You are almost there. You can use the % operator (modulus) to find each fifth number. If modulus 5 returns 4, output a newline, otherwise, output a space:

#! /usr/bin/perl
use strict;
use warnings;

use List::Util qw{ shuffle };

my @numbers = shuffle(1 .. 50);
for my $index (0 .. $#numbers) {                          # replace wi
+th 0 .. 25 to stop after 5 lines.
    print $numbers[$index], $index % 5 == 4 ? "\n" : ' ';
}
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