title: Exclude a directory from git diff
body: <p>I'm wondering how I can exclude an entire directory from my Git diff.  (In this case /spec).  I'm creating a diff for our entire software release using the git diff command.  However the changes to the specs are irrelevant for this procedure, and just create headaches.  now I know i can do</p>
  
  <pre><code>git diff previous_release..current_release app/
  </code></pre>
  
  <p>This would create a diff for all the changes in the app directory, but not for instance, in the lib/ directory.  Does anyone know how to accomplish this task?  Thanks!</p>
  
  <p>Edit:  I just want to be clear, I know I can just string the parameters of all of my directories on the end, minus /spec.  I was hoping there was a way to truly exclude a single directory in the command.</p>