my $sep = '##';
my $sep_len = length($sep);

my $last_pos = index($str, $sep);

for (;;) {
  my $pos = index($str, '##', $last_pos + $sep_len);

  my $rec;
  if ($pos < 0) {
     $rec = substr($str, $last_pos);
     last if not length $rec;
  } else {
     $rec = substr($str, $last_pos, $pos-$last_pos);
     $last_pos = $pos;
  }

  my $rid = substr($rec, 19, 10);
  print "$rid: " . ($keeplist{$rid} ? 'y' : 'n') . "\n";

}