title: How do I remove a line that does not contain a specific character?
body: <p>For example, I want do remove all lines in a textile that do not contain the character '@'</p>
  
  <p>I have already tried to use sed like so</p>
  
  <pre><code>sed '/@/!d' data.txt
  </code></pre>
  
  <p>What am I missing? Shouldn't this work?</p>