... and you thought ed was dead ...
Sed is a great tool used to transform data from one form into another. It uses regular expressions to perform operations on text. Unlike ed, it is pretty much non-interactive and makes only one pass over its data. However, it is very useful in shell scripts and makefiles to do lots of tasks, such as delete already-compiled files a-la make clean, or to take a winamp playlist, and extract paths from it. Sed can be great for pre-formatting everything2 posts! For example, use the command:
sed 's/</\</g;s/>/\>/g;s/\[/\[/g;s/\]/\]/g;' -
to pipe from stdin to stdout a file containing <s and ]s into its e2-friendly HTML-escaped equivalents. This technique is especially handy in working with indefinite or repeated data, as it does not depend on the input file being exactly the same each time, and can be a heck of a lot faster than editing by hand.