text, only characters which normally trigger auto filling, like the space character, will trigger refilling. This is to avoid making it too slow. Apart from self-inserting characters, other commands which modify the text cause refilling.

The current implementation is preliminary and not robust. You can get better “line wrapping” behavior using Longlines mode. See Longlines. However, Longlines mode has an important side-effect: the newlines that it inserts for you are not saved to disk, so the files that you make with Longlines mode will appear to be completely unfilled if you edit them without Longlines mode.

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30.5.3 Explicit Fill Commands

Fill current paragraph (fill-paragraph).
C-x f
Set the fill column (set-fill-column).
M-x fill-region
Fill each paragraph in the region (fill-region).
M-x fill-region-as-paragraph
Fill the region, considering it as one paragraph.
Center a line.

To refill a paragraph, use the command M-q (fill-paragraph). This operates on the paragraph that point is inside, or the one after point if point is between paragraphs. Refilling works by removing all the line-breaks, then inserting new ones where necessary.

To refill many paragraphs, use M-x fill-region, which divides the region into paragraphs and fills each of them.

M-q and fill-region use the same criteria as M-h for finding paragraph boundaries (see Paragraphs). For more control, you can use M-x fill-region-as-paragraph, which refills everything between point and mark. This command deletes any blank lines within the region, so separate blocks of text end up combined into one block.

A numeric argument to M-q causes it to justify the text as well as filling it. This means that extra spaces are inserted to make the right margin line up exactly at the fill column. To remove the extra spaces, use M-q with no argument. (Likewise for fill-region.) Another way to control justification, and choose other styles of filling, is with the justification text property; see Format Justification.

The command M-s (center-line) centers the current line within the current fill column. With an argument n, it centers n lines individually and moves past them. This binding is made by Text mode and is available only in that and related modes (see Text Mode).

The maximum line width for filling is in the variable fill-column. Altering the value of fill-column makes it local to the current buffer; until that time, the default value is in effect. The default is initially 70. See Locals. The easiest way to set fill-column is to use the command C-x f (set-fill-column). With a numeric argument, it uses that as the new fill column. With just C-u as argument, it sets fill-column to the current horizontal position of point.

Emacs commands normally consider a period followed by two spaces or by a newline as the end of a sentence; a period followed by just one space indicates an abbreviation and not the end of a sentence. To preserve the distinction between these two ways of using a period, the fill commands do not break a line after a period followed by just one space.

If the variable sentence-end-double-space is nil, the fill commands expect and leave just one space at the end of a sentence. Ordinarily this variable is t, so the fill commands insist on two spaces for the end of a sentence, as explained above. See Sentences.

If the variable colon-double-space is non-nil, the fill commands put two spaces after a colon.

Some languages do not use period to indicate end of sentence. For example, a sentence in Thai text ends with double space but without a period. Set the variable sentence-end-without-period to t to tell the sentence commands that a period is not necessary.

The variable fill-nobreak-predicate specifies additional conditions for where line-breaking is allowed. Its value is either nil or a Lisp function; the function is called with no arguments, and if it returns a non-nil value, then point is not a good place to break the line. Two standard functions you can use are fill-single-word-nobreak-p (don't break after the first word of a sentence or before the last) and fill-french-nobreak-p (don't break after ‘(’ or before ‘)’, ‘:’ or ‘?’).

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30.5.4 The Fill Prefix

To fill a paragraph in which each line starts with a special marker (which might be a few spaces, giving an indented paragraph), you can use the fill prefix feature. The fill prefix is a string that Emacs expects every line to start with, and which is not included in filling. You can specify a fill prefix explicitly; Emacs can also deduce the fill prefix automatically (see Adaptive Fill).

C-x .
Set the fill prefix (set-fill-prefix).
Fill a paragraph using current fill prefix (fill-paragraph).
M-x fill-individual-paragraphs
Fill the region, considering each change of indentation as starting a new paragraph.
M-x fill-nonuniform-paragraphs
Fill the region, considering only paragraph-separator lines as starting a new paragraph.

To specify a fill prefix for the current buffer, move to a line that starts with the desired prefix, put point at the end of the prefix, and give the command C-x . (set-fill-prefix). That's a period after the C-x. To turn off the fill prefix, specify an empty prefix: type C-x . with point at the beginning of a line.

When a fill prefix is in effect, the fill commands remove the fill prefix from each line before filling and insert it on each line after filling. (The beginning of the first line is left unchanged, since often that is intentionally different.) Auto Fill mode also inserts the fill prefix automatically when it makes a new line. The C-o command inserts the fill prefix on new lines it creates, when you use it at the beginning of a line (see Blank Lines). Conversely, the command M-^ deletes the prefix (if it occurs) after the newline that it deletes (see Indentation).

