sub make_hash {
  my %hash;

  # Do clever stuff to fill in values in hash

  return \%hash;
}

##</code><code>##

my $thisDataset = make_hash();

##</code><code>##

sub do_stuff_to_hash {
  foreach (keys %{$_[0]}) {
    # do something with each key
  }
}

do_something_with_hash($thisDataset);

##</code><code>##

$thisDataset{$curr_month};

##</code><code>##

$thisDataset->{$curr_month};