Shell Scripting: Expert Recipes for Linux, Bash, and More

Unix

In 1965, Bell Labs and GE joined a Massachusetts Institute of Technology (MIT) project known as MULTICS, the Multiplexed Information and Computing System. Multics was intended to be a stable, timesharing OS. The “Multiplexed” aspect added unnecessary complexity, which eventually led Bell Labs to abandon the project in 1969. Ken Thompson, Dennis Ritchie, Doug McIlroy, and Joe Ossanna retained some of the ideas behind it, took out a lot of the complexity, and came up with Unix (a play on the word MULTICS, as this was a simplified operating system inspired by MULTICS).

An early feature of Unix was the introduction of pipes — something that Doug McIlroy had been thinking about for a few years and was implemented in Unix by Ken Thompson. Again, it took the same notion of streamed serial data, but pipes introduced the idea of having stdin and stdout, through which the data would flow. Similar things had been done before, and the concept is fairly simple: One process creates output, which becomes input to another command. The Unix pipes method introduced a concept that dramatically affected the design of the rest of the system.

Most commands have a file argument as well, but existing commands were modified to default to read from their “Standard Input” (stdin) and “Standard Output” (stdout); the pipe can then “stream” the data from one tool to another. This was a novel concept, and one that strongly defines the Unix shell; it makes the whole system a set of generically useful tools, ...