title: 'Command "devenv.exe" is not valid' error in Visual Studio 2015 command window
body: <p>I am attempting to use the Visual Studio 2015 Command Window to in order to diff two files, using the command <code>devenv.exe /diff "C:\example.path" "C:\example.path"</code>. I received the following error:</p>
  
  <blockquote>
    <p>Command "devenv.exe" is not valid.</p>
  </blockquote>
  
  <p><code>devenv.exe</code> was missing from my computer so I repaired both my installation of (both) Visual Studio 2015 and Visual Studio 2013 to get it back.  However, I'm still getting the error when I attempt to run the <code>/diff</code> command.</p>
  
  <p>What steps should I take in order to resolve this issue?</p>