title: Getting a "bad interpreter" error when using brew
body: <p>I'm getting this error when I try to run any brew command.</p>
  
  <pre><code>Holger-Sindbaeks-MacBook-Air:~ holgersindbaek$ brew help
  -bash: /usr/local/bin/brew: /usr/bin/ruby: bad interpreter: No such file or directory
  </code></pre>
  
  <p>I have absolutely no idea on how to fix this and been searching for a long time without answer.</p>