title: awk a number, character, then the same number
body: <p>I have a column of values where the field begins with n/n: and where n is a number between 0 and 20. </p>
  
  <p>Other columns also contain "n/n:" information; I only want to filter based on a single specific column.</p>
  
  <p>"n/n:" can be a combination of any pair of numbers between 0 and 20 (ex. 0/1:, 1/1:, 1/19:, 19/19:)</p>
  
  <p>I would like to filter lines in the file where the first and second n are the same number in the column of interest (0/0, 1/1,... 20/20).</p>
  
  <p>Rather than do this once for each combination of numbers (each iteration would take a long time): </p>
  
  <pre><code>awk '$col !~ /^n\/n:/' file &gt; filtered.file
  </code></pre>
  
  <p>... I'm hoping there's a more concise, better way.</p>
  
  <p>An example of the file</p>
  
  <pre><code> 1/1: 0/1: a
   1/2: 1/1: b
   0/1: 2/2: c
   3/3: 0/2: d
   0/2: 0/1: e
  </code></pre>
  
  <p>Desired output, filtered based on col2</p>
  
  <pre><code> 1/1: 0/1: a
   3/3: 0/2: d
   0/2: 0/1: e
  </code></pre>