To start, open up Automator (in the Applications folder) and choose a Service template. From the library choose "Run Shell Script" and drag it across to the workflow area. In the text box paste the following command:
STATUS=`defaults read com.apple.finder AppleShowAllFiles`
if [ $STATUS == YES ];
then
defaults write com.apple.finder AppleShowAllFiles NO
else
defaults write com.apple.finder AppleShowAllFiles YES
fi
killall Finder