'ed' is bar far the best editor ever written. (I believe DOS even has it in 'edlin'). It is supported everywhere, mainly because it is about 1500 lines of portable code. Monks should love it because it forces you to get your regular expressions down pat. You only choice is to retype a line or regexp s/// it, so you get _GOOD_ at regular expressions fast or die. It even helps you empathize with the blind.

Hmm, I'm only mostly kidding. Most of what I learned from regexps was from coding on a mud that only supported ed (until I learned about ange-ftp for emacs, then ed died fast)