Best way to get IP from domain

[kingzooly]

I used nslookup

function GetIP(s_URL)
    local getip = io.popen("nslookup "..s_URL.." | find /i \"Address\"");
    local getipout = getip:read("*a");
    getip:close();
    getnum = String.Find(getipout, "Address", 2, true);
    getipout = String.Mid(getipout, getnum+9, -1);
    return getipout;
end

[kingzooly]

What is the best way to get the IP from a domain, I use dynamic IP address on a domain so at times it can change, so I need to resolve the domain address to a IP address. can it be done in Lua or a command line tool or do I have to use some online service?