proxying I/O from one script to another

main.rb

#!/usr/bin/env ruby

require 'open3'

puts 'party time'
output = ''
status = Open3.popen2e('./sub.rb') do |std_in, std_out_err, wait_thr|
  Thread.new do
    begin
      while out = std_out_err.readpartial(64)
        print(out); STDOUT.flush
        output += out
      end
    rescue EOFError
    end
    std_out_err.close
  end
  Thread.new do
    while input = STDIN.readpartial(64)
      output += input
      std_in.write(input)
    end
    std_in.close
  end
  wait_thr.value.exitstatus
end

puts "Output: #{output}"
puts "Status: #{status}"

sub.rb

#!/usr/bin/env ruby

# this is important!  I don't know of a way that it could be set
# from main.rb, e.g. if you only had control of main.rb and not sub.rb
STDOUT.sync = true

puts "it's a test!"
loop do
  print "gimme something (q to quit)> "
  x = gets.chomp
  puts "you gave me #{x}"
  exit if x == 'q'
end