If you need to add file extension for hundred of file in a folder this terminal command will save your life.

Run Terminal App on OS X then change working directory to the folder contains the files you want to add extension. Type line below; (or just copy & paste)

 

I’ve done this for 770 png file exported by Cinema4D (by accident) without file extension. It worked well, saved my day.

Resource: http://osxdaily.com/2012/11/22/add-file-extension-group-of-files-os-x/