Nip === This gem provides the Nip class to check the NIP number. NIP (Numer Identyfikacji Podatkowej) is the Polish Tax Identification Number. More information (in Polish language): http://pl.wikipedia.org/wiki/NIP If you are looking for the Nip as a plugin: http://github.com/macuk/nip-plugin Installation ============ gem install nip Example ======= Standalone class: nip = Nip.new('845-167-08-82') nip.valid? # true nip.to_s # '8451670882' ActiveRecord: class Company < ActiveRecord::Base validate :check_nip private def check_nip n = Nip.new(nip) errors[:nip] << 'Invalid NIP number' unless n.valid? end end Copyright (c) 2010 Piotr Macuk, released under the MIT license