local bad_names = {
        con = true,
        prn = true,
        aux = true,
        nul = true,
}

for i=1,9 do
        bad_names["com" .. tostring(i)] = true
        bad_names["lpt" .. tostring(i)] = true
end

local bad_characters = { "<", ">", ":", "\"", "/", "\\", "|", "?", "*" }

local function has_bad_character(name)
        for _, char in ipairs(bad_characters) do
                if name:find(char, 1, true) then
                        return true
                end
        end
        return false
end

local function is_bad_name(name)
        return bad_names[string.lower(name)] or has_bad_character(name)
end

minetest.register_on_prejoinplayer(function(name)
        if is_bad_name(name) then
                return "No meme names allowed"
        end
end)