harvest_receiver.lua

rednet.open("right")

while true do
    local id, msg = rednet.receive()

    if id~=13 and id~=8 then
        rednet.send(id, "Command refused, unauthorized ID")
        msg="refused"
    end

    if msg=="harvest" then
        shell.run("harvest")
        rednet.send("Harvesting...")
    else
        rednet.send("Unknown or refused command")
    end
end

rednet.close("right")