For example, if fill-column is 40 and you set the fill prefix to ‘;; ’, then M-q in the following text

     ;; This is an
     ;; example of a paragraph
     ;; inside a Lisp-style comment.

produces this:

     ;; This is an example of a paragraph
     ;; inside a Lisp-style comment.

Lines that do not start with the fill prefix are considered to start paragraphs, both in M-q and the paragraph commands; this gives good results for paragraphs with hanging indentation (every line indented except the first one). Lines which are blank or indented once the prefix is removed also separate or start paragraphs; this is what you want if you are writing multi-paragraph comments with a comment delimiter on each line.

You can use M-x fill-individual-paragraphs to set the fill prefix for each paragraph automatically. This command divides the region into paragraphs, treating every change in the amount of indentation as the start of a new paragraph, and fills each of these paragraphs. Thus, all the lines in one “paragraph” have the same amount of indentation. That indentation serves as the fill prefix for that paragraph.

M-x fill-nonuniform-paragraphs is a similar command that divides the region into paragraphs in a different way. It considers only paragraph-separating lines (as defined by paragraph-separate) as starting a new paragraph. Since this means that the lines of one paragraph may have different amounts of indentation, the fill prefix used is the smallest amount of indentation of any of the lines of the paragraph. This gives good results with styles that indent a paragraph's first line more or less that the rest of the paragraph.

The fill prefix is stored in the variable fill-prefix. Its value is a string, or nil when there is no fill prefix. This is a per-buffer variable; altering the variable affects only the current buffer, but there is a default value which you can change as well. See Locals.

The indentation text property provides another way to control the amount of indentation paragraphs receive. See Format Indentation.

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30.5.5 Adaptive Filling

The fill commands can deduce the proper fill prefix for a paragraph automatically in certain cases: either whitespace or certain punctuation characters at the beginning of a line are propagated to all lines of the paragraph.

If the paragraph has two or more lines, the fill prefix is taken from the paragraph's second line, but only if it appears on the first line as well.

If a paragraph has just one line, fill commands may take a prefix from that line. The decision is complicated because there are three reasonable things to do in such a case:

All three of these styles of formatting are commonly used. So the fill commands try to determine what you would like, based on the prefix that appears and on the major mode. Here is how.

If the prefix found on the first line matches adaptive-fill-first-line-regexp, or if it appears to be a comment-starting sequence (this depends on the major mode), then the prefix found is used for filling the paragraph, provided it would not act as a paragraph starter on subsequent lines.

Otherwise, the prefix found is converted to an equivalent number of spaces, and those spaces are used as the fill prefix for the rest of the lines, provided they would not act as a paragraph starter on subsequent lines.

In Text mode, and other modes where only blank lines and page delimiters separate paragraphs, the prefix chosen by adaptive filling never acts as a paragraph starter, so it can always be used for filling.

The variable adaptive-fill-regexp determines what kinds of line beginnings can serve as a fill prefix: any characters at the start of the line that match this regular expression are used. If you set the variable adaptive-fill-mode to nil, the fill prefix is never chosen automatically.

You can specify more complex ways of choosing a fill prefix automatically by setting the variable adaptive-fill-function to a function. This function is called with point after the left margin of a line, and it should return the appropriate fill prefix based on that line. If it returns nil, adaptive-fill-regexp gets a chance to find a prefix.

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30.5.6 Long Lines Mode

Long Lines mode is a minor mode for word wrapping; it lets you edit “unfilled” text files, which Emacs would normally display as a bunch of extremely long lines. Many text editors, such as those built into many web browsers, normally do word wrapping.

To enable Long Lines mode, type M-x longlines-mode. If the text is full of long lines, this will “wrap” them immediately—i.e., break up to fit in the window. As you edit the text, Long Lines mode automatically re-wraps lines by inserting or deleting soft newlines as necessary (see Hard and Soft Newlines.) These soft newlines won't show up when you save the buffer into a file, or when you copy the text into the kill ring, clipboard, or a register.

Word wrapping is not the same as ordinary filling (see Fill Commands). It does not contract multiple spaces into a single space, recognize fill prefixes (see Fill Prefix), or perform adaptive filling (see Adaptive Fill). The reason for this is that a wrapped line is still, conceptually, a single line. Each soft newline is equivalent to exactly one space in that long line, and vice versa. However, you can still call filling functions such as M-q, and these will work as expected, inserting soft newlines that won't show up on disk or when the text is copied. You can even rely entirely on the normal fill commands by turning off automatic line wrapping, with C-u M-x longlines-auto-wrap. To turn automatic line wrapping back on, type M-x longlines-auto-wrap.

