coreutils: Compatibility in ptx

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1 7.5.5 The GNU extensions to ‘ptx’
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1 This version of ‘ptx’ contains a few features which do not exist in
1 System V ‘ptx’.  These extra features are suppressed by using the ‘-G’
1 command line option, unless overridden by other command line options.
1 Some GNU extensions cannot be recovered by overriding, so the simple
1 rule is to avoid ‘-G’ if you care about GNU extensions.  Here are the
1 differences between this program and System V ‘ptx’.
1 
1    • This program can read many input files at once, it always writes
1      the resulting concordance on standard output.  On the other hand,
1      System V ‘ptx’ reads only one file and sends the result to standard
1      output or, if a second FILE parameter is given on the command, to
1      that FILE.
1 
1      Having output parameters not introduced by options is a dangerous
1      practice which GNU avoids as far as possible.  So, for using ‘ptx’
1      portably between GNU and System V, you should always use it with a
1      single input file, and always expect the result on standard output.
1      You might also want to automatically configure in a ‘-G’ option to
1      ‘ptx’ calls in products using ‘ptx’, if the configurator finds that
1      the installed ‘ptx’ accepts ‘-G’.
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1    • The only options available in System V ‘ptx’ are options ‘-b’,
1      ‘-f’, ‘-g’, ‘-i’, ‘-o’, ‘-r’, ‘-t’ and ‘-w’.  All other options are
1      GNU extensions and are not repeated in this enumeration.  Moreover,
1      some options have a slightly different meaning when GNU extensions
1      are enabled, as explained below.
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1    • By default, concordance output is not formatted for ‘troff’ or
1      ‘nroff’.  It is rather formatted for a dumb terminal.  ‘troff’ or
1      ‘nroff’ output may still be selected through option ‘-O’.
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1    • Unless ‘-R’ option is used, the maximum reference width is
1      subtracted from the total output line width.  With GNU extensions
1      disabled, width of references is not taken into account in the
1      output line width computations.
1 
1    • All 256 bytes, even ASCII NUL bytes, are always read and processed
1      from input file with no adverse effect, even if GNU extensions are
1      disabled.  However, System V ‘ptx’ does not accept 8-bit
1      characters, a few control characters are rejected, and the tilde
1      ‘~’ is also rejected.
1 
1    • Input line length is only limited by available memory, even if GNU
1      extensions are disabled.  However, System V ‘ptx’ processes only
1      the first 200 characters in each line.
1 
1    • The break (non-word) characters default to be every character
1      except all letters of the underlying character set, diacriticized
1      or not.  When GNU extensions are disabled, the break characters
1      default to space, tab and newline only.
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1    • The program makes better use of output line width.  If GNU
1      extensions are disabled, the program rather tries to imitate System
1      V ‘ptx’, but still, there are some slight disposition glitches this
1      program does not completely reproduce.
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1    • The user can specify both an Ignore file and an Only file.  This is
1      not allowed with System V ‘ptx’.
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