title: Can ack find files based on filename only?
body: <p>Using <a href="http://betterthangrep.com/">ack</a> (sometimes packaged as ack-grep) I know that I can find <em>paths</em> that contain a specific string by doing:<br>
  <code>ack -g somestring</code></p>
  
  <p>But what if I only want files which have "somestring" in their <em>filenames</em>?</p>