Perhaps you don't want a hash at all. Or perhaps you want to do something with the elements in their original order before you build a hash. In either case, start by extracting all the pairs, then splitting them into their components. Then do whatever you're going to do with them (including, perhaps, inserting them in a hash).

use strict;
use warnings;

my $str='1,zxc,2,asd,3,qwe';
foreach ( $str =~ /([^,]+,[^,]+)/g ) {
  my ($k, $v) = split /,/;
  print "Do something with key $k and value $v\n";
}
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Update:
I had a "duh" moment. You can, of course, extract the elements like so:

foreach (my ($k,$v) = $str =~ /([^,]+),([^,]+)/g) {
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