PTY.spawn attaches a psuedo-terminal device to the standard input.

console.rb

require 'pty'

PTY.spawn 'irb' do |output, input, pid|
  loop do sleep 1
    input.puts 'puts :Wootz!'
    puts output.gets
  end
end

__END__

irb(main):001:0> puts :Wootz!
Wootz!
=> nil
irb(main):002:0> puts :Wootz!
Wootz!
=> nil
irb(main):003:0> puts :Wootz!
Wootz!
^Cconsole.rb:4:in `sleep': Interrupt
        from console.rb:4:in `block (2 levels) in <main>'
        from console.rb:4:in `loop'
        from console.rb:4:in `block in <main>'
        from console.rb:3:in `spawn'