A pipe is a first-in-first-out interprocess communication channel. The pipe version as it is known today was invented by an American Computer Scientist Douglas McIlroy and incorporated into Version 3 AT&T UNIX in 1973 by Ken Thompson. It was inspired by the observation that frequently the output of one application is used as an input for another. This concept can be reused to connect a chain of processes. This is frequently observed in UNIX shell constructs that utilize the | operator.