IsPlayerInACL

This code will return true, if the given player is in the given ACL group. If the given player isn't in the given ACL group, it will return false.

Code

function isPlayerInACL(player,acl)
	local account = getAccountName(getPlayerAccount(player))
	if(isObjectInACLGroup("user."..account,aclGetGroup(acl))) then
		return true
	else
		return false
	end
end

Usage:

function playerLogin()
	if (isPlayerInACL(source,"Admin")==true) then
		outputChatBox(getPlayerName(source).." has logged in!", root, 0, 255, 0)
	end
end
addEventHandler("onPlayerLogin",root,playerLogin)

Code by xXMADEXx