Before writing a one-liner, try writing the code as a .pl file with

use strict;
use warnings;
[download]

Your code actually does give an output:

C:\....\Projects>perl -wE "@a=1..9; $i=0; say @a[$i..($i+=3)-1] while 
+$i<@a"




C:\....\Projects>perl>
[download]

Those blank lines are "output".