using tie on hash of hashes

gnu@perl has asked for the wisdom of the Perl Monks concerning the following question:

I have been using a text file for a config file. I now wish to put this into a dbm file on disk and tie a hash to it. This will take the loading of the text file into a hash of hashes out of my program. The problem I seem to have (I think) is that you cannot tie a file on disk to a hash of hashes. It seems that the multi-dimensional nature of the HoH prevents. this. Any ideas? P.S. Please forgive me for the dual post. I first posted this in the Q&A and then realized I should have posted it here.

use strict;
use Fcntl;
use NDBM_File;
my $configFile    = "$ENV{HOME}/\.logmConfig";
my %prefs;
tie %prefs, "NDBM_File", "$configFile", O_RDWR|O_CREAT, 0644 or die "C
+annot tie to $configFile:\n$!\n";
      %prefs = (
         'hopper.uslec.net' => {
          '/u20/gvc/log/log.log'  => 50,
       '/u20/gvc/log/log2.log' => 12,
      },
      );
print_hash();
untie %prefs;
sub print_hash{
  my ($server,$log,$lines);
  foreach $server (keys %prefs) {
    print   "$server\n";
    foreach $log ( keys %{ $prefs{$server} } ) {
      print "  $log\n";
      print "     $prefs{$server}{$log}\n";
    }
  }
};
[download]

Comment on using tie on hash of hashes Download Code

Replies are listed 'Best First'.
Re: using tie on hash of hashes by Anonymous Monk on Aug 16, 2002 at 16:58 UTC
The MLDBM module will give you the capability you desire.	[reply]
Re: Re: using tie on hash of hashes by rob_au (Abbot) on Aug 17, 2002 at 14:57 UTC
++Anonymous Monk ... One important thing to note about tied hashes with MLDBM though is that the value of a hash should be copied to a temporary variable prior to its manipulation. From the BUGS section of the module POD ... `$mldb{key}{subkey}[3] = 'stuff'; # won't work tmp = $mldb{key}; # retrieve value $tmp->{subkey}[3] = 'stuff'; $mldb{key} = $tmp; # store value` [download] This limitation exists as a result of the Perl TIEHASH interface having no support for multidimensional ties. I wrote about this topic in a more general way in The importance of context in debugging.	[reply] [d/l]