@ed1conf
BTW, Re:

> Using \1, \2, etc to refer to regex captures

I had remembered that as an ex(1) enhancement. Did ed(1) indeed have regex captures, and I'm just misremembering?

@ed1conf @dougmerritt \1 \2 etc in the replacement string for s first appeared in the manual in the 6th Edition (May 1975), which means the code probably changed after the 5th Edition manual (June 1974). 6/e is when ed first gained \( \) in regular expressions as well, which makes sense because you can't have \1 without that.

Pedantically that means ed(1) had those things from its first appearance in 7/e (1979). The 7th is when the manual sections switched to Arabic numbers; 6/e and earlier used Roman numbers, so before 7/e it was ed(I), not ed(1).

My knowledge of history is not encyclopedic, but I have copies of all the early manuals, and an instinct for pedantry.