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

my %hash = (1 => {1 => 1});
my $key = '1';

print "$hash{'$key'}{'$key'}\n";
print Dumper(\%hash);
##</code><code>##

Use of uninitialized value in concatenation (.) or string at junk.pl line 9.

$VAR1 = {
          '1' => {
                   '1' => 1
                 },
          '$key' => {}
        };