LUA programming, ESP8266 NODEMCU Serial communication

I am trying to send data through the serial port of the EW8266 12E NODE MCU dev kit to the arduino serial port.

I am having a hard time finding an example of the syntax used and I tried to use serial.print () via arduino to send data and it works, but I'm not sure how to do it in Lua.

Any help is appreciated

I can get SSID and arduino password

INIT.lua

SSID = "XXXX"
Password = "XXXX"
wifi.setmode(wifi.STATION)
wifi.sta.config(SSID,Password) -- Replace with your AP Name and security key.
wifi.sta.connect()
tmr.alarm(1, 1000, 1, function() 
if wifi.sta.getip()== nil then 
print("Obtaining IP...") 
else 
tmr.stop(1)
print("Got IP. "..wifi.sta.getip())
dofile("LED_on_off.lua")

end

end)

      

        
        
        
      

    

LED_ON_OFF LUA

print(wifi.sta.getip())

led2 = 4
gpio.mode(led1, gpio.OUTPUT)
gpio.mode(led2, gpio.OUTPUT)
srv=net.createServer(net.TCP)
srv:listen(80,function(conn)
    conn:on("receive", function(client,request)
        local buf = "";
        local _, _, method, path, vars = string.find(request, "([A-Z]+) (.+)?(.+) HTTP");
        if(method == nil)then
            _, _, method, path = string.find(request, "([A-Z]+) (.+) HTTP");
        end
        local _GET = {}
        if (vars ~= nil)then
            for k, v in string.gmatch(vars, "(%w+)=(%w+)&*") do
                _GET[k] = v
            end
        end
        buf = buf.."<h1> ESP8266 Web Server</h1>";

        buf = buf.."<p>GPIO2 <a href=\"?pin=ON2\"><button>ON</button></a>&nbsp;<a href=\"?pin=OFF2\"><button>OFF</button></a></p>";
        local _on,_off = "",""
        if(_GET.pin == "OFF2")then
              gpio.write(led2, gpio.HIGH);
        elseif(_GET.pin == "ON2")then

**********Here i would like to send data ot arduini that pin is swithced oN ************

              gpio.write(led2, gpio.LOW);
        end
        client:send(buf);
        client:close();
        collectgarbage();
    end)
end)