title: sed script to print the first three words in each line
body: <p>I wonder how can I do the following thing with sed:
  I need to keep only the first three words in each line.
  For example, the following text:</p>
  
  <pre><code>the quick brown fox jumps over the lazy bear
  the blue lion is hungry
  </code></pre>
  
  <p>will be transformed in:</p>
  
  <pre><code>the quick brown
  the blue lion
  </code></pre>