sub break_by {
    my ($by, $data) = @_;
    my $i = 0;
    return sub {
        my $n = @$data - $i;
        $n = $n < 0 ? 0 : $n > $by ? $by : $n;
        $i += $n;
        return @$data[$i-$n..$i-1];
    }
}    

my @data = ( 1,2,3,4,5,6,7,8,9,10,11,12 );

my $iter = break_by(5, \@data);
while (my @group = $iter->()) {
   print("@group\n");
}