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Node:Standards conformance, Next:, Previous:Invoking sdiff, Up:Top

Standards conformance

In a few cases, the GNU utilities' default behavior is incompatible with the POSIX standard. To suppress these incompatibilities, define the POSIXLY_CORRECT environment variable. Unless you are checking for POSIX conformance, you probably do not need to define POSIXLY_CORRECT.

Normally options and operands can appear in any order, and programs act as if all the options appear before any operands. For example, diff lao tzu -C 2 acts like diff -C 2 lao tzu, since 2 is an option-argument of -C. However, if the POSIXLY_CORRECT environment variable is set, options must appear before operands, unless otherwise specified for a particular command.

Newer versions of POSIX are occasionally incompatible with older versions. For example, older versions of POSIX allowed the command diff -c -10 to have the same meaning as diff -C 10, but POSIX 1003.1-2001 diff no longer allows digit-string options like -10.

The GNU utilities normally conform to the version of POSIX that is standard for your system. To cause them to conform to a different version of POSIX, define the _POSIX2_VERSION environment variable to a value of the form yyyymm specifying the year and month the standard was adopted. Two values are currently supported for _POSIX2_VERSION: 199209 stands for POSIX 1003.2-1992, and 200112 stands for POSIX 1003.1-2001. For example, if you are running older software that assumes an older version of POSIX and uses diff -c -10, you can work around the compatibility problems by setting _POSIX2_VERSION=199209 in your environment.


 
 
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