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’.
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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.
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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.
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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.
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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.
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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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