Rednet Repeater

local receiverId;
local arg={...};

local function help()
    print("This program turns a PC into a message repeater. The PC resends the messages it receives to another PC (which may itself be a repeater).");
    print("To use this program put a wireless modem on the left side of the computer.");
end

if (#arg==0)
then
    printError("You have to specify an argument.");
    print("\nArguments:");
    print("help: Display an help guide.");
    print("id: Get the id of this computer to use with rednet.");
    print("start id: Start the program. \"id\" is the id of the receiver.");
    return;
else
    if (arg[1]=="id")
    then
        print("Receiver id: "..os.getComputerID());
        return;
    elseif (arg[1]=="help")
    then
        help();
        return;
    elseif (arg[1]=="start")
    then
        if (arg[2]~=nil)
        then

            receiverId=tonumber(arg[2]);

            if (receiverId==nil)
            then
                printError("\"id\" must be a number!");
                return;
            end
        else
            printError("You have to specify the id of the receiver computer!");
            return;
        end
    else
        printError("Wrong argument!");
        return;
    end
end

rednet.open("left");
term.clear();
term.setCursorPos(1, 1);


while(true)
do
    senderId, msg, protocol=rednet.receive();

    term.clear();
    term.setCursorPos(1, 1);

    if (protocol==nil)
    then
        protocol="No protocol";
    end

    print("Message received:");
    print("\nSender ID: "..senderId);
    print("Message: "..msg);
    print("Protocol: "..protocol);


    rednet.send(receiverId, msg);
end