title: How do you detect a "word" on a line that contains both letters and numbers?
body: <p>I need a regex that detects a "word" on a line that contains both letters and numbers and is a certain length, e.g. <code>812d555c726d10c77b05cd164705665a</code>. The goal is to detect lines that contain sha1 digests. </p>
  
  <p>If a regex-only is too hard, a Ruby solution is OK.</p>