title: how to copy diff of two directories to a new directory?
body: <p>Suppose I have two directories : D1 and D2.</p>
  
  <p>D1 ( f1, f2, f3, f4 )
  D2 ( f1, f2 )</p>
  
  <p>I want to copy the files in D1 , which are not in D2, to another directory D3 :</p>
  
  <p>D3 ( f3, f4 )</p>
  
  <p>How do I do this in linux ?</p>
  
  <p>Thanx,
  trinity</p>