title: Reverse input order with sed
body: <p>I have a file, lets call it 'a.txt' and this file contains the following text line</p>
  
  <pre><code>do to what
  </code></pre>
  
  <p>I'm wondering what the SED command is to reverse the order of this text to make it look like</p>
  
  <pre><code>what to do
  </code></pre>
  
  <p>Do I have to do some sort of append? Like append 'do' to 'to' so it would look like</p>
  
  <p>to ++ do (used ++ just to make it clear)</p>