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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
.
Newer versions of POSIX are occasionally incompatible with older versions. For example, older versions of POSIX required the command `sort +1' to sort based on the second and succeeding fields in each input line, but starting with POSIX 1003.1-2001 the same command is required to sort the file named `+1', and you must instead use the command `sort -k 2' to get the field-based sort.
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 `sort +1', you
can work around the compatibility problems by setting
`_POSIX2_VERSION=199209' in your environment.