UPDATE: This method has been extended and superseded, find out about the “new improved” method here.
Web developers often have reason to fake a host name’s associated IP address by editing their /etc/hosts file.
The peculiarities of the development environment we use here at WordPress.com mean I find myself switching back and forth between two /etc/hosts configurations quite frequently. It started getting annoying to manually go into the /etc/hosts file and uncomment or re-comment entries all the time, so I came up with a quick and dirty solution to shortcut the process.
This solution involves creating two (or more) /etc/hosts files and writing a very short script for each which activates them.
The Unlettered Gentleman 