Dear Perl Monks,
this is my first post, so sorry if I am wrong in some way.
I am working with multidimensional hashes, and I get an output which seems to me quite weird.
In particular:
- I create a multidimensional hash;
- I create a copy of this hash;
- I modify that copy.
When I print, it seems that both hashes were modified, and I do not understand why. With monodimensional hashes, everything is normal instead.
Please consider the following script and the output I receive:

#!/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
[download]

Thanks for any explanation you could give me!
Tommaso

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