title: exchange two words using sed
body: <p>I am trying to exchange two words in a line but it doesn't work. For example: &quot;Today is my first day of university&quot; should be &quot;my is Today first day of university&quot;</p>
  <p>This is what I tried:</p>
  <pre><code>sed 's/\([a-zA-z0-9]*\)\([a-zA-z0-9]*\)\([a-zA-z0-9]*\)/\3\2\1/' filename.txt
  </code></pre>
  <p>What am I doing wrong?</p>