# insert these 3 lines if arrays aren't sequential
sub numerical {$a <=> $b}
@array_1 = sort numerical @array_1;
@array_2 = sort numerical @array_2;

my $array_1 = pop @array_1;
my $array_2 = pop @array_2;
while (@array_1) {
    if ($array_1 > $array_2) {
        $array_1 = pop @array_1;
    }
    elsif ($array_2 > $array_1) {
        $array_2 = pop @array_2;
    }
    else {
        print "highest common divisor = $array_2\n";
        last;
    }
}