title: How can i display the second matched regex in sed
body: <p>Suppose I have this text</p>
  
  <pre>The code for 233-CO is the main reason for 45-DFG and this 45-GH</pre>
  
  <p>Now I have this regexp  <code>\s[0-9]+-\w+</code> which matches <code>233-CO</code>, <code>45-DFG</code> and <code>45-GH</code>.</p>
  
  <p>How can I display just the third match <code>45-GH</code>?</p>
  
  <pre><code>sed -re 's/\s[0-9]+-\w+/\3/g' file.txt
  </code></pre>
  
  <p>where <code>\3</code> should be the third regexp match.</p>