title: Regex: extract numbers between text
body: <p>currently I'm using such regex <code>"(\d{4}\b)"</code> in order to extract the numbers.
  Test string "test 125456 b", so the extract result is "5456".</p>
  
  <p>I wish to get the same result "5456" under the string "test125456b".</p>
  
  <p>I tried to use following regex </p>
  
  <pre><code>((?&lt;!\d)(\d{4})(?!\d))
  </code></pre>
  
  <p>but it works if only 4 digits (not more) are noted between letters.</p>
  
  <p>So, the aim is:</p>
  
  <ul>
  <li>extract only digits from the text</li>
  <li>extract only specific number of digits In this case 4) even in the text is given more</li>
  <li>digits (in this case 4) should be extracted backwards</li>
  </ul>