LPRng-HOWTO: 15 Oct 2001 (For LPRng-3.7.9)
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# 6.12. Fixing Bad Control Files and Metacharacters

Options used:

- `safe_chars=`additional safe characters for control file

RFC1179 defines a simple protocol and standard for print jobs to be interchanged between print spooling systems. Unfortunately, there were some major mistakes in not specifying the exact form that text would take when placed in the control file.

By default, LPRng will brutally convert a non-conforming RFC1179 control file into one that is acceptable to most, if not all, existing RFC1179 implementations. In order to prevent problems with LPRng ruthlessly purges all characters but upper and lower case letters, spaces, tabs, and `-_.@/:()=,+-%` from the control file, replacing suspicious characters with underscore (`_`). In addition, LPRng will ruthlessly regenerate control file entries and data file names so that they are compliant with all known RFC1179 implementations.

For some installations, the default set of safe characters may be overly restrictive. For example, vintage software may generate files with `#` characters in the `J` line of the control file. The replacement of this character by underscore (`_`) may cause other applications which use the control file information to stop working. The `:safe_chars` option allows the user to specify an additional set of safe characters in the `lpd.conf` configuration file(s).

For example, `:safe_chars=#"` would allow the `#` and `"` characters to appear in the control file.

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