title: Add up a column of numbers at the Unix shell
body: <p>Given a list of files in <code>files.txt</code>, I can get a list of their sizes like this:</p>
  
  <pre><code>cat files.txt | xargs ls -l | cut -c 23-30
  </code></pre>
  
  <p>which produces something like this:</p>
  
  <pre><code>  151552
    319488
   1536000
    225280
  </code></pre>
  
  <p>How can I get the <strong>total</strong> of all those numbers?</p>