open5

gem install open5

and

require 'open5'
open5('command', 'opt') {|i, o, e, t|
  i.puts 'input!'
  p o.gets
  Process.kill 'KILL', t.pid
}

or

require 'open5'
i, o, e, t = open5('command', 'opt')

• open3 doesn't give the pid on ruby 1.8.
• open4 has different interface to open3 on ruby 1.9.
• tasks doesn't work on Windows because it uses fork.

open5 works both on ruby 1.8 and 1.9, and supports Windows! (Though I've never tested it on Windows yet.)

• open4

Tatsuhiro Ujihisa