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

my $ref1=
    {
   
        ref1_specific_key => 'some value',
        
        common_key =>
        {
            common_subkey => 'foo'
        }
        
    };
    
my $ref2=
    {
    
        ref2_specific_key => 'some other value',
    
        common_key =>
        {
            common_subkey => 'bar'
        }
        
    };

my $output = { %$ref1, %$ref2 };

print Dumper $output;