[lapsed_lisper]

Unix's standard error is definitely not the first invention of a sink for errors. According to Doug McIlroy, Unix got standard error in its 6th Edition, released in May 1975 (http://www.cs.dartmouth.edu/~doug/reader.pdf). 5th Edition was released in June, 1974, so it's reasonable to suppose Unix's standard error was developed during that 11 month interval. By that time, Multics already had a dedicated error stream, called error_output (see https://multicians.org/mtbs/mtb763.html, dated October 1973).

All the same, I'd be willing to believe that Unix's standard error could have been an "independent rediscovery" of one feature made highly desirable by other features (redirection and pipes). It's not clear how much communication there was among distinct OS researcher groups back then, so even if other systems had an analogue, Bell Labs people might not have been aware of it.

[dbcurtis]

The story that I recall about the origins of stderr is that without it, pipes are a mess. Keeping stdout to just the text that you want to pipe between tools and diverting all “noise” elsewhere is what makes pipes useable.

[kragen]

the article is about specifically what kind of mess and what kind of usability problems inspired the change