$ perl -we '
my @arr = 1 .. 10;
my $max = 3;
print join ", ", map { $_ == 0 || $_ % $max ? $arr[$_] : "\n$arr[$_]"   } 0 .. $#arr;
print "\n";
'
1, 2, 3,
4, 5, 6,
7, 8, 9,
10