POSIXVERSION

POSIXVERSION is an environment variable defined by the Portable Operating System Interface (POSIX) standard. It indicates the version of the POSIX standard that the system claims to support. The value of POSIXVERSION is a string that represents the year and, optionally, the technical corrigendum level of the POSIX standard.

The format of the POSIXVERSION string is "YYYYMML", where "YYYY" is the year of the standard, "MM" is the month, and "L" is the technical corrigendum level. For example, a system conforming to the 2008 edition of the POSIX standard with no technical corrigendum would have a POSIXVERSION of "200809". If a technical corrigendum were applied, it would be indicated by an additional letter, such as "200809a" for the first corrigendum.

The POSIXVERSION variable is used by applications to determine the level of POSIX compliance of the system. It allows applications to adjust their behavior based on the features and capabilities provided by the POSIX standard supported by the system. However, it is important to note that the actual level of POSIX compliance may vary, and the POSIXVERSION variable should be used as a guide rather than a definitive indicator.

The POSIXVERSION variable is typically set by the system administrator or during the system installation process. It can be queried using standard shell commands, such as "echo $POSIXVERSION", and is an important aspect of ensuring compatibility and portability of applications across different POSIX-compliant systems.