arduino_ruby_serial_read.rb

require "serialport"

 #params for serial port
 port_str = "/dev/cu.usbmodem1411"  #may be different for you
 baud_rate = 9600
 data_bits = 8
 stop_bits = 1
 parity = SerialPort::NONE

 serial_port = SerialPort.new(port_str, baud_rate, data_bits, stop_bits, parity)

 #just read forever
 while true do
   while (i = serial_port.gets.chomp) do
     puts i
     sleep 0.5
   end
 end

 serial_port.close