title: Extract substring in Bash
body: <p>Given a filename in the form <code>someletters_12345_moreleters.ext</code>, I want to extract the 5 digits and put them into a variable.</p>
  
  <p>So to emphasize the point, I have a filename with x number of characters then a five digit sequence surrounded by a single underscore on either side then another set of x number of characters.  I want to take the 5 digit number and put that into a variable.</p>
  
  <p>I am very interested in the number of different ways that this can be accomplished.</p>