I just learned yesterday about the getlogin function built into Perl, which works under both, Unix and Windows:

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";
[download]

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

So the above code should be used instead of what you have now.