class Rails::Generators::Base

def self.add_shebang_option!


default value plus an instance helper method called shebang.
Small macro to add ruby as an option to the generator with proper 
def self.add_shebang_option!
  class_option :ruby, :type => :string, :aliases => "-r", :default => Thor::Util.ruby_command,
                      :desc => "Path to the Ruby binary of your choice", :banner => "PATH"
  no_tasks {
    define_method :shebang do
      @shebang ||= begin
        command = if options[:ruby] == Thor::Util.ruby_command
          "/usr/bin/env #{File.basename(Thor::Util.ruby_command)}"
        else
          options[:ruby]
        end
        "#!#{command}"
      end
    end
  }
end