title: Use compgen to get autocomplete for another command, which flag to use?
body: <p>I have a custom auto-completed command (call it <code>commandA</code>)</p>
  
  <p>in <code>commandB</code> I want to steal the autocomplete options for the first argument to commandA</p>
  
  <p>So, for example the options for argument1 for commandA are:</p>
  
  <p><code>abcdef</code>
  <code>abcabc</code>
  <code>abc123</code></p>
  
  <p>I would like something along the lines of
  <code>compgen -? "commandA"</code> or <code>compgen -? "commandA abc"</code> to generate the list above.</p>