my %users = ();
my %groups = ();

my $pfname = '/etc/passwd';
open(my $pfh, $pfname) || warn "Error reading $pfname: $!";
while (my $line = <$pfh>) {
  my ($name) = split(/:/, $line);
  $users{$name} = 1;
}
close $pfh;

my $gfname = '/etc/group';
open(my $gfh, $gfname) || warn "Error reading $gfname: $!";
while (my $line = <$gfh>) {
  my ($name) = split(/:/, $line);
  $groups{$name} = 1;
}
close $gfh;