title: find list of patterns from file not matching in another file unix
body: <p>I can't seem to be able to wrap my head around this simple problem.
  I need to print all patterns that are in fileA but not int fileB.</p>
  
  <p>Consider fileA to be as :</p>
  
  <pre><code>aaa
  bbb
  ccc
  ddd
  </code></pre>
  
  <p>And consider fileB to be as :</p>
  
  <pre><code>ppppppppppppp_aaa_ppppppppppppp
  ppppppppppppp_ccc_ppppppppppppp
  ppppppppppppp_ddd_ppppppppppppp
  </code></pre>
  
  <p>I want the following result :</p>
  
  <pre><code>bbb
  </code></pre>
  
  <p>I have tried </p>
  
  <pre><code>grep -f -v fileA fileB
  grep -F -v -f fileA fileB
  </code></pre>
  
  <p>but it does not seems to work as nothing is printed.</p>
  
  <p>How can I achieve this in a unix command?</p>
  
  <p>Thank you</p>