s/([A-Z0-9]{5,})/$seenit{$1}++/egi while <>;

## Sorted by name
for (sort keys %seenit) {
  print "$_: $seenit{$_}\n";
}

## Sorted by freuency, then by name:
for (sort {$seenit{$a} <=> $seenit{$b} or $a cmp $b} keys %seenit) {
  print "$_: $seenit{$_}\n";
}