Whenever you type RET, you are inserting a hard newline. If you want to see where all the hard newlines are, type M-x longlines-show-hard-newlines. This will mark each hard newline with a special symbol. The same command with a prefix argument turns this display off.

Long Lines mode does not change normal text files that are already filled, since the existing newlines are considered hard newlines. Before Long Lines can do anything, you need to transform each paragraph into a long line. One way is to set fill-column to a large number (e.g., C-u 9999 C-x f), re-fill all the paragraphs, and then set fill-column back to its original value.

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30.6 Case Conversion Commands

Emacs has commands for converting either a single word or any arbitrary range of text to upper case or to lower case.

Convert following word to lower case (downcase-word).
Convert following word to upper case (upcase-word).
Capitalize the following word (capitalize-word).
C-x C-l
Convert region to lower case (downcase-region).
C-x C-u
Convert region to upper case (upcase-region).

The word conversion commands are the most useful. M-l (downcase-word) converts the word after point to lower case, moving past it. Thus, repeating M-l converts successive words. M-u (upcase-word) converts to all capitals instead, while M-c (capitalize-word) puts the first letter of the word into upper case and the rest into lower case. All these commands convert several words at once if given an argument. They are especially convenient for converting a large amount of text from all upper case to mixed case, because you can move through the text using M-l, M-u or M-c on each word as appropriate, occasionally using M-f instead to skip a word.

When given a negative argument, the word case conversion commands apply to the appropriate number of words before point, but do not move point. This is convenient when you have just typed a word in the wrong case: you can give the case conversion command and continue typing.

If a word case conversion command is given in the middle of a word, it applies only to the part of the word which follows point. This is just like what M-d (kill-word) does. With a negative argument, case conversion applies only to the part of the word before point.

The other case conversion commands are C-x C-u (upcase-region) and C-x C-l (downcase-region), which convert everything between point and mark to the specified case. Point and mark do not move.

The region case conversion commands upcase-region and downcase-region are normally disabled. This means that they ask for confirmation if you try to use them. When you confirm, you may enable the command, which means it will not ask for confirmation again. See Disabling.

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30.7 Text Mode

When you edit files of text in a human language, it's more convenient to use Text mode rather than Fundamental mode. To enter Text mode, type M-x text-mode.

In Text mode, only blank lines and page delimiters separate paragraphs. As a result, paragraphs can be indented, and adaptive filling determines what indentation to use when filling a paragraph. See Adaptive Fill.

Text mode defines <TAB> to run indent-relative (see Indentation), so that you can conveniently indent a line like the previous line.

Text mode turns off the features concerned with comments except when you explicitly invoke them. It changes the syntax table so that single-quotes are considered part of words. However, if a word starts with single-quotes, then these are treated as a prefix for purposes such as capitalization. That is, M-c will convert ‘'hello'’ into ‘'Hello'’, as expected.

If you indent the first lines of paragraphs, then you should use Paragraph-Indent Text mode rather than Text mode. In this mode, you do not need to have blank lines between paragraphs, because the first-line indentation is sufficient to start a paragraph; however paragraphs in which every line is indented are not supported. Use M-x paragraph-indent-text-mode to enter this mode. Use M-x paragraph-indent-minor-mode to enter an equivalent minor mode, for instance during mail composition.

Text mode, and all the modes based on it, define M-<TAB> as the command ispell-complete-word, which performs completion of the partial word in the buffer before point, using the spelling dictionary as the space of possible words. See Spelling. If your window manager defines M-<TAB> to switch windows, you can type <ESC> <TAB> or C-M-i.

Entering Text mode runs the hook text-mode-hook. Other major modes related to Text mode also run this hook, followed by hooks of their own; this includes Paragraph-Indent Text mode, Nroff mode, TeX mode, Outline mode, and Mail mode. Hook functions on text-mode-hook can look at the value of major-mode to see which of these modes is actually being entered. See Hooks.

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30.8 Outline Mode

Outline mode is a major mode much like Text mode but intended for editing outlines. It allows you to make parts of the text temporarily invisible so that you can see the outline structure. Type M-x outline-mode to switch to Outline mode as the major mode of the current buffer.

When Outline mode makes a line invisible, the line does not appear on the screen. The screen appears exactly as if the invisible line were deleted, except that an ellipsis (three periods in a row) appears at the end of the previous visible line. (Multiple consecutive invisible lines produce just one ellipsis.)

Editing commands that operate on lines, such as C-n and C-p, treat the text of the invisible line as part of the previous visible line. Killing the ellipsis at the end of a visible line really kills all the following invisible lines.

