(coreutils) Standards conformance

Info Catalog (coreutils) Special built-in utilities (coreutils) Common options
 2.12 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
    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 have a newer system but are running
 software that assumes an older version of POSIX and uses `sort +1' or
 `tail +10', you can work around any compatibility problems by setting
 `_POSIX2_VERSION=199209' in your environment.
Info Catalog (coreutils) Special built-in utilities (coreutils) Common options
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