my $string = '1,3,5,7,9,1,3,4,5,6,2,1,5,6,7,9';

our %counts;
my $x = "$string,";
1 while $x =~ /([^,]*),(?{ $counts{$1}++ })/g;

for my $num (sort { $a <=> $b } keys %counts) {
   print "$num\t$counts{$num}\n";
}