itworks.rb

# Added small readability tweak
# input/output instead of pull/push

class TwoWayPipe
  attr_reader :input, :output
  def initialize
    @input, @output = IO.pipe
  end
end

class PipeProcess
  def self.start(command, last_pipe = TwoWayPipe.new, original_pipe = last_pipe)
    new(command, last_pipe, original_pipe)
  end

  attr_reader :original_pipe
  def initialize(command, last_pipe, original_pipe)
    @original_pipe = original_pipe
    pipe = TwoWayPipe.new

    fork do
      pipe.output.close

      STDOUT.reopen(last_pipe.output)
      STDIN.reopen(pipe.input)
      exec command
    end

    @pipe = pipe
  end

  def read
    @original_pipe.output.close
    @original_pipe.input.read
  end

  def pipe(command)
    self.class.start(command, @pipe, @original_pipe).tap do
      @pipe.output.close
    end
  end
end

class ReversePipeProcess
  def initialize(command, last_process = nil)
    @command, @last_process = command, last_process
  end

  def pipe(command)
    self.class.new(command, self)
  end

  def commands
    commands = []
    commands << @command
    commands.concat(@last_process.commands) if @last_process
    commands
  end
  
  def read
    list = commands
    first = PipeProcess.start(list.shift)
    list.inject(first) {|process, command| process.pipe(command) }.read
  end
end

module Kernel
  def pipe(command)
    ReversePipeProcess.new(command)
  end
end

puts pipe("ls").pipe("grep Adium").pipe("grep 'Update 1'").read