use strict;
use warnings;
use Data::Dumper;

my %hash_data = ();

my $key1 = "a";
my $key2 = "1";
my $key3 = "B";
my $key4 = "_";


if (exists $hash_data{$key1}{$key2}{$key3}{$key4}) {
    print "exists\n";
} else {
    print "DOES NOT EXIST\n"
}

print "-----\n";
print Dumper (\%hash_data);

##</code><code>##

DOES NOT EXIST
-----
$VAR1 = {
          'a' => {
                   '1' => {
                            'B' => {}
                          }
                 }
        };