title: Remove all files except files with certain extension
body: <p>This removes all files that end with <code>.a</code> or <code>.b</code></p>
  
  <pre><code>$ ls *.a
  a.a  b.a  c.a
  
  $ ls *.b
  a.b  b.b  c.b
  
  $ rm *.a *.b
  </code></pre>
  
  <p>How would I do the opposite and remove all files that end with <code>*.*</code> except the ones that end with <code>*.a</code> and <code>*.b</code>?</p>