#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

my $group   = shift;
my $gid     = getgrnam $group;
my @members = split ' ', (getgrgid $gid)[-1];

say "<$_>" for @members;

while (my ($pwnam, $group_id) = (getpwent)[0, 3]) {
    say "[$pwnam]" if $group_id == $gid;
}