function adminchat(p,_,...)
local message = table.concat({...}, " ")
local account = getPlayerAccount (p)
if isGuestAccount(account) then return end
if not isObjectInACLGroup ( "user." .. getAccountName(account), aclGetGroup("Admin") ) then return end
local r, g, b = getPlayerNametagColor(source)
outputChatBox ( "[Admin]"..getPlayerName ( source ) .. ":#ffffff " .. message, root, r, g, b, true )
end
addEventHandler("onPlayerJoin", root, function()
bindKey(source, "u", "down", "chatbox", "a")
end
)
addCommandHandler("a", adminchat)
Please learn from the code, because i spoon fed this.
Press U ingame to open the chat.