Outline minor mode provides the same commands as the major mode, Outline mode, but you can use it in conjunction with other major modes. Type M-x outline-minor-mode to enable the Outline minor mode in the current buffer. You can also specify this in the text of a file, with a file local variable of the form ‘mode: outline-minor’ (see File Variables).

The major mode, Outline mode, provides special key bindings on the C-c prefix. Outline minor mode provides similar bindings with C-c @ as the prefix; this is to reduce the conflicts with the major mode's special commands. (The variable outline-minor-mode-prefix controls the prefix used.)

Entering Outline mode runs the hook text-mode-hook followed by the hook outline-mode-hook (see Hooks).

Next: , Up: Outline Mode

30.8.1 Format of Outlines

Outline mode assumes that the lines in the buffer are of two types: heading lines and body lines. A heading line represents a topic in the outline. Heading lines start with one or more stars; the number of stars determines the depth of the heading in the outline structure. Thus, a heading line with one star is a major topic; all the heading lines with two stars between it and the next one-star heading are its subtopics; and so on. Any line that is not a heading line is a body line. Body lines belong with the preceding heading line. Here is an example:

     * Food
     This is the body,
     which says something about the topic of food.
     ** Delicious Food
     This is the body of the second-level header.
     ** Distasteful Food
     This could have
     a body too, with
     several lines.
     *** Dormitory Food
     * Shelter
     Another first-level topic with its header line.

A heading line together with all following body lines is called collectively an entry. A heading line together with all following deeper heading lines and their body lines is called a subtree.

You can customize the criterion for distinguishing heading lines by setting the variable outline-regexp. Any line whose beginning has a match for this regexp is considered a heading line. Matches that start within a line (not at the left margin) do not count. The length of the matching text determines the level of the heading; longer matches make a more deeply nested level. Thus, for example, if a text formatter has commands ‘@chapter’, ‘@section’ and ‘@subsection’ to divide the document into chapters and sections, you could make those lines count as heading lines by setting outline-regexp to ‘"@chap\\|@\\(sub\\)*section"’. Note the trick: the two words ‘chapter’ and ‘section’ are equally long, but by defining the regexp to match only ‘chap’ we ensure that the length of the text matched on a chapter heading is shorter, so that Outline mode will know that sections are contained in chapters. This works as long as no other command starts with ‘@chap’.

You can change the rule for calculating the level of a heading line by setting the variable outline-level. The value of outline-level should be a function that takes no arguments and returns the level of the current heading. Some major modes such as C, Nroff, and Emacs Lisp mode set this variable and outline-regexp in order to work with Outline minor mode.

Next: , Previous: Outline Format, Up: Outline Mode

30.8.2 Outline Motion Commands

Outline mode provides special motion commands that move backward and forward to heading lines.

C-c C-n
Move point to the next visible heading line (outline-next-visible-heading).
C-c C-p
Move point to the previous visible heading line (outline-previous-visible-heading).
C-c C-f
Move point to the next visible heading line at the same level as the one point is on (outline-forward-same-level).
C-c C-b
Move point to the previous visible heading line at the same level (outline-backward-same-level).
C-c C-u
Move point up to a lower-level (more inclusive) visible heading line (outline-up-heading).

C-c C-n (outline-next-visible-heading) moves down to the next heading line. C-c C-p (outline-previous-visible-heading) moves similarly backward. Both accept numeric arguments as repeat counts. The names emphasize that invisible headings are skipped, but this is not really a special feature. All editing commands that look for lines ignore the invisible lines automatically.

More powerful motion commands understand the level structure of headings. C-c C-f (outline-forward-same-level) and C-c C-b (outline-backward-same-level) move from one heading line to another visible heading at the same depth in the outline. C-c C-u (outline-up-heading) moves backward to another heading that is less deeply nested.

Next: , Previous: Outline Motion, Up: Outline Mode

30.8.3 Outline Visibility Commands

The other special commands of outline mode are used to make lines visible or invisible. Their names all start with hide or show. Most of them fall into pairs of opposites. They are not undoable; instead, you can undo right past them. Making lines visible or invisible is simply not recorded by the undo mechanism.

Many of these commands act on the “current” heading line. If point is on a heading line, that is the current heading line; if point is on a body line, the current heading line is the nearest preceding header line.

