title: How to show git commit using number of commits since a tag
body: <p>With <code>git describe</code> you can get the number of commits since the last tag.  If you only had the tag and the number of commits what is the best way to show the commit that was described?</p>
  
  <p>I know you could use <code>git log tag..</code> and pipe it to a a script that does the counting but I was hoping for a more elegant solution similar to <code>git show tag~n</code>. </p>
  
  <p>To add more context, we are planning using <code>git describe</code> to create release numbers, for example with </p>
  
  <pre><code>$ git describe
  v1.5-39-g5ede964
  </code></pre>
  
  <p>we would use foo_1.5.39.   What we would like to do is knowing 1.5.39 means the 39th commit after the v1.5 tag, find that commit, i.e. find g5ede964.   As pointed out in a comment, the 39th commit after v1.5 may not be unique.  So perhaps a better way to ask this is what is the best way to find all commits X such that if HEAD was pointing to X <code>git describe</code> would return 
  <code>v1.5-39-*****</code>.   </p>