use Data::Dumper;
no strict;
%hash = ( a => 'x123' );
$hash{a}{b} = 'data';
print Dumper \%hash;

##</code><code>##

$VAR1 = {
          'a' => 'x123'
        };

##</code><code>##

print Dumper \%hash, \%x123;

##</code><code>##

Name "main::x123" used only once: possible typo at Z:\test.pl line 6.
$VAR1 = {
          'a' => 'x123'
        };
$VAR2 = {
          'b' => 'data'
        };