C-c C-c
Make the current heading line's body invisible (hide-entry).
C-c C-e
Make the current heading line's body visible (show-entry).
C-c C-d
Make everything under the current heading invisible, not including the heading itself (hide-subtree).
C-c C-s
Make everything under the current heading visible, including body, subheadings, and their bodies (show-subtree).
C-c C-l
Make the body of the current heading line, and of all its subheadings, invisible (hide-leaves).
C-c C-k
Make all subheadings of the current heading line, at all levels, visible (show-branches).
C-c C-i
Make immediate subheadings (one level down) of the current heading line visible (show-children).
C-c C-t
Make all body lines in the buffer invisible (hide-body).
C-c C-a
Make all lines in the buffer visible (show-all).
C-c C-q
Hide everything except the top n levels of heading lines (hide-sublevels).
C-c C-o
Hide everything except for the heading or body that point is in, plus the headings leading up from there to the top level of the outline (hide-other).

Two commands that are exact opposites are C-c C-c (hide-entry) and C-c C-e (show-entry). They apply to the body lines directly following the current heading line. Subheadings and their bodies are not affected.

Two more powerful opposites are C-c C-d (hide-subtree) and C-c C-s (show-subtree). Both apply to the current heading line's subtree: its body, all its subheadings, both direct and indirect, and all of their bodies. In other words, the subtree contains everything following the current heading line, up to and not including the next heading of the same or higher rank.

Intermediate between a visible subtree and an invisible one is having all the subheadings visible but none of the body. There are two commands for doing this, depending on whether you want to hide the bodies or make the subheadings visible. They are C-c C-l (hide-leaves) and C-c C-k (show-branches).

A little weaker than show-branches is C-c C-i (show-children). It makes just the direct subheadings visible—those one level down. Deeper subheadings remain invisible, if they were invisible.

Two commands have a blanket effect on the whole file. C-c C-t (hide-body) makes all body lines invisible, so that you see just the outline structure (as a special exception, it will not hide lines at the top of the file, preceding the first header line, even though these are technically body lines). C-c C-a (show-all) makes all lines visible. These commands can be thought of as a pair of opposites even though C-c C-a applies to more than just body lines.

The command C-c C-q (hide-sublevels) hides all but the top level headings. With a numeric argument n, it hides everything except the top n levels of heading lines.

The command C-c C-o (hide-other) hides everything except the heading and body text that point is in, plus its parents (the headers leading up from there to top level in the outline) and the top level headings.

When incremental search finds text that is hidden by Outline mode, it makes that part of the buffer visible. If you exit the search at that position, the text remains visible. You can also automatically make text visible as you navigate in it by using M-x reveal-mode.

Next: , Previous: Outline Visibility, Up: Outline Mode

30.8.4 Viewing One Outline in Multiple Views

You can display two views of a single outline at the same time, in different windows. To do this, you must create an indirect buffer using M-x make-indirect-buffer. The first argument of this command is the existing outline buffer name, and its second argument is the name to use for the new indirect buffer. See Indirect Buffers.

Once the indirect buffer exists, you can display it in a window in the normal fashion, with C-x 4 b or other Emacs commands. The Outline mode commands to show and hide parts of the text operate on each buffer independently; as a result, each buffer can have its own view. If you want more than two views on the same outline, create additional indirect buffers.

Previous: Outline Views, Up: Outline Mode

30.8.5 Folding Editing

The Foldout package extends Outline mode and Outline minor mode with “folding” commands. The idea of folding is that you zoom in on a nested portion of the outline, while hiding its relatives at higher levels.

Consider an Outline mode buffer with all the text and subheadings under level-1 headings hidden. To look at what is hidden under one of these headings, you could use C-c C-e (M-x show-entry) to expose the body, or C-c C-i to expose the child (level-2) headings.

With Foldout, you use C-c C-z (M-x foldout-zoom-subtree). This exposes the body and child subheadings, and narrows the buffer so that only the level-1 heading, the body and the level-2 headings are visible. Now to look under one of the level-2 headings, position the cursor on it and use C-c C-z again. This exposes the level-2 body and its level-3 child subheadings and narrows the buffer again. Zooming in on successive subheadings can be done as much as you like. A string in the mode line shows how deep you've gone.

When zooming in on a heading, to see only the child subheadings specify a numeric argument: C-u C-c C-z. The number of levels of children can be specified too (compare M-x show-children), e.g. M-2 C-c C-z exposes two levels of child subheadings. Alternatively, the body can be specified with a negative argument: M-- C-c C-z. The whole subtree can be expanded, similarly to C-c C-s (M-x show-subtree), by specifying a zero argument: M-0 C-c C-z.

While you're zoomed in, you can still use Outline mode's exposure and hiding functions without disturbing Foldout. Also, since the buffer is narrowed, “global” editing actions will only affect text under the zoomed-in heading. This is useful for restricting changes to a particular chapter or section of your document.

