title: Perl: Remove non-letter, non-number characters from string
body: <p>I have a Perl string that is only allowed to contain the letters A to Z (capital and lowercase), the numbers 0 to 9, and the "-" and "_" characters. I want to remove all non-matching characters from the string, leaving the rest untouched.</p>
  
  <p>So "Hell@_World" would become "Hell_World".</p>