title: extracting unique values between 2 sets/files
body: <p>Working in linux/shell env, how can I accomplish the following:</p>
  
  <p>text file 1 contains:</p>
  
  <pre><code>1
  2
  3
  4
  5
  </code></pre>
  
  <p>text file 2 contains:</p>
  
  <pre><code>6
  7
  1
  2
  3
  4
  </code></pre>
  
  <p>I need to extract the entries in file 2 which are not in file 1. So '6' and '7' in this example. </p>
  
  <p>How do I do this from the command line? </p>
  
  <p>many thanks!</p>