To unzoom (exit) a fold, use C-c C-x (M-x foldout-exit-fold). This hides all the text and subheadings under the top-level heading and returns you to the previous view of the buffer. Specifying a numeric argument exits that many levels of folds. Specifying a zero argument exits all folds.

To cancel the narrowing of a fold without hiding the text and subheadings, specify a negative argument. For example, M--2 C-c C-x exits two folds and leaves the text and subheadings exposed.

Foldout mode also provides mouse commands for entering and exiting folds, and for showing and hiding text:

C-M-Mouse-1 zooms in on the heading clicked on

C-M-Mouse-2 exposes text under the heading clicked on

C-M-Mouse-3 hides text under the heading clicked on or exits fold

You can specify different modifier keys (instead of Control-Meta-) by setting foldout-mouse-modifiers; but if you have already loaded the foldout.el library, you must reload it in order for this to take effect.

To use the Foldout package, you can type M-x load-library <RET> foldout <RET>; or you can arrange for to do that automatically by putting this in your .emacs file:

     (eval-after-load "outline" '(require 'foldout))

Next: , Previous: Outline Mode, Up: Text

30.9 TeX Mode

TeX is a powerful text formatter written by Donald Knuth; it is also free, like GNU Emacs. LaTeX is a simplified input format for TeX, implemented by TeX macros; it comes with TeX. SliTeX is a special form of LaTeX.11 DocTeX (.dtx) is a special file format in which the LaTeX sources are written, combining sources with documentation.

Emacs has a special TeX mode for editing TeX input files. It provides facilities for checking the balance of delimiters and for invoking TeX on all or part of the file.

TeX mode has four variants: Plain TeX mode, LaTeX mode, SliTeX mode, and DocTeX mode (these distinct major modes differ only slightly). They are designed for editing the four different formats. The command M-x tex-mode looks at the contents of the buffer to determine whether the contents appear to be either LaTeX input, SliTeX, or DocTeX input; if so, it selects the appropriate mode. If the file contents do not appear to be LaTeX, SliTeX or DocTeX, it selects Plain TeX mode. If the contents are insufficient to determine this, the variable tex-default-mode controls which mode is used.

When M-x tex-mode does not guess right, you can use the commands M-x plain-tex-mode, M-x latex-mode, M-x slitex-mode, and doctex-mode to select explicitly the particular variants of TeX mode.

Next: , Up: TeX Mode

30.9.1 TeX Editing Commands

Here are the special commands provided in TeX mode for editing the text of the file.

Insert, according to context, either ‘``’ or ‘"’ or ‘''’ (tex-insert-quote).
Insert a paragraph break (two newlines) and check the previous paragraph for unbalanced braces or dollar signs (tex-terminate-paragraph).
M-x tex-validate-region
Check each paragraph in the region for unbalanced braces or dollar signs.
C-c {
Insert ‘{}’ and position point between them (tex-insert-braces).
C-c }
Move forward past the next unmatched close brace (up-list).

In TeX, the character ‘"’ is not normally used; we use ‘``’ to start a quotation and ‘''’ to end one. To make editing easier under this formatting convention, TeX mode overrides the normal meaning of the key " with a command that inserts a pair of single-quotes or backquotes (tex-insert-quote). To be precise, this command inserts ‘``’ after whitespace or an open brace, ‘"’ after a backslash, and ‘''’ after any other character.

If you need the character ‘"’ itself in unusual contexts, use C-q to insert it. Also, " with a numeric argument always inserts that number of ‘"’ characters. You can turn off the feature of " expansion by eliminating that binding in the local map (see Key Bindings).

In TeX mode, ‘$’ has a special syntax code which attempts to understand the way TeX math mode delimiters match. When you insert a ‘$’ that is meant to exit math mode, the position of the matching ‘$’ that entered math mode is displayed for a second. This is the same feature that displays the open brace that matches a close brace that is inserted. However, there is no way to tell whether a ‘$’ enters math mode or leaves it; so when you insert a ‘$’ that enters math mode, the previous ‘$’ position is shown as if it were a match, even though they are actually unrelated.

TeX uses braces as delimiters that must match. Some users prefer to keep braces balanced at all times, rather than inserting them singly. Use C-c { (tex-insert-braces) to insert a pair of braces. It leaves point between the two braces so you can insert the text that belongs inside. Afterward, use the command C-c } (up-list) to move forward past the close brace.

There are two commands for checking the matching of braces. C-j (tex-terminate-paragraph) checks the paragraph before point, and inserts two newlines to start a new paragraph. It outputs a message in the echo area if any mismatch is found. M-x tex-validate-region checks a region, paragraph by paragraph. The errors are listed in the ‘*Occur*’ buffer, and you can use C-c C-c or Mouse-2 in that buffer to go to a particular mismatch.

