use DB_File;
$DB_BTREE->{compare} = sub { $_[1] cmp $_[0] };
tie my %h, 'DB_File', undef, O_RDWR|O_CREAT, 0666, $DB_BTREE
    or die "DB_File tie failed: $!";
%h = 'a' .. 'z';
print "$_ : $h{$_}\n" for keys %h;