scope:

POSIX.1-2008 defines a standard operating system interface and environment, including a command interpreter (or ''shell''), and common utility programs to support applications portability at the source code level. It is intended to be used by both application developers and system implementors.

POSIX.1-2008 comprises four major components (each in an associated volume):

1. General terms, concepts, and interfaces common to all volumes of POSIX.1-2008, including utility conventions and C-language header definitions, are included in the Base Definitions volume of POSIX.1-2008.

2. Definitions for system service functions and subroutines, language-specific system services for the C programming language, function issues, including portability, error handling, and error recovery, are included in the System Interfaces volume of POSIX.1-2008.

3. Definitions for a standard source code-level interface to command interpretation services (a ''shell'') and common utility programs for application programs are included in the Shell and Utilities volume of POSIX.1-2008.

4. Extended rationale that did not fit well into the rest of the document structure, containing historical information concerning the contents of POSIX.1-2008 and why features were included or discarded by the standard developers, is included in the Rationale (Informative) volume of POSIX.1-2008.