Sidekiq, Upstart, and Capistrano

deploy.rb

namespace :deploy do
  namespace :sidekiq do
    desc 'Replace upstart config for sidekiq-workers'
    task :upstart_config do
      data = %Q{
        start on runlevel [2345]
        stop on runlevel [!2345]
        respawn

        exec su - #{user} -c 'cd #{release_path}; export RAILS_ENV=#{stage};  bundle exec sidekiq -q default,1 -c 4 -pid #{release_path}/tmp/pids/sidekiq.pid >> #{release_path}/log/sidekiq.log 2>&1'
      }
      source_path = release_path + '/config/sidekiq-workers.conf'
      put data, source_path
      sudo "cp -f #{source_path} /etc/init/sidekiq-workers.conf"
    end

    desc "Restart sidekiq"
    task :restart do
      sudo "service sidekiq-workers stop; /bin/true"
      sudo "service sidekiq-workers start"
    end
  end
end

where and how do you define stage variable?