What's the best way to deep copy a hash of hashes in Perl? [duplicate]

Question

Possible Duplicate:
What's the best way to make a deep copy of a data structure in Perl?

Before I start coding this myself and reinventing the wheel, how do you copy a hash of hashes without duplicating the hashrefs?

I'm reading a hash of hash of hashes via Config::General. i.e., the data structure is:

my %config = ( group => { item1 => { foo => 'value',                                      bar => 'value',                                    },                           item2 => { foo => 'value',                                      bar => 'value',                                    },                           item3 => { foo => 'value',                                      bar => 'value',                                    },                         },              ); 

I then pull my group from the config by dereferencing it and change the contents at runtime prior to rewriting the config file:

my %group = %{$config{'group'}}; 

The problem is that I need to check to see if changes were made and make associated changes to the system's file structure. I can't do this by checking:

if ($group{'item1'}{'foo'} ne $config{'group'}{'item1'}{'foo'}) {     ### Stuff! } 

as $group{'item1'} and $config{'group'}{'item1'} are both the exact same hashref.

Now while it should be trivial to simply re-parse the config file, and compare the parsed copy from the disk against the edited version just before saving to disk, I'm sure there's a way to to a nested dereference of a complex data structure, copying the contents of the hash refs and not simply copying the references themselves. A cursory examination on CPAN doesn't turn anything up. What am I missing?

Benchmark

Got my answer:

#!/usr/bin/perl  use Benchmark qw(:all) ; use Storable qw(dclone); use Clone qw(clone);  my %config = ( group => { item1 => { foo => 'value',                                      bar => 'value',                                    },                           item2 => { foo => 'value',                                      bar => 'value',                                    },                           item3 => { foo => 'value',                                      bar => 'value',                                    },                         },              );  my $ref = $config{'group'};  timethese(100000, {   'Clone' => sub { my %group = %{ clone $ref }},   'Storable' => sub {  my %group = %{ dclone $ref }}, }); 

results in:

 Benchmark: timing 100000 iterations of Clone, Storable...    Clone:  2 wallclock secs ( 2.26 usr +  0.01 sys =  2.27 CPU) @ 44052.86/s (n=100000) Storable:  5 wallclock secs ( 4.71 usr +  0.02 sys =  4.73 CPU) @ 21141.65/s (n=100000) 

Answer 1

use Storable qw(dclone); $group2 = dclone(\%group);