title: awk delete all lines not containing substring using if condition
body: <p>I want to delete lines where the first column does not contain the substring 'cat'.
  So if string in col 1 is 'caterpillar', i want to keep it. </p>
  
  <pre><code>awk -F"," '{if($1 != cat) ... }' file.csv
  </code></pre>
  
  <p>How can i go about doing it?</p>