Specification
SUSv3 totals some 3700 pages, which are thematically divided into four main parts:
- Base Definitions (XBD) - a list of definitions and conventions used in the specifications and a list of C header files which must be provided by compliant systems. 84 header files in total are provided.
- Shell and Utilities (XCU) - a list of utilities and a description of the shell, sh. 160 utilities in total are specified.
- System Interfaces (XSH) - contains the specification of various functions which are implemented as system calls or library functions. 1123 system interfaces in total are specified.
- Rationale (XRAT) - the explanation behind the standard.
The standard user command line and scripting interface is the POSIX shell, an extension of the Bourne Shell based on an early version of the Korn Shell. Other user-level programs, services and utilities include awk, echo, ed, vi, and hundreds of others. Required program-level services include basic I/O (file, terminal, and network) services. A test suite accompanies the standard. It is called PCTS or the POSIX Certification Test Suite.
Additionally, SUS includes CURSES (XCURSES) specification, which specifies 372 functions and 3 header files. All in all, SUSv3 specifies 1742 interfaces.
Note that a system need not include source code derived in any way from AT&T Unix to meet the specification. For instance, IBM OS/390, now z/OS, qualifies as a "Unix" despite having no code in common.
Read more about this topic: Single UNIX Specification