$ perl -le '$n = () = split /,/, "1,2,3,4,5"; print $n'
1
$ perl -le '$n = ($a) = split /,/, "1,2,3,4,5"; print $n'
2
$ perl -le '$n = ($a, $b) = split /,/, "1,2,3,4,5"; print $n'
3
$ perl -le '$n = ($a, $b, $c) = split /,/, "1,2,3,4,5"; print $n'
4