Xcode for the Rest of Us, Part II
Subject:   Easy way to add "Compare Files" to finder contextual menu
Date:   2010-05-19 07:45:42
From:   aaronjlwebb
In automator, create a new service with the following settings:

Service receives selected __files or folders__ in __Finder.app__

Shell __/bin/bash__
Pass input: __as arguments__

In shell input box, remove 'cat' and replace with:
/usr/bin/opendiff $1 $2

Save as 'Compare Files' (or whatever you want).

Voila - you can now select 2 items in finder and diff them with a right-click and 'Compare Files' menu item.