diffutils: Standards conformance

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1 17 Standards conformance
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1 In a few cases, the GNU utilities' default behavior is incompatible with
1 the POSIX standard.  To suppress these incompatibilities, define the
1 'POSIXLY_CORRECT' environment variable.  Unless you are checking for
1 POSIX conformance, you probably do not need to define 'POSIXLY_CORRECT'.
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1    Normally options and operands can appear in any order, and programs
1 act as if all the options appear before any operands.  For example,
1 'diff lao tzu -C 2' acts like 'diff -C 2 lao tzu', since '2' is an
1 option-argument of '-C'.  However, if the 'POSIXLY_CORRECT' environment
1 variable is set, options must appear before operands, unless otherwise
1 specified for a particular command.
1 
1    Newer versions of POSIX are occasionally incompatible with older
1 versions.  For example, older versions of POSIX allowed the command
1 'diff -c -10' to have the same meaning as 'diff -C 10', but POSIX
1 1003.1-2001 'diff' no longer allows digit-string options like '-10'.
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1    The GNU utilities normally conform to the version of POSIX that is
1 standard for your system.  To cause them to conform to a different
1 version of POSIX, define the '_POSIX2_VERSION' environment variable to a
1 value of the form YYYYMM specifying the year and month the standard was
1 adopted.  Two values are currently supported for '_POSIX2_VERSION':
1 '199209' stands for POSIX 1003.2-1992, and '200112' stands for POSIX
1 1003.1-2001.  For example, if you are running older software that
1 assumes an older version of POSIX and uses 'diff -c -10', you can work
1 around the compatibility problems by setting '_POSIX2_VERSION=199209' in
1 your environment.
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