You are accessing the hashref as an arrayref, and then pushing data onto an array that now holds a ref to a hash %$data_b as the first item. You need to access the hashref in a slightly different way to a single element list arrayref.

Elements are acccessed from the inside out rather than the outside in. To 'push' on to hashes you may like to do something like this. Using the keyword each

use diagnostics -verbose;

 while( my ( $key, $value ) = each %$data_a ){
      
    $data_b->{ $key } = $value
    
    }

 printf "%10s%12s\n", 'key:', ':value';

        
 while( my ( $k, $v ) = each %$data_b ){
    my $c;      
    printf "%9s%-8s%-11s\n", $k, ++$c % 2 == 1 ?  '  ---  ' : '', $v; 
    
    }


__END__   
      key:      :value
    house  ---   main
    first        Mary
   number  ---   0123
     area        north
 fullname  ---   Ms Mary Lou
     last        Lou
     code  ---   zip
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Also regarding Not A Hash error, try commenting out the push @{ $data_b }, ... line first. By accessing it as an array, you have wrapped it in an anonymous array. Which it now thinks it is.

# <- comment
#  push @{ $data_b }, $actually_im_not_parsed
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