title: how to replace all lines between two points and subtitute it with some text in sed
body: <p>Suppose I have this text:</p>
  
  <pre><code>BEGIN
  hello
  world
  how
  are
  you
  END
  </code></pre>
  
  <p>How to convert it to bellow text using sed command in linux:</p>
  
  <pre><code>BEGIN
  fine, thanks
  END
  </code></pre>