title: Regex: Match only if string A is found and string B is not
body: <p>I'm trying to write a regular expression that will essentially return true if string A is found and string B is not found.</p>
  
  <p>To be more specific, I'm looking for any file on my server which has the text 'base64_decode' in it, but not 'copyright'.</p>
  
  <p>Thanks!</p>