title: awk extract number from field
body: <p>I would like to extract the numbers a field contains.</p>
  
  <p>For example filed <code>$5</code> looks like <code>[u8789]</code> I would need <code>8789</code>.</p>
  
  <p>I already know it can be done with <code>echo "[u8789]"|awk -F'[^0-9]*' '$0=$2'</code></p>
  
  <p>But I need the same in an awk script, and I have not found out how to get the expected result without calling awk from shell.</p>
  
  <p>thx</p>