title: finding duplicates in a field and printing them in unix bash
body: <p>I have a file the contains</p>
  
  <pre><code>apple
  apple
  banana
  orange
  apple
  orange
  </code></pre>
  
  <p>I want a script that finds the duplicates apple and orange and tells the user that the following : apple and orange are repeated.
  I tried </p>
  
  <pre><code>nawk '!x[$1]++' FS="," filename
  </code></pre>
  
  <p>to find repeated item
  so how can i print them out in unix bash ?</p>