Monitor.lua

monitor = peripheral.wrap("left")
term.redirect(monitor)
monitor.setTextScale(2)
term.clear()
modem = peripheral.wrap("back")

chan = 36602
modem.open(chan)

local function func1 (l)
    local w, h = term.getSize()
    l = #l
    xpos = w/2 - l/2 + 1
    return xpos
end

while true do
    event, modemSide, senderChannel, replyChannel, message, distance = os.pullEvent("modem_message")

    if (senderChannel == 36602) then
        message = "Pre Text : " .. message
        term.clear()
        term.setCursorPos(func1(message), 2)
        print(message)
    end
end