title: How do I setup DiffMerge with msysgit / gitk?
body: <p>I've just started using Git and it's possible I've missed something obvious, but here goes:</p>
  
  <ul>
  <li>I'm using msysgit 1.6.2.2 on Windows XP</li>
  <li>While installing, I picked option 1 to "Use Git Bash only"</li>
  </ul>
  
  <p>I'm trying to put together a wrapper script that I can use to replace the built in git diff with DiffMerge. Based on <a href="https://stackoverflow.com/questions/255202/how-do-i-view-git-diff-output-with-visual-diff-program">this thread</a> on SO, I created the following batch file:</p>
  
  <pre><code>@echo off
  REM ---- Switch forward slashes to back slashes ----
  set oldW=%2
  set oldW=%oldW:/=\%
  set newW=%5
  set newW=%newW:/=\%
  
  REM ---- Launch DiffMerge ----
  "C:/Programs/SourceGear/DiffMerge/DiffMerge.exe" /title1="Old Version" %oldW% /title2="New Version" %newW%
  </code></pre>
  
  <p>I placed the bat file under %GIT_INSTALL%/cmd and edited my .gitconfig file as follows:</p>
  
  <pre><code>[diff]
  external = C:/Programs/git/cmd/git-diff-wrapper.bat
  </code></pre>
  
  <p>If i launch Git Bash and execute
      git diff HEAD HEAD~ -- myfile</p>
  
  <p>I get a message <code>File (\dev\null) not found</code> - which given I'm on Windows is not surprising.</p>
  
  <p>Pressing on, I launched gitk and under Edit>Preferences, I chose the same wrapper script. Trying the "external diff" option for a particular file gives the cryptic error message <code>Unknown Option "</code></p>
  
  <p>Clearly, I have no idea what I'm doing anymore so any help would be much appreciated.</p>