gistfile1.txt

scheme:[//[user:password@]host[:port]][/]path[?query][#fragment]

(file|ftp|https|http|irc|mailto):\/\/((\w+(:\w+)?@)?\w(\w\.?)*(:\d{1,5})?\/?)?(\w(\w+\/)*)?(#\w+)?

---

scheme = (file|ftp|https|http|irc|mailto):\/\/
   
          optional username followed by optional :password. Username and password ar alphanumeric
          |
          v
user = (\w+(:\w+)?@)?

        an alphanumeric char followed by (any number of characters optionally followed by a period)
        |
        v
host = \w(\w\.?)*
 
        optional port, 1 to 5 digits
        |
        v
port = (:\d{1,5})?

        optional (alphanumeric char followed by any number of alphanumeric characters interspereced with /)
        |
        v
path = (\w(\w+\/)*)?

        optional characters following ?. As long as those characters are not #
        |
        v
query = (\?[^#]+)?


        optional anything following #
        |
        v
query = (#.+)?


----

combine together. The entirety of (user host port) is optional

  scheme
  (user
  host
  port)?
  path
  query
  fragment