POSIX (Portable Operating System Interface)

Over the years, the POSIX specifications have continued to be revised and reorganized. At one time, each standard was informally named POSIX, followed There were also amendments to the base standard, such as IEEE Std 1003.1b-1993, which dealt with real-time extensions. However, all the various specifications have been rolled into one standard — IEEE Std 1003.1 — which was last updated in 2017 and published in 2018. Officially, it is called IEEE Std 1003.1-2017. However, it is also referred to as POSIX.1-2017 or, more informally, POSIX.1.

The POSIX standard goes The POSIX.1-2017 specifications define the fundamental services needed to build POSIX-compliant applications. They establish standard semantics and syntax to help developers write portable applications. POSIX.1 is made up of the following four volumes:

1. Base definitions. Provides common definitions for the specifications, including information about terms, concepts, syntax, service functions and command-line
2. System interfaces. Provides details about interface-related terms and concepts, and defines the functional interfaces available to applications accessing POSIX-conformant systems.
3. Shell and utilities. Describes the commands and utilities available to applications accessing POSIX-conformant systems, including the command language used in those systems.
4. Rationale. Includes historical information about the standard’s contents and why certain features were added or removed.