This regex matches and shouldn't. Why is it?

Question

This regex:

^((https?|ftp)\:(\/\/)|(file\:\/{2,3}))?(((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3} (25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))|(((([a-zA-Z0-9]+)(\.)?)+?)(\.)([a-z]{2} |com|org|net|gov|mil|biz|info|mobi|name|aero|jobs|museum))([a-zA-Z0-9\?\=\&\%\/]*)?$

Formatted for readability:

^( # Begin regex / begin address clause
  (https?|ftp)\:(\/\/)|(file\:\/{2,3}))? # protocol
  ( # container for two address formats, more to come later
   ((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}
   (25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?) # match IP addresses
  )|( # delimiter for address formats
   ((([a-zA-Z0-9]+)(\.)?)+?) # match domains and any number of subdomains
   (\.) #dot for .com
   ([a-z]{2}|com|org|net|gov|mil|biz|info|mobi|name|aero|jobs|museum) #TLD clause
  ) # end address clause
([a-zA-Z0-9\?\=\&\%\/]*)? # querystring support, will pretty this up later
$

is matching:

www.google

and shouldn't be. This is one of my "fail" test cases. I have declared the TLD portion of the URL to be mandatory when matching on alpha instead of on IP, and "google" doesn't fit into the "[a-z]{2}" clause.

Keep in mind I will fix the following issues seperately - this question is about why it matches www.google and shouldn't.

• Querystring needs to support proper formats only, currently accepts any combination of querystring characters
• Several protocols not supported, though the scope of my requirements may not include them
• uncommon TLDs with 3 characters not included
• Probably matches http://www.google..com - will check for consecutive dots
• Doesn't support decimal IP address formats

What's wrong with my regex?

edit: See also a previous problem with an earlier version of this regex on a different test case: How can I make this regex match correctly?

edit2: Fixed - The corrected regex (as asked) is:

^((https?|ftp)\:(\/\/)|(file\:\/{2,3}))?(((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3} (25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))|(((([a-zA-Z0-9]+)(\.)?)+?)(\.)([a-z]{2}|com|org|net|gov|mil|biz|info|mobi|name|aero|jobs|museum))([\/][\/a-zA-Z0-9\.]*)*?([\/]?[\?][a-zA-Z0-9\=\&\%\/]*)?$

Answer 1

"google" might not fit in [a-z]{2}, but it does fit in [a-z]{2}([a-zA-Z0-9\?\=\&\%\/]*)? - you forgot to require a / after the TLD if the URL extends beyond the domain. So it's interpreting it with "www.go" as the domain and then "ogle" following it, with no slash in between. You can fix it by adding a [?/] to the front of that last group to require one of those two symbols between the TLD and any further portion of the URL.