title: Get list of variables whose name matches a certain pattern
body: <p>In bash  </p>
  
  <pre><code>echo ${!X*}
  </code></pre>
  
  <p>will print all the names of the variables whose name starts with 'X'.<br>
  Is it possible to get the same with an arbitrary pattern, e.g. get all the names of the variables whose name contains an 'X' in any position?</p>