title: Meaning of <=> (less than, equal, greater than) in Perl?
body: <p>In <a href="https://stackoverflow.com/questions/328673/how-can-i-find-the-newest-created-file-in-a-directory/328911#328911">this answer</a>, I saw the syntax <code>&lt;=&gt;</code>; what does this mean?  It seems to be some sort of comparison based on the context, but that's all I can gather.  Partial context:</p>
  
  <pre><code>sub rev_by_date { $b-&gt;[9] &lt;=&gt; $a-&gt;[9] }
  my @sorted_files = sort rev_by_date @files;
  </code></pre>