title: Why do I get "undefined method `start_with?'"?
body: <p>I get:</p>
  
  <pre><code>undefined method 'start_with?' for "-f":String (NoMethodError)
  </code></pre>
  
  <p>At this line: </p>
  
  <pre><code>if arg.start_with?("-v")
  </code></pre>
  
  <p>This worked on a different machine apparently so I'm assuming it could be a problem with my Ruby installation. Any ideas?</p>