Since it was hard won here is the same thing for HP-UX:

$template = "A8 A4 A12 l s s s s l A16 l";

# determine the size of a record
$recordsize = length(pack($template,(  )));

while (read(WTMP,$record,$recordsize)) {
  ($ut_user, $ut_id, $ut_line, $ut_pid, $ut_type, $ut_e_termination, $
+ut_e_exit, $ut_reserved1, $ut_time, $ut_host, $ut_addr) = unpack($tem
+plate,$record);
}
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Of course the portable way to do this is with one of User::Utmp or Sys::Utmp :)