Learning the bash Shell, Second Edition

The IEEE 1003.2 POSIX Shell Standard

There have been many attempts to standardize UNIX. Hardware companies’ monolithic attempts at market domination, fragile industry coalitions, marketing failures, and other such efforts are the stuff of history—and the stuff of frustration.

Only one standardization effort has not been tied to commercial interests: the Portable Operating System Interface, known as POSIX. This effort started in 1981 with the /usr/group (now UniForum) Standards Committee, which produced the /usr/group Standard three years later. The list of contributors grew to include the Institute of Electrical and Electronic Engineers (IEEE) and the International Organization for Standardization (ISO).

The first POSIX standard was published in 1988. This one, called IEEE P1003.1, covers low-level issues at the system-call level. IEEE P1003.2, covering the shell, utility programs, and user interface issues, was ratified in September 1992 after a six-year effort.

The POSIX standards were never meant to be rigid and absolute. The committee members certainly weren’t about to put guns to the heads of operating system implementors and force them to adhere. Instead, the standards are designed to be flexible enough to allow for both coexistence of similar available software, so that existing code isn’t in danger of obsolescence, and the addition of new features, so that vendors have the incentive to innovate. In other words, they are supposed to be the kind of third-party standards that ...