sub _exists {
    my ($hash, @keys, @exists) = @_;

    if (exists $hash->{$keys[0]}) {
        my $key = shift @keys;
        push @exists, 1, _exists($hash->{$key}, @keys);
    }

    return @exists;
}

sub exists_keys {
    return &_exists == $#_ ? 1 : ();
}

my %hash;
#$hash{a}{b}{c} = undef;

if (exists_keys(\%hash, qw(a b c))) {
    print "Exists.\n";
}
else {
    print "Doesn't exists.\n";
}