dup2 を自分で使う場合

pty.rb

require 'fiddle/import'
module Dupper
  extend Fiddle::Importer
  dlload 'libc.so.6'
  extern 'int dup2(int oldfd, int newfd);'
end

require 'pty'

master, tty = PTY.open

pid = fork do
  Dupper.dup2(tty.fileno, 0)
  Dupper.dup2(tty.fileno, 1)
  Dupper.dup2(tty.fileno, 2)
  exec 'wc'
end
tty.close
master.puts "hello"
master.gets
master.puts "world"
master.gets
master.puts "\u{04}"
master.gets
begin
  while l = master.readline
    puts "PTY: " + l
  end
rescue Errno::EIO => e
end
p Process.waitpid2(pid)