title: awk: find and replace in certain field only
body: <p>I have a text file like this:</p>
  
  <pre><code>$ cat test
  12 13 2100 s
  12 13 3100 s
  100 13 100 s
  12 13 300 s
  </code></pre>
  
  <p>I want the output to be like this:</p>
  
  <pre><code>$ cat test
  12 13 22000 s
  12 13 32000 s
  100 13 2000 s
  12 13 300 s
  </code></pre>
  
  <p>I only want to replace <code>100</code> in field 3 (once <code>100</code> is contained in <code>$3</code>) into <code>2000</code>. How can I accomplish this job using <code>awk</code>? </p>