title: Git - easiest way to see diff with previous version if I have the sha
body: <p>A colleague of mine checked in some changes to Git, and I want to see exactly what those changes were.  In other words, the diff between his check-in and its parent.</p>
  <p>What seemed logical to me was to run this command:</p>
  <pre><code>git diff shaOfHisCheckIn
  </code></pre>
  <p>But this didn't work.  It appears to show the diff between that SHA and my current working copy.</p>
  <p>What's the correct command to show the diff between a given SHA and its parent?</p>