gistfile1.rb

Ducklink::Decorator.configure do
    group do
        template 'http://affiliate.example.com?clickref={{reference}}&url={{url}}#campaign={{campaign}}'
        host 'buy.example.com', 'shop.example.com' do |context|
            set :campaign, 'campaign1'
            set :reference, context[:reference]
        end
        host 'another.com' do |context|
            set :campaign, 'campaign2'
            set :reference, context[:reference]
        end
    end
end