Copying a hashref in Perl [duplicate]

Answer 1

Yes, assignment just copies the reference (like copying a pointer value in other languages). What you're looking for is called a "deep copy".

Storable::dclone seems to be one solution (perldoc Storable for more information).

Clone is another (perldoc clone); thanks to Zaid for mentioning this in a comment.

Answer 2

If it's just a hash and all you're looking for is a copy of it:

my $hashref = {data => "a"};

my %hash_copy = %{$hashref}; # Create a copy of the hash that $hashref points to
my $hashref_copy = \%hash_copy; # Ref to %hash_copy
$hashref_copy->{data} = "b";

print "$hashref->{data}\n"; # Outputs 'a'
print "$hashref_copy->{data}\n"; # Outputs 'b'

Answer 3

When you copy a hashref into another scalar, you are copying a reference to the same hash. This is similar to copying one pointer into another, but not changing any of the pointed-to memory.

You can create a shallow copy of a hash easily:

my $copy = { %$source };

The %$source bit in list context will expand to the list of key value pairs. The curly braces (the anonymous hash constructor) then takes that list an creates a new hashref out of it. A shallow copy is fine if your structure is 1-dimensional, or if you do not need to clone any of the contained data structures.

To do a full deep copy, you can use the core module Storable.

use Storable 'dclone';

my $deep_copy = dclone $source;