SL (Steam Locomotive) runs across your terminal when you type "sl" as you meant to type "ls". It's just a joke command, and not useful at all. Now with a 1/10 chance of actually calling ls!
Copyright 1993,1998,2013 Toyoda Masashi (mtoyoda@acm.org) Edited 2013 by Jason Rosenman (jvrosenman@gmail.com)