title: How to extract a value from a string using regex and a shell?
body: <p>I am in shell and I have this string: <code>12 BBQ ,45 rofl, 89 lol</code></p>
  
  <p>Using the regexp: <code>\d+ (?=rofl)</code>, I want <code>45</code> as a result.</p>
  
  <p>Is it correct to use regex to extract data from a string? The best I have done is to highlight the value in some of the online regex editor. Most of the time it remove the value from my string.</p>
  
  <p>I am investigating <code>expr</code>, but all I get is syntax errors.</p>
  
  <p>How can I manage to extract 45 in a shell script?</p>