Another approach to this is to recognize that your sequence of strings can form a one-to-one map with a sequence of integers.

The advantage of this method is that it uses no memory.

# XXX Doesn't handle negatives
sub idiv {
    my ($dividend, $divisor) = @_;
    use integer;
    my $quotient  = $dividend / $divisor;
    my $remainder = $dividend - ( $quotient * $divisor );
    return ( $quotient, $remainder );
}

my @chartab = (0..9, 'a'..'z');
my $N = 3;
for (0 .. @chartab**$N-1) {
    my $x = $_;
    for (1..$N) {
        ($x, my $i) = idiv($x, 0+@chartab);
        print $chartab[$i];
    }
    print ',';
}
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