title: Editing a column in a text file using shell script
body: <p>I have a text file:</p>
  
  <pre><code>a b n
  d f h 
  e f y
  </code></pre>
  
  <p>I want to edit it and make it like:</p>
  
  <pre><code>a b@gmail.com n
  d f@gmail.com h 
  e f@gmail.com y
  </code></pre>
  
  <p>How can I do this? Is there any command which can help?</p>