Lightweight Databases

Ordered Hashes

     tie %hash, 'DB_File', $file, O_CREAT|O_RDWR, 0666, $DB_BTREE;

By default, the ordering is lexicographic:

     for (qw(red orange yellow green blue violet)) {
        $hash{$_} = length;
     }

     print join(" ", keys %hash), "\n";

     blue green orange red violet yellow

You may specify an alternative ordering:

     use DB_File;

     my $rev_btree = DB_File::BTREEINFO->new();
     $rev_btree->{compare} = 
       sub { 
         my ($a, $b) = @_; 
         reverse($a) cmp reverse($b) 
       };

     tie %hash, 'DB_File', $file, O_CREAT|O_RDWR, 0666, $rev_btree;

     red orange blue green violet yellow