Phone number regular expression

gistfile1.rb

  # A phone number consists of up to six groups of digits which may or may not
  # be separated from each other using one of the separater characters dot ".",
  # dash "-" or space " ". The six groups are:
  # (1) International country code, which is a one to four digit number
  #     prefixed by a plus sign "+". The plus sign is optional if - and only if -
  #     the country code is immediately followed by a separator char.
  #     The whole country code group is optional.
  # (2) Area code, which is a one to three digit number enclosed in parenthesis
  #     "()". The parenthesis are optional if - and only if - the area code is
  #     immediately followed by a separator char.
  #     The whole area code group is optional.
  # (3-6) Two to four groups of three to five digits each, optionally seprated
  #     by a single separator char.
  #
  PHONE_REGEX = %r{
    (?<! [\w\$-] )   # negative look-behind: number is not immediately
                     # preceeded by a word character, "$" or "-"
    (?: \+ \d{1,4}    | \+? \d{1,4}     [\ \.\-] )?                    # (1) international country code
    (?: \( \d{1,3} \) | \(  \d{1,3} \)  [\ \.\-] | \d{1,3} [\ \.\-] )? # (2) area code
    (?: \d{3,5} [\ \.\-]? ){1,3} \d{3,5}                               # (3-6) local number
    \b               # word boundary
  }x