(coreutils.info)Compatibility in ptx

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7.5.5 The GNU extensions to ‘ptx’
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This version of ‘ptx’ contains a few features which do not exist in
System V ‘ptx’.  These extra features are suppressed by using the ‘-G’
command line option, unless overridden by other command line options.
Some GNU extensions cannot be recovered by overriding, so the simple
rule is to avoid ‘-G’ if you care about GNU extensions.  Here are the
differences between this program and System V ‘ptx’.

   • This program can read many input files at once, it always writes
     the resulting concordance on standard output.  On the other hand,
     System V ‘ptx’ reads only one file and sends the result to standard
     output or, if a second FILE parameter is given on the command, to
     that FILE.

     Having output parameters not introduced by options is a dangerous
     practice which GNU avoids as far as possible.  So, for using ‘ptx’
     portably between GNU and System V, you should always use it with a
     single input file, and always expect the result on standard output.
     You might also want to automatically configure in a ‘-G’ option to
     ‘ptx’ calls in products using ‘ptx’, if the configurator finds that
     the installed ‘ptx’ accepts ‘-G’.

   • The only options available in System V ‘ptx’ are options ‘-b’,
     ‘-f’, ‘-g’, ‘-i’, ‘-o’, ‘-r’, ‘-t’ and ‘-w’.  All other options are
     GNU extensions and are not repeated in this enumeration.  Moreover,
     some options have a slightly different meaning when GNU extensions
     are enabled, as explained below.

   • By default, concordance output is not formatted for ‘troff’ or
     ‘nroff’.  It is rather formatted for a dumb terminal.  ‘troff’ or
     ‘nroff’ output may still be selected through option ‘-O’.

   • Unless ‘-R’ option is used, the maximum reference width is
     subtracted from the total output line width.  With GNU extensions
     disabled, width of references is not taken into account in the
     output line width computations.

   • All 256 bytes, even ASCII NUL bytes, are always read and processed
     from input file with no adverse effect, even if GNU extensions are
     disabled.  However, System V ‘ptx’ does not accept 8-bit
     characters, a few control characters are rejected, and the tilde
     ‘~’ is also rejected.

   • Input line length is only limited by available memory, even if GNU
     extensions are disabled.  However, System V ‘ptx’ processes only
     the first 200 characters in each line.

   • The break (non-word) characters default to be every character
     except all letters of the underlying character set, diacriticized
     or not.  When GNU extensions are disabled, the break characters
     default to space, tab and newline only.

   • The program makes better use of output line width.  If GNU
     extensions are disabled, the program rather tries to imitate System
     V ‘ptx’, but still, there are some slight disposition glitches this
     program does not completely reproduce.

   • The user can specify both an Ignore file and an Only file.  This is
     not allowed with System V ‘ptx’.