title: "git show HEAD" results in "fatal : ambiguous 'HEAD': unknown revision or path not in the working tree"
body: <p>I'm trying to fix a problem with <code>git</code>. </p>
  
  <p>When I enter <code>git show HEAD</code>, I got the error <code>fatal : ambiguous 'HEAD': unknown revision or path not in the working tree</code>.</p>
  
  <p>What could I do to fix this problem?</p>
  
  <p>The display of <code>git status</code> is : </p>
  
  <pre><code>git status
  On branch master
  
  Initial commit
  
  Changes to be committed:
    (use "git rm --cached &lt;file&gt;..." to unstage)
  
      new file:   script.txt
  
  Untracked files:
    (use "git add &lt;file&gt;..." to include in what will be committed)
  
      script.txt~
  </code></pre>