Apparently today is the 50th anniversary of using '|' for connecting shell pipelines. It was introduced in v4 of the Thompson shell, whose manpage is dated 1973-04-18 [1]. Previously the syntax for 'a | b' was `a >b>` [2].

[1]: https://www.in-ulm.de/~mascheck/bourne/v4/

[2]: https://www.in-ulm.de/~mascheck/bourne/v3/