title: How to remove first 3 character
body: <p>I have a file with following data:</p>
  
  <pre><code>KP_site1
  KP_site2
  KP_site3
  </code></pre>
  
  <p>I want following output:</p>
  
  <pre><code>site1
  site2
  site3
  </code></pre>
  
  <p>How can I achieve this in perl regex?</p>