As Norman said, the earliest notation for pipes used an extension (or abuse) of the semantics of > and < . Warren's memory of what Salus wrote (it's on p. 52-53) is correct about the introduction of | (though I suspect that McIlroy (whom Salus quotes) is being kind to me when he said "he [Ken] couldn't bear to reveal my [Doug's] ugly syntax." Actually, I was responsible for the particular < and > syntax as implemented, although the whole idea came from much earlier on blackboard-only ideas, and the blackboard was Doug's. As to the original question: probably the ^ as an alternative to | (which does seem to be there from the start, i.e. 4th Edition) did have to do with character-set convenience on upper-case-only terminals. The TTY driver accepted \! as an escape for |, but this was somewhat of a pain. Dennis