title: using comm to diff two files
body: <p>I am trying to use comm to compute the difference between two sorted files, however the result doesn't make sense, what's wrong?  I want to show the strings that exists in test2 but not test1, and then show the strings that exist in test1 but not test2</p>
  
  <pre>
  >test1
  a
  b
  d
  g
  
  >test2
  e
  g 
  k
  p
  
  >comm test1 test2
  a
  b
  d
      e
  g
      g 
      k
      p
  </pre>