sub chunks{ 
    my( $n, @in ) = @_; 
    join ",\n", map join(' ', splice @in, 0, $n), 0 .. $#in / $n;
};;

print chunks( 3, 'a'..'z' );;
a b c,
d e f,
g h i,
j k l,
m n o,
p q r,
s t u,
v w x,
y z

print chunks( 10, 'a'..'z' );;
a b c d e f g h i j,
k l m n o p q r s t,
u v w x y z

print chunks( 26, 'a'..'z' );;
a b c d e f g h i j k l m n o p q r s t u v w x y z

print chunks( 13, 'a'..'z' );;
a b c d e f g h i j k l m,
n o p q r s t u v w x y z

print chunks( 6, 'a'..'z' );;
a b c d e f,
g h i j k l,
m n o p q r,
s t u v w x,
y z