use warnings;
use strict;

use User::pwent;
use User::grent;
use List::Util qw/any/;

my $u = $ENV{USER};
print " primary: ",
	getpwnam($u)->gid, "\n";
print "seconday: $_\n" for get_sec_grps($u);

sub get_sec_grps {
	my $user = shift;
	my @sec_grps;
	endgrent; # reset (?)
	while (my $g=getgrent) {
		push @sec_grps, $g->gid
			if any {$_ eq $user} @{$g->members};
	}
	endgrent;
	return @sec_grps;
}