[0] Perl> sub do3{ print "@_" };;
[0] Perl> @a = 1 .. 20;;
[0] Perl> do3 @a[ $_ .. $_ +2 ] for map{ $_ * 3 } 0 .. $#a / 3;;
1 2 3
4 5 6
7 8 9
10 11 12
13 14 15
16 17 18
Use of uninitialized value in join or string at (eval 3) line 1, <STDIN> line 3.
19 20