#!/usr/bin/perl
use warnings;
use strict;

use Data::Dumper;

my $str1 = 'a,b,c';
my $str2 = '1,2,3';

my ($strA, $strB) = ($str1, $str2);
$strA =~ s/,/',' . do { $strB =~ s=([^,]+),==; $1 } . ','/eg;

my %hash2 = split /,/ => "$strA,$strB";
print Dumper \%hash2;