gistfile1.txt

# Ip.valid? '1.2.3.4'
module Ip
  def self.pattern
    @pattern ||= {
      # pattern to match a single ip address or cidr
      :ip => %r{^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})(?:\/\d{1,2})?$},
    }
  end

  def self.valid? address
    address.match(pattern[:ip]).captures.all? do |octet|
      octet.to_i < 256
    end rescue false
  end
end