How can I batch rename files using the Terminal?

Question

I have a set of files, all of them nnn.MP4.mov. How could I rename them so that it is just nnn.mov?

Answer 1

OS X has a Rename Files… contextual menu item which is invoked when you select two or more files in Finder. Provides the same function as the Automator answer up above. Though Automator provides you with the tools to go further if you wish.

(I know OP asked for Terminal but 33 others like Automator response)