title: grep (awk) a file from A to first empty line
body: <p>I need to grep a file from a line containing <code>Pattern A</code> to a first empty line. 
  I used <code>awk</code> but I don't know how to code this empty line.</p>
  
  <pre><code>cat ${file} | awk '/Pattern A/,/Pattern B/'
  </code></pre>