planbnet

(?x)
\b
(                       # Capture 1: entire matched URL
  (?:
    [\w-]+:                 # URL protocol and colon
    (?:
      /{1,3}                    # 1-3 slashes
      |                         # or
      [[:alpha:][:digit:]]      # Single letter or digit
                                # (Try not to match, say "URI::Escape")