If you use your Mac for any period of time, you will find the need to open a document with a different program other than the one set as default. The "Open With" menu appears in the Finder whenever you right-click or control-click on the icon of a document. The "Open With" command is designed to give you a list of alternative choices to handle the file that you've selected, but after long-term use you will find this list can get a little bit messy.
Duplicate entries in your "Open With" menu can be easily cleaned via a simple terminal command. We initially covered this command in a 2009 post about rebuilding your launch services, but this post is updated with video and a few new methods that'll work in OS X Mountain Lion. In the video below, I will demonstrate the basic terminal command. I will also show you how to create a bash script to make it easier to repeat this cleaning whenever needed, as well as create an Alfred workflow to do the same (requires the Alfred powerpack.)
Below you'll find the commands used in the video. If you are creating the .bash_profile alias method, remember you will have to quit and relaunch terminal for this to work.
Fix Duplicate "Open With" Terminal:
Fix Duplicate "Open With" via Bash alias:
If you are a little shy of monkeying around in terminal and bash, you can use utilities such as Onyx or Cocktail to get the job done.