use strict;

my $number = 1234567890;
print STDOUT "In: $number\n";

my $reversed = reverse($number);
print STDOUT "Reversed: $reversed\n";

my @array = split/(\d{3})/, $reversed;
shift @array;
print STDOUT "Array: '" . join ("' - '", @array) . "'\n";

my $out = join("", map { $_ eq '' ? ',' : reverse($_) } @array);
print STDOUT "Out: " . reverse($out) . "\n";

exit 0;