my@a=qw(a b c d e f);

my $grpsiz = 2;

if (@a% $grpsiz) {
  push @a, ("") x ($grpsiz - @a % $grpsiz)
}

for (my$i = 0; $i <= $#a; $i += $grpsiz) {

  print @a[$i .. $i+$grpsiz-1]
}