Convert CSS URI values

convert_css_uri.rb

# Parse CSS URI values according to http://www.w3.org/TR/CSS21/syndata.html#uri
URI_PATTERN = /
  url\(         # 'url('
  [ \t\n\r\f]*  # optional white space
  (
    # double quoted URI
    (
      (?<quote>")             # an optional double quote
      (?<str>([^"\\]|\\.)*?)  # URI
      "
    )
    # or single quoted
    | (
      (?<quote>')             # an optional single quote
      (?<str>([^'\\]|\\.)*?)  # URI
      '
    )
    # or unquoted
    | (?<str>
      ([^() \t\n\r\f'"\\]|\\.)*  # parentheses, white space characters,
                                 # single quotes, and double quotes must be
                                 # escaped
    )
  )
  [ \t\n\r\f]*  # optional white space
  \)            # ')'
/x

data = 'load css file here'

data.gsub! URI_PATTERN do |match|
  # TODO do something here
  puts $~[:quote], $~[:str]
  'url([PUT SOMETHING HERE])'
end