As used, { } creates an (anonymous) hash, assigns the contents of the curlies to that hash, and returns a reference to that hash.

In the first snippet, you create a new hash in every pass of the loop. You assign a reference to the newly created hash to $r->{cat}. Thus, every record references a different hash.

In the second snippet, you create one anonymous hash outside the loop. You assign a reference to that hash to $r->{cat}. Thus, you have multiple records referencing that one hash.

I am sorta following you... here is a much more testable example:

use strict;
use warnings;
use Data::Dumper;

my $data1 = [
        { "shape" => "round", "food" => "apple" },
        { "shape" => "square", "food" => "pear" }
];

my $data2 = [
        { "big" => "cow", "small" => "bunny" },
];

my $combined;

foreach my $r (@{$data1}) {
        $r->{sizes} = $data2;
        push(@{$combined},$r); 
}

print Dumper($combined);
[download]

Which of course produces the same result just as you explain. But after messing with this I am not able to make it do what I want.

I suppose it is because I am not really grasping it totally, which bothers me because I thought I had references down.

Can you modify the code above to produce the result I am looking for... do you see what I am trying to do? $data2 needs to reside outside that loop and I am wanting this result:

$VAR1 = [
          {
            'food' => 'apple',
            'shape' => 'round',
            'sizes' => [
                         {
                           'small' => 'bunny',
                           'big' => 'cow'
                         }
                       ]
          },
          {
            'food' => 'pear',
            'shape' => 'square',
            'sizes' => [
                         {
                           'small' => 'bunny',
                           'big' => 'cow'
                         }
                       ]
          }
        ];
[download]

Thanks! Thanks!

Can you modify the code above to produce the result I am looking for...?

You are making a shallow copy. You need a deep copy.
Change this:

        $r->{sizes} = $data2;
[download]

to:

        $r->{sizes} = [ map { { %{$_} } } @{$data2} ];
[download]

or

use Clone qw( clone );
        $r->{sizes} = clone($data2);
[download]

or

use Clone::PP qw( clone );
        $r->{sizes} = clone($data2);
[download]

or

use Storable qw( dclone );
        $r->{sizes} = dclone($data2);
[download]