Understanding POSIX compliance

Way back in the Stone Age of Computing, there was no such thing as standardization. In order to keep things relevant, let’s begin our history with the advent of Unix.

AT&T, who created Unix in the early 1970s, wasn’t allowed to market it until 1983. This was due to an anti-trust legal case that the U.S. government had filed against AT&T back in 1956. (I don’t know the details of the case, so please don’t ask.) But, they were allowed to license the code to other vendors so that they could sell their own modified implementations. Because of this, several different implementations of Unix emerged, which weren’t always completely compatible with each other. These different implementations included the Berkeley Software Distribution (BSD), Microsoft Xenix, and SunOS. In 1983, AT&T was finally allowed to market its own System V Unix. Making things more interesting was the wide variety of shells that eventually...