getlogin
            This implements the C library function of the same name, which
            on most systems returns the current login from /etc/utmp, if
            any. If it returns the empty string, use "getpwuid".

                $login = getlogin || getpwuid($<) || "Kilroy";

            Do not consider "getlogin" for authentication: it is not as
            secure as "getpwuid".

            Portability issues: "getlogin" in perlport.