#!/usr/bin/env perl
use Modern::Perl 2011;
use autodie;
# I create a multidimensional hash
my %one = ('a' => [1, 2],
           'b' => [3, 4],
           'c' => [5, 6]);
# I create a copy:
# wrong way:
#my %two = %one;
# right way:
my %two;
for(keys %one)
   {$two{$_}[0] = $one{$_}[0];
    $two{$_}[1] = $one{$_}[1]}
# I print them:
say "Before:\n\%one:";
for(sort keys %one){say "$_\t$one{$_}[0]\t$one{$_}[1]"}
say '%two:';
for(sort keys %two){say "$_\t$two{$_}[0]\t$two{$_}[1]"}
# Then I modify the copy:
for(sort keys %two){$two{$_}[1] = 'two'}
# And I print again:
say "After:\n\%one:";
for(sort keys %one){say "$_\t$one{$_}[0]\t$one{$_}[1]\tOk!!!"}
say '%two:';
for(sort keys %two){say "$_\t$two{$_}[0]\t$two{$_}[1]"}

# I receive this output:
#Before:
#%one:
#a	1	2
#b	3	4
#c	5	6
#%two:
#a	1	2
#b	3	4
#c	5	6
#After:
#%one:
#a	1	2	Ok!!!
#b	3	4	Ok!!!
#c	5	6	Ok!!!
#%two:
#a	1	two
#b	3	two
#c	5	two