This functiontakes elements in an array and builds them into keys for a hash:

#  Usage: UsesArrayElementsAsKeyElementsInHash( \%hash, $value, @array
+ )
use Carp;
sub UsesArrayElementsAsKeyElementsInHash
{
  my $hash = my $root = ( ref $_[0] ? shift : {} );
  my $value = shift;
  my $last = pop;

  for my $key ( @_ )
  {
    $hash = ( $hash->{$key} ||= {} );
    ref $hash or croak "key = $key\n";
  }
  $hash->{$last} = $value;
  return $root;
}
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