I am at my wit's end, so please tell me where I am being stupid. Given a directory of files, I am trying to create the following multi-level hash.

my %o = (
  $yyyy => {$mm => {$dd => ['file_1'..'file_n']}}
);
[download]

Here is my code for doing so

use strict;
use File::Find;
use Fcntl;                          # to get 'em constants
use MLDBM qw(DB_File Storable);

our $dir = '/home/punkish/stuff';
our $db = '/home/punkish/data/files_by_dates.bdb';
our %o;

createDatesDb();

sub createDatesDb {

  # delete existing db, and create a new one
  unlink "$db"; tie %o, 'MLDBM', "$db", O_CREAT|O_RDWR, 0640 or die $!
+;
  
  find(\&_buildDatesDb, ("$dir") );
  
  untie %o;
}

sub _buildDatesDb {

    if (-f $_) {
    
      my @t = localtime( (stat("$_"))[9] );
      my $yyyy = $t[5] + 1900;
      my $mm  = sprintf("%02d", $t[4] + 1);
      my $dd  = sprintf("%02d", $t[3]);
      
      if (exists $o{$yyyy}) {
        if (exists $o{$yyyy}->{$mm}) {
        
          # year, month, and day exist, so push the file 
          # into the day's array
          if (exists $o{$yyyy}->{$mm}->{$dd}) {
            my $aref = $o{$yyyy}->{$mm}->{$dd};
            push(@$aref, $_);
          }
          
          # year exists, and month exists, but day doesn't yet exist,
          # so add it and all other info
          else {
            $o{$yyyy}{$mm}{$dd} = [$_];
          }
        }
        
        # year exists, but month doesn't yet exist,
        # so add it and all other info
        else {
          $o{$yyyy}{$mm} = {$dd => [$_]};
        }
      }
      
      # year doesn't yet exist, so add it and all other info
      else {
        $o{$yyyy} = {$mm => {$dd => [$_]}};
      }
    }
    
}
[download]

Pretty, simple. Except, it doesn't work, and I can't figure out why. If I Dumper \%o, I get the entire structure only one level deep. That is, I get all the years, but for each year, I get only one month, and for each month, I get only one day, and for each day, I get only one file in the array.

Here is the kicker. If I don't tie the hash, that is, I comment the unlink ..; tie ..; untie ..; lines in createDatesDb then Dumper \%o the untied hash, it shows up just the way I want it... that is, the hash is populated with all the files. Obviously, my logic is working, but the tie-ing is not.

What am I overlooking?