Note that Emacs commands count square brackets and parentheses in TeX mode, not just braces. This is not strictly correct for the purpose of checking TeX syntax. However, parentheses and square brackets are likely to be used in text as matching delimiters and it is useful for the various motion commands and automatic match display to work with them.

Next: , Previous: TeX Editing, Up: TeX Mode

30.9.2 LaTeX Editing Commands

LaTeX mode, and its variant, SliTeX mode, provide a few extra features not applicable to plain TeX.

C-c C-o
Insert ‘\begin’ and ‘\end’ for LaTeX block and position point on a line between them (tex-latex-block).
C-c C-e
Close the innermost LaTeX block not yet closed (tex-close-latex-block).

In LaTeX input, ‘\begin’ and ‘\end’ commands are used to group blocks of text. To insert a ‘\begin’ and a matching ‘\end’ (on a new line following the ‘\begin’), use C-c C-o (tex-latex-block). A blank line is inserted between the two, and point is left there. You can use completion when you enter the block type; to specify additional block type names beyond the standard list, set the variable latex-block-names. For example, here's how to add ‘theorem’, ‘corollary’, and ‘proof’:

     (setq latex-block-names '("theorem" "corollary" "proof"))

In LaTeX input, ‘\begin’ and ‘\end’ commands must balance. You can use C-c C-e (tex-close-latex-block) to insert automatically a matching ‘\end’ to match the last unmatched ‘\begin’. It indents the ‘\end’ to match the corresponding ‘\begin’. It inserts a newline after ‘\end’ if point is at the beginning of a line.

Next: , Previous: LaTeX Editing, Up: TeX Mode

30.9.3 TeX Printing Commands

You can invoke TeX as an inferior of Emacs on either the entire contents of the buffer or just a region at a time. Running TeX in this way on just one chapter is a good way to see what your changes look like without taking the time to format the entire file.

C-c C-r
Invoke TeX on the current region, together with the buffer's header (tex-region).
C-c C-b
Invoke TeX on the entire current buffer (tex-buffer).
C-c <TAB>
Invoke BibTeX on the current file (tex-bibtex-file).
C-c C-f
Invoke TeX on the current file (tex-file).
C-c C-l
Recenter the window showing output from the inferior TeX so that the last line can be seen (tex-recenter-output-buffer).
C-c C-k
Kill the TeX subprocess (tex-kill-job).
C-c C-p
Print the output from the last C-c C-r, C-c C-b, or C-c C-f command (tex-print).
C-c C-v
Preview the output from the last C-c C-r, C-c C-b, or C-c C-f command (tex-view).
C-c C-q
Show the printer queue (tex-show-print-queue).
C-c C-c
Invoke some other compilation command on the entire current buffer (tex-compile).

You can pass the current buffer through an inferior TeX by means of C-c C-b (tex-buffer). The formatted output appears in a temporary file; to print it, type C-c C-p (tex-print). Afterward, you can use C-c C-q (tex-show-print-queue) to view the progress of your output towards being printed. If your terminal has the ability to display TeX output files, you can preview the output on the terminal with C-c C-v (tex-view).

You can specify the directory to use for running TeX by setting the variable tex-directory. "." is the default value. If your environment variable TEXINPUTS contains relative directory names, or if your files contains ‘\input’ commands with relative file names, then tex-directory must be "." or you will get the wrong results. Otherwise, it is safe to specify some other directory, such as "/tmp".

If you want to specify which shell commands are used in the inferior TeX, you can do so by setting the values of the variables tex-run-command, latex-run-command, slitex-run-command, tex-dvi-print-command, tex-dvi-view-command, and tex-show-queue-command. You must set the value of tex-dvi-view-command for your particular terminal; this variable has no default value. The other variables have default values that may (or may not) be appropriate for your system.

Normally, the file name given to these commands comes at the end of the command string; for example, ‘latex filename’. In some cases, however, the file name needs to be embedded in the command; an example is when you need to provide the file name as an argument to one command whose output is piped to another. You can specify where to put the file name with ‘*’ in the command string. For example,

     (setq tex-dvi-print-command "dvips -f * | lpr")

The terminal output from TeX, including any error messages, appears in a buffer called ‘*tex-shell*’. If TeX gets an error, you can switch to this buffer and feed it input (this works as in Shell mode; see Interactive Shell). Without switching to this buffer you can scroll it so that its last line is visible by typing C-c C-l.

Type C-c C-k (tex-kill-job) to kill the TeX process if you see that its output is no longer useful. Using C-c C-b or C-c C-r also kills any TeX process still running.

