my @a = (1,2,3,4,5,6,7,8,9,10,11,12);
my $n = 4; #parameter
my @lol;
while (@a){
    @lol = (@lol, [splice @a, 0, $n]);
    $i=$i+$n;
    };
print "$lol[2][2]\n"; #for example