open LASTLOG, "/var/log/lastlog" or die; # location may vary
my $struct_lastlog = "L a8 a256"; # see "man lastlog" for struct sizes
my $size = length pack $struct_lastlog, 0, "", "";

while (my($user, $pwd, $uid) = getpwent) {
  next unless seek LASTLOG, $size * $uid, 0;
  next unless read(LASTLOG, my $buf, $size) == $size;
  my ($time, $line, $host) = unpack $struct_lastlog, $buf;
  s/\0*$// for $line, $host; # trim NULs
  next unless $time;
  printf "%8s %5d %30s %8s %s\n", $user, $uid, scalar localtime $time, $line, $host;
}