GNU Libidn (idn) – Internationalized Domain Names command line tool
idn allows internationalized string preparation
(`stringprep'), encoding and decoding of punycode data, and IDNA
ToASCII/ToUnicode operations to be performed on the command line.
If strings are specified on the command line, they are used as input
and the computed output is printed to standard output stdout.
If no strings are specified on the command line, the program read
data, line by line, from the standard input stdin, and print
the computed output to standard output. What processing is performed
(e.g., ToASCII, or Punycode encode) is indicated by options. If any
errors are encountered, the execution of the applications is aborted.
All strings are expected to be encoded in the preferred charset used
by your locale. Use --debug to find out what this charset is.
You can override the charset used by setting environment variable
CHARSET.
To process a string that starts with -, for example
-foo, use -- to signal the end of parameters, as in
idn --quiet -a -- -foo.
idn recognizes these commands:
-h, --help Print help and exit
-V, --version Print version and exit
-s, --stringprep Prepare string according to nameprep profile
-d, --punycode-decode Decode Punycode
-e, --punycode-encode Encode Punycode
-a, --idna-to-ascii Convert to ACE according to IDNA (default)
-u, --idna-to-unicode Convert from ACE according to IDNA
--allow-unassigned Toggle IDNA AllowUnassigned flag (default=off)
--usestd3asciirules Toggle IDNA UseSTD3ASCIIRules flag (default=off)
-t, --tld Check string for TLD specific rules
Only for --idna-to-ascii and --idna-to-unicode
(default=on)
-p, --profile=STRING Use specified stringprep profile instead
Valid stringprep profiles are `Nameprep',
`iSCSI', `Nodeprep', `Resourceprep', `trace', and
`SASLprep'.
--debug Print debugging information (default=off)
--quiet Silent operation (default=off)
The CHARSET environment variable can be used to override what character set to be used for decoding incoming data (i.e., on the command line or on the standard input stream), and to encode data to the standard output. If your system is set up correctly, however, the application will guess which character set is used automatically. Example usage:
$ CHARSET=ISO-8859-1 idn --punycode-encode
...
Standard usage, reading input from standard input:
jas@latte:~$ idn
libidn 0.3.5
Copyright 2002, 2003 Simon Josefsson.
GNU Libidn comes with NO WARRANTY, to the extent permitted by law.
You may redistribute copies of GNU Libidn under the terms of
the GNU Lesser General Public License. For more information
about these matters, see the file named COPYING.LIB.
Type each input string on a line by itself, terminated by a newline character.
räksmörgås.se
xn--rksmrgs-5wao1o.se
jas@latte:~$
Reading input from command line, and disabling copyright and license information:
jas@latte:~$ idn --quiet räksmörgås.se blåbærgrød.no
xn--rksmrgs-5wao1o.se
xn--blbrgrd-fxak7p.no
jas@latte:~$
Accessing a specific StringPrep profile directly:
jas@latte:~$ idn --quiet --profile=SASLprep --stringprep teßtª
teßta
jas@latte:~$
Getting character data encoded right, and making sure Libidn use the
same encoding, can be difficult. The reason for this is that most
systems encode character data in more than one character encoding,
i.e., using UTF-8 together with ISO-8859-1 or
ISO-2022-JP. This problem is likely to continue to exist until
only one character encoding come out as the evolutionary winner, or
(more likely, at least to some extents) forever.
The first step to troubleshooting character encoding problems with Libidn is to use the `--debug' parameter to find out which character set encoding `idn' believe your locale uses.
jas@latte:~$ idn --debug --quiet ""
system locale uses charset `UTF-8'.
jas@latte:~$
If it prints ANSI_X3.4-1968 (i.e., US-ASCII), this
indicate you have not configured your locale properly. To configure
the locale, you can, for example, use `LANG=sv_SE.UTF-8; export
LANG' at a /bin/sh prompt, to set up your locale for a Swedish
environment using UTF-8 as the encoding.
Sometimes `idn' appear to be unable to translate from your system
locale into UTF-8 (which is used internally), and you get an
error like the following:
jas@latte:~$ idn --quiet foo
idn: could not convert from ISO-8859-1 to UTF-8.
jas@latte:~$
The simplest explanation is that you haven't installed the `iconv' conversion tools. You can find it as a standalone library in GNU Libiconv (http://www.gnu.org/software/libiconv/). On many GNU/Linux systems, this library is part of the system, but you may have to install additional packages (e.g., `glibc-locale' for Debian) to be able to use it.
Another explanation is that the error is correct and you are feeding
`idn' invalid data. This can happen inadvertently if you are not
careful with the character set encodings you use. For example, if
your shell run in a ISO-8859-1 environment, and you invoke
`idn' with the `CHARSET' environment variable as follows,
you will feed it ISO-8859-1 characters but force it to believe
they are UTF-8. Naturally this will lead to an error, unless
the byte sequences happen to be parsable as UTF-8. Note that
even if you don't get an error, the output may be incorrect in this
situation, because ISO-8859-1 and UTF-8 does not in
general encode the same characters as the same byte sequences.
jas@latte:~$ idn --quiet --debug ""
system locale uses charset `ISO-8859-1'.
jas@latte:~$ CHARSET=UTF-8 idn --quiet --debug räksmörgås
system locale uses charset `UTF-8'.
input[0] = U+0072
input[1] = U+4af3
input[2] = U+006d
input[3] = U+1b29e5
input[4] = U+0073
output[0] = U+0078
output[1] = U+006e
output[2] = U+002d
output[3] = U+002d
output[4] = U+0072
output[5] = U+006d
output[6] = U+0073
output[7] = U+002d
output[8] = U+0068
output[9] = U+0069
output[10] = U+0036
output[11] = U+0064
output[12] = U+0035
output[13] = U+0039
output[14] = U+0037
output[15] = U+0035
output[16] = U+0035
output[17] = U+0032
output[18] = U+0061
xn--rms-hi6d597552a
jas@latte:~$
The sense moral here is to forget about `CHARSET' (configure your locales properly instead) unless you know what you are doing, and if you want to use it, do it carefully, after verifying with `--debug' that you get the desired results.