Here's a method using Algorithm::Combinatorics.

use Algorithm::Combinatorics qw(variations_with_repetition);

my $length = 4;
my @data = qw(1 2 3);
my $iter = variations_with_repetition(\@data, $length);
while (my $p = $iter->next) {
    print join("",@$p)."\n";
}
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