POSIX2

POSIX.2, commonly referred to as POSIX.2, is the Shell and Utilities part of the POSIX family of standards. It specifies a portable user-level interface for command-line tools and the command language used by the UNIX shell. The standard defines a broad set of utilities and their expected behavior, along with the syntax and semantics of the shell command language.

The scope of POSIX.2 includes common utilities such as cat, cp, mv, rm, ls, echo, test, and others, as well as text-processing tools like grep, sed, awk, tr, cut, paste, sort, uniq, join, wc, head, and tail. It also covers the shell language (the sh shell), including control structures, redirection, pipelines, and environment handling. The overarching goal is to promote portability of shell scripts and command-line programs across POSIX-compliant systems.

POSIX.2 was developed as part of the IEEE 1003 standards and has undergone several revisions since its initial publication in the 1990s. Over time, updates have aligned or integrated aspects of POSIX.2 with other POSIX baselines, and many of its utilities have been adopted widely in modern UNIX-like systems. Real-world implementations commonly appear in GNU core utilities or BSD-style userlands, typically aiming to conform to POSIX.2 behavior, while allowing platform-specific extensions.

Today, POSIX.2 remains a reference point for expected command-line interfaces and utility behavior on POSIX-compliant platforms, contributing to cross-system script portability and consistency in tool semantics.