Wither Redstone Receive Program

rednet.close("left")
rednet.open("left")

local white = 1
local blue = 2048
local green 8192

while true do
  os.pullEvent("redstone")
  local signal = rs.getBundledInput("back")
  if signal == white then
    rednet.send(39, "BUILD", "UPDATE")
  elseif signal == blue
    rednet.send(39, "REDST", "UPDATE")
  elseif signal == green
    rednet.send(39, "END", "UPDATE")
  end

  sleep(1)
end