A method to define rake file tasks which depend on multiple files which are concatenated after being processed with ERB

snippet.rb

module RakeExtensions
  def concat(*args, &block)
    t = Rake::FileTask.define_task(*args)
    out_file = t.name
    list = []
    yield list if block_given?
    t.enhance(list) do
      File.open(out_file, 'w+') do |f|
        f << list.map do |item|
          ERB.new(IO.read(File.expand_path(item)), nil, '%').result(binding)
        end * $/
      end
    end
  end
end

# usage:
#   concat some_file do |list|
#     list << "header"
#     list << "some_source_file"
#   end