Why would you want to do this?
I use my RPi for XBMC and as a web server (yet to reinstall after switching to Raspbmc). I do not always want XBMC running, as I am not always home and also not always watching films! So in the interests of saving system resources I wanted to stop XBMC and shut off the HDMI to stop any TV interference. There are two commands to do this, but they are quite long and not easy to remember! I needed something to shorten this process. Preferably xbmc start/stop.
This is how I implemented it.