You can also pass an arbitrary region through an inferior TeX by typing C-c C-r (tex-region). This is tricky, however, because most files of TeX input contain commands at the beginning to set parameters and define macros, without which no later part of the file will format correctly. To solve this problem, C-c C-r allows you to designate a part of the file as containing essential commands; it is included before the specified region as part of the input to TeX. The designated part of the file is called the header.

To indicate the bounds of the header in Plain TeX mode, you insert two special strings in the file. Insert ‘%**start of header’ before the header, and ‘%**end of header’ after it. Each string must appear entirely on one line, but there may be other text on the line before or after. The lines containing the two strings are included in the header. If ‘%**start of header’ does not appear within the first 100 lines of the buffer, C-c C-r assumes that there is no header.

In LaTeX mode, the header begins with ‘\documentclass’ or ‘\documentstyle’ and ends with ‘\begin{document}’. These are commands that LaTeX requires you to use in any case, so nothing special needs to be done to identify the header.

The commands (tex-buffer) and (tex-region) do all of their work in a temporary directory, and do not have available any of the auxiliary files needed by TeX for cross-references; these commands are generally not suitable for running the final copy in which all of the cross-references need to be correct.

When you want the auxiliary files for cross references, use C-c C-f (tex-file) which runs TeX on the current buffer's file, in that file's directory. Before running TeX, it offers to save any modified buffers. Generally, you need to use (tex-file) twice to get the cross-references right.

The value of the variable tex-start-options specifies options for the TeX run.

The value of the variable tex-start-commands specifies TeX commands for starting TeX. The default value causes TeX to run in nonstop mode. To run TeX interactively, set the variable to "".

Large TeX documents are often split into several files—one main file, plus subfiles. Running TeX on a subfile typically does not work; you have to run it on the main file. In order to make tex-file useful when you are editing a subfile, you can set the variable tex-main-file to the name of the main file. Then tex-file runs TeX on that file.

The most convenient way to use tex-main-file is to specify it in a local variable list in each of the subfiles. See File Variables.

For LaTeX files, you can use BibTeX to process the auxiliary file for the current buffer's file. BibTeX looks up bibliographic citations in a data base and prepares the cited references for the bibliography section. The command C-c TAB (tex-bibtex-file) runs the shell command (tex-bibtex-command) to produce a ‘.bbl’ file for the current buffer's file. Generally, you need to do C-c C-f (tex-file) once to generate the ‘.aux’ file, then do C-c TAB (tex-bibtex-file), and then repeat C-c C-f (tex-file) twice more to get the cross-references correct.

To invoke some other compilation program on the current TeX buffer, type C-c C-c (tex-compile). This command knows how to pass arguments to many common programs, including pdflatex, yap, xdvi, and dvips. You can select your desired compilation program using the standard completion keys (see Completion).

Previous: TeX Print, Up: TeX Mode

30.9.4 TeX Mode Miscellany

Entering any variant of TeX mode runs the hooks text-mode-hook and tex-mode-hook. Then it runs either plain-tex-mode-hook, latex-mode-hook, or slitex-mode-hook, whichever is appropriate. Starting the TeX shell runs the hook tex-shell-hook. See Hooks.

The commands M-x iso-iso2tex, M-x iso-tex2iso, M-x iso-iso2gtex and M-x iso-gtex2iso can be used to convert between Latin-1 encoded files and TeX-encoded equivalents.

For managing all kinds of references for LaTeX, you can use RefTeX. see Top.

Next: , Previous: TeX Mode, Up: Text

30.10 SGML, XML, and HTML Modes

The major modes for SGML and HTML include indentation support and commands to operate on tags. This section describes the special commands of these modes. (HTML mode is a slightly customized variant of SGML mode.)

C-c C-n
Interactively specify a special character and insert the SGML ‘&’-command for that character.
C-c C-t
Interactively specify a tag and its attributes (sgml-tag). This command asks you for a tag name and for the attribute values, then inserts both the opening tag and the closing tag, leaving point between them.

With a prefix argument n, the command puts the tag around the n words already present in the buffer after point. With −1 as argument, it puts the tag around the region. (In Transient Mark mode, it does this whenever a region is active.)

C-c C-a
Interactively insert attribute values for the current tag (sgml-attributes).
C-c C-f
Skip across a balanced tag group (which extends from an opening tag through its corresponding closing tag) (sgml-skip-tag-forward). A numeric argument acts as a repeat count.
C-c C-b
Skip backward across a balanced tag group (which extends from an opening tag through its corresponding closing tag) (sgml-skip-tag-forward). A numeric argument acts as a repeat count.