The issue is to split into fields but keep those grouped by parantheses together. For comma-separated data it is always advisable to use a module like Text::CSV rather that splitting yourself. Text::CSV cannot directly treat parantheses but if you replace them with double quotes it should work fine.

UPDATE: here is some sample code:

use strict;
use warnings;
use Text::CSV;

my %pets;
my @info;

$info[0]="Mary,Owens,cat,white";
$info[1]="Bill,Thompson,(cat,dog),(white,black)";
$info[2]="Bill,Thompson,(hamster,cat),(black,brown)";
$info[3]="Bill,Smith,(goldfish,dog,turtle),(yellow,spotted,green)";

s/[()]/"/g for @info;

my $csv = Text::CSV->new();
for (@info) {
    $csv->parse( $_ );
    print join ":", map { "\"$_\"" } $csv->fields();
    print "\n";
}
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