Show hidden files in Finder

By default, Mac OS X's Finder keeps system files - which generally start with a dot, like .bash_profile - out of your sight.

But that makes editing one of these files extremely difficult if you, say, want to customize your Terminal prompt. To do so without firing up vim (if you don't know, don't ask), set Finder to show all hidden files. OS X FAQ has the details on how to do it.

In the Terminal type:
defaults write com.apple.finder AppleShowAllFiles TRUE
killall Finder

To set it back (that .DS_Store on the Desktop is hella irritating), execute those same commands, but just switch that TRUE to FALSE. Handy. — Gina Trapani

The Finder II - Show Hidden Files [OS X FAQ]