title: Remove empty lines in a text file via grep
body: <p><code>FILE</code>:</p>
  
  <pre><code>hello
  
  world
  
  foo
  
  bar
  </code></pre>
  
  <p>How can I remove all the empty new lines in this <code>FILE</code>?</p>
  
  <p>Output of command:</p>
  
  <p><code>FILE</code>:</p>
  
  <pre><code>hello
  world
  foo
  bar
  </code></pre>