title: Select a string between two others strings in a file BASH
body: <p>I know some ppl asked the same question but I can't get any result,
  here is my text:</p>
  
  <pre><code>&lt;html&gt;
  &lt;head&gt;
  &lt;title&gt;emdee five for life&lt;/title&gt;
  &lt;/head&gt;
  &lt;body style="background-color:powderblue;"&gt;
  &lt;h1 align='center'&gt;MD5 encrypt this string&lt;/h1&gt;&lt;h3 align='center'&gt;PeKPATbxnupBGgWTIg5B&lt;/h3&gt;&lt;center&gt;&lt;form action="" method="post"&gt;
  &lt;input type="text" name="hash" placeholder="MD5" align='center'&gt;&lt;/input&gt;
  &lt;/br&gt;
  &lt;input type="submit" value="Submit"&gt;&lt;/input&gt;
  &lt;/form&gt;&lt;/center&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>I would like to extract 'PeKPATbxnupBGgWTIg5B' from it.
  I'm doing <code>sed -n "/^h3 align ='center'&gt;$/,/^&lt;h3$/p" thefile</code> but it does not return anything.
  Please help me :(</p>