The common name for the "IEEE Std 1003.2-1992, the POSIX Shell and Utilities standard". There are four main points to the standard, as follows:
- Shell syntax and command language. Special builtins such as cd and exec are defined.
- Utilities to be called by shell scripts and applications (sed, tr, and awk), shell builtins (test, kill) An expansion of this section's scope, termed the User Portability Extension has standardized interactive programs such as vi and mailx.
- Functional interfaces to services provided by the shell, shell word expansions, filename expansion (globbing), POSIX.2 system configuration variables, retrieve environment variables.
- A suite of "development" utilities such as c89 (the POSIX.2 version of cc), and yacc.
Most UNIX shells follow this standard and even MSDOS managed to follow a few of the guidelines. However, the standard is rather spare, so there are extensions galore (POSIX.2 makes no mention of even loggin into a shell...)
Information grepped and paraphrased from "Bash - The GNU shell" by Chet Ramey (version 2.03) and from the GLIBC manual (v0.02). Errors in this are mine, so give me a holler to fix it, or add and expand it.