This is a small Perl script used to mass-rename files using regular
expressions.
Example: massrename *.mp3 's/(.*?) (\d++)\.mp3/$2 - $1.mp3/'
This would switch track names like "Artist - Title 01.mp3" to "01 - Artist -
Title.mp3", for example.

A simpler example would be to change all spaces in all filenames in the current
directory to underscores:
massrename * 's/ /_/g'