title: How do I pipe comm outputs to a file?
body: <p>I've used the comm command to compare two files, but I'm unable to pipe it to a third file:</p>
  
  <pre><code>comm file1 file2 &gt; file3 
  
  comm: file 1 is not in sorted order
  comm: file 2 is not in sorted order
  </code></pre>
  
  <p>How do I do this? <strong>The files are sorted already.</strong></p>
  
  <p>(comm file1 file2 works and prints it out)</p>
  
  <p>sample input:<br>
  file1:</p>
  
  <pre><code>21
  24
  31
  36
  40
  87
  105
  134
  ...
  </code></pre>
  
  <p>file2:</p>
  
  <pre><code>10
  21
  31
  36
  40
  40
  87
  103
  ...
  </code></pre>
  
  <p>comm file1 file2: works</p>
  
  <pre><code>comm file1 file2 &gt; file3 
  
  comm: file 1 is not in sorted order
  comm: file 2 is not in sorted order
  </code></pre>