title: Remove blank lines between patterns
body: <p>I wish to remove blank lines(new lines, tabs and spaces) in the file with sed or awk, but only if those blank lines are in between two patterns.</p>
  
  <pre><code>lorem lorem PATTERN1
  
  \t
  
  PATTERN2 lorem2 lorem2`
  </code></pre>
  
  <p>I expect the result below which is a concatenation of 2 lines with both patterns.</p>
  
  <pre><code>lorem lorem PATTERN1PATTERN2 lorem2 lorem2
  </code></pre>