What is the best way to find username running your script?

[dr.jekyllandme]

Hello, I am writing a script that will find which user is executing the script. I found 3 different ways to do this:

#!usr/bin/perl

use strict;
use warnings;

my $logname = $ENV{ LOGNAME };
print "\$logname = $logname\n";

my $user = $ENV{ USER };
print "\$user = $user\n";

my $pwuid = getpwuid( $< );
print "\$pwuid = $pwuid\n";

I noticed that for $ENV{ LOGNAME } and $ENV{ USER }, I can changes the variable value using setenv in csh and export in bash. But getpwuid's value always gives me the correct value. So should I go with getpwuid to get the correct user that is calling the script? Is there a better way? Thank you.