POSIX

The Portable Operating System Interface (POSIX; IPA: ) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. In order to define a level of compatibility, POSIX specifies many aspects of functionality that can be classified as application programming interface (API), command-line shell, and shell commands. Originally derived from commonly-found Unix APIs, shells, and commands (partly because Unix was considered manufacturer-neutral), today many systems conform to the standard – including branded Unix systems, Unix-like systems, and many systems that were historically unrelated to Unix.

The standardized user command line and scripting interface were based on the UNIX System VBourne shell. Many user-level programs, services, and utilities (including awk, echo, ed) were also standardized, based on UNIX System V versions of them, along with required program-level services (including basic I/O: file, terminal, and network). POSIX also defines a standard threading library API which is supported by most modern operating systems.

The POSIX standard is developed by the Austin Group (a joint working group among the IEEE, The Open Group, and the ISO/IEC JTC 1/SC 22/WG 15).

POSIX is intended to be used by both application and system developers. System developers implement the interface imposed by POSIX, while application developers then use the POSIX interface to ensure compatibility across POSIX compliant systems.