title: How to trigger unison sync files and directories when there's any change on OSX?
body: <p>I have a need to sync two directories on OSX. I find <a href="https://stackoverflow.com/questions/2936627/two-way-sync-with-rsync">this post</a> recommending using unison.  </p>
  
  <p>I tried unison, it seems it can sync two directories very well. But it doesn't do synchronization automatically( always keep two directories synced when there's any change ).  </p>
  
  <p>So I guess to accomplish my purpose, unison should be used with a trigger which will watch changes and notify unison to do its work.</p>
  
  <p>But how to do that? Any recommendation and tutorial? </p>