title: What does [[ $strin = *[!0-9]* ]] mean in bash?
body: <p>I'm learning bash, in particular regular expressions and I found this in my book:</p>
  
  <pre><code>read strin
  
  if [[ $strin = *[!0-9]* ]]; then
  
     echo "error"
  
  else
     echo "success"
  
  fi
  </code></pre>
  
  <p>My problem is that I don't understand what this regular expression means, in particular I don't understand the '!' in the range. </p>