shell-like pipeline in Ruby DSL

pipeline.rb

#!/usr/bin/env ruby

module PipeOperator
  refine Array do
    def |(x)
      PipeLine.new(self) | x
    end
  end
end

class PipeLine
  def initialize(cmd)
    @cmds = [cmd]
  end

  def |(cmd)
    @cmds << cmd
    self
  end

  def execute
    cmds = @cmds

    # copied from http://tmtms.hatenablog.com/entry/2013/10/09/sheru
    pipes = Array.new(cmds.count-1){IO.pipe}
    pipes = [nil, pipes.flatten.reverse, nil].flatten
    cmds.each do |cmd, *args|
      r, w = pipes.shift 2
      pid = Process.fork do
        STDIN.reopen r if r
        STDOUT.reopen w if w
        Process.exec [cmd, cmd], *args
      end
      r.close if r
      w.close if w
    end
    Process.waitall
  end

  def self.run
    yield.execute
  end
end

if __FILE__ == $0
  using PipeOperator

  PipeLine::run { ['yes', 'Yo!'] | ['nl'] | ['head', '-n', '10'] }
end