Calculate the check digit in a Portuguese NIF

nif.pl

use strict;
use warnings;

sub nif_check {
    my ($nif) = @_;
    my $check = 0;
    foreach my $i (reverse 0..7) {
        $check += substr($nif, $i, 1) * (9-$i);
    }
    $check %= 11;
    if ($check < 2) {
        $check = 0;
    } else {
        $check = 11 - $check;
    }

    print "$nif $check\n";
}

nif_check($ARGV[0]);