And a bunch of other things. See my article series on "Sed One-Liners Explained":

http://www.catonmat.net/blog/sed-one-liners-explained-part-o...

Sed is actually Turing complete. You'd never want to do it, but you can.

It's in the same class of things as the BASIC interpreter written as troff macros, really.

$('body').css('word-spacing', 10);

God I love firebug and jQuery.