Re: Deleting hash entry

[Aragorn]

First of all, the notation %hash = { ... is wrong. You either assign a hash with %hash = ( ... or a hash reference with $hash = { .... Watch those parentheses and curly braces. See perlreftut and perlref for more information.

As for deleting:

#!/usr/bin/perl

use Data::Dumper;

$hash = {
    abc => {
        'def' => 1,
    },
    ghi => {
        jkl => 1,
        mno => 1,
    },
};
print Dumper(\$hash);
delete($hash->{abc}->{def});
print Dumper(\$hash);
__END__
$VAR1 = \{
            'abc' => {
                       'def' => 1
                     },
            'ghi' => {
                       'mno' => 1,
                       'jkl' => 1
                     }
          };
$VAR1 = \{
            'abc' => {},
            'ghi' => {
                       'mno' => 1,
                       'jkl' => 1
                     }
          };

The second question: I don't know :-). Having an undefined hash value is perfectly valid, so the upper level is not automatically deleted when the lower level becomes undefined. You could add a statement like delete $hash->{$key} if not keys %{$hash->{$key}}. This deletes the key only if the hash it references is empty.

Arjen