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 null, use "getpwuid".
 
                   $login = getlogin || getpwuid($<) || "Kilroy";

##</code><code>##

 perl -e 'print getlogin || getpwuid($<)'
lanx