#!/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:
my %two = %one;
# 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{$_}->[1]\tWhy???"}
say '%two:';
for(sort keys %two){say "$_\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	two	Why???
#b	3	two	Why???
#c	5	two	Why???
#%two:
#a	1	two
#b	3	two
#c	5	two