#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my %hash = ('key' => 'value');
print Dumper \%hash;

#prints:
#$VAR1 = {
#          'key' => 'value'
#        };

print "defined\n" if defined $hash{abc}{xyz}; # will create new keys
print "defined\n" if defined ($hash{x}) and defined ($hash{x}{y}); # added: won't create new keys
print "exists\n"  if exists  ($hash{x}) and exists($hash{x}{y});   # added: won't create new keys
print "exists\n"  if exists $hash{x1}{x2};   # added: will create new keys
print "defined\n" if defined $hash{x3};      # added: no new key

print Dumper \%hash;

__END__
#prints:
# The "abc" key is created due to the check for defined of 2nd dimension
# exists will also create new intermediate keys

$VAR1 = {
          'key' => 'value',
          'abc' => {},
          'x1' => {}
        };