Here's how to do just the 'round robin' part.

my @dirs = qw{ dir1 dir2 dir3 };
my $num_targets = $#dirs + 1;

my $counter = 0;
foreach (0..10) {
        my $target = $dirs[$counter % $num_targets];

        print "$_ => $target\n";

        $counter++;
}
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The % operator gives you the remainder of the division of $counter / $num_targets, which will be 0, 1 or 2 for any value of $counter. Use that number to select the proper directory out of the array.

Run this little snippet and you can see the result...

/\/\averick
OmG! They killed tilly! You *bleep*!!