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use strict;
use warnings;
...
my @values = Dive ( \%h, 'key3', 'key4' );
printf "key3-key4 %s exist\n", @values ? 'does' : 'does not';
print Dumper( \%h );

Testing with exists
key1 does not exist
...
$VAR1 = {
          'key1' => {}
        };