use strict;
use warnings;
use Data::Dumper;
 
my @key = qw(x y z);
my %hash;
 
while (<DATA>) {
   chomp;
   @hash{@key} = split ',';
   print Dumper \%hash;
}
 
__DATA__
a,b,c
a,b
a,b,c,d
a,,,