title: how to join files in unix without sorting
body: <p>I am trying to join 2 csv files based on a key in unix. </p>
  
  <p>My files are really huge 5GB each and sorting them is taking too long.</p>
  
  <p>I want to repeat this procedure for 50 such joins.</p>
  
  <p>Can someone tell me how to join without sorting and quickly.</p>