/tee'koh/ (Originally an acronym for "[paper] Tape Editor and COrrector"; later, "Text Editor and COrrector"]) A text editor developed at MIT and modified by just about everybody. With all the dialects included, TECO may have been the most prolific editor in use before Emacs, to which it was directly ancestral. The first Emacs editor was written in TECO.

It was noted for its powerful programming-language-like features and its unspeakably hairy syntax (see write-only language). TECO programs are said to resemble line noise. Every string of characters is a valid TECO program (though probably not a useful one); one common game used to be predict what the TECO commands corresponding to human names did.

As an example of TECO's obscurity, here is a TECO program that takes a list of names such as:

        Loser, J. Random
        Quux, The Great
        Dick, Moby

sorts them alphabetically according to surname, and then puts the surname last, removing the comma, to produce the following:

        Moby Dick
        J. Random Loser
        The Great Quux

The program is

        [1 J^P$L$$
        J <.-Z; .,(S,$ -D .)FX1 @F^B $K :L I $ G1 L>$$

(where ^B means "Control-B" (ASCII 0000010) and $ is actually an alt or escape (ASCII 0011011) character).

In fact, this very program was used to produce the second, sorted list from the first list. The first hack at it had a bug: GLS (the author) had accidentally omitted the "@" in front of "F^B", which as anyone can see is clearly the Wrong Thing. It worked fine the second time. There is no space to describe all the features of TECO, but "^P" means "sort" and "J" is an idiomatic series of commands for "do once for every line".

By 1991, Emacs had replaced TECO in hacker's affections but descendants of an early (and somewhat lobotomised) version adopted by DEC can still be found lurking on VMS and a couple of crufty PDP-11 operating systems, and ports of the more advanced MIT versions remain the focus of some antiquarian interest.

See also retrocomputing.

for VAX/VMS, Unix, MS-DOS, Macintosh, Amiga.