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POSIX (The Portable Operating System Interface)
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   The GNU library is also compatible with the ISO "POSIX" family of
standards, known more formally as the "Portable Operating System
Interface for Computer Environments" (ISO/IEC 9945).  They were also
published as ANSI/IEEE Std 1003.  POSIX is derived mostly from various
versions of the Unix operating system.

   The library facilities specified by the POSIX standards are a
superset of those required by ISO C; POSIX specifies additional
features for ISO C functions, as well as specifying new additional
functions.  In general, the additional requirements and functionality
defined by the POSIX standards are aimed at providing lower-level
support for a particular kind of operating system environment, rather
than general programming language support which can run in many diverse
operating system environments.

   The GNU C library implements all of the functions specified in
`ISO/IEC 9945-1:1996, the POSIX System Application Program Interface',
commonly referred to as POSIX.1.  The primary extensions to the ISO C
facilities specified by this standard include file system interface
primitives (Note: File System Interface), device-specific terminal
control functions (Note: Low-Level Terminal Interface), and process
control functions (Note: Processes).

   Some facilities from `ISO/IEC 9945-2:1993, the POSIX Shell and
Utilities standard' (POSIX.2) are also implemented in the GNU library.
These include utilities for dealing with regular expressions and other
pattern matching facilities (Note: Pattern Matching).