Or generalize as a general-purpose routine so you don't have to write another one next time:

sub make_rand_str {
   # e.g.: $str = make_rand_str(8, 'A'..'Z','2'..'9');
   my ($num_chars, @possible_chr_array) = @_;
   my $num_possibles = @possible_chr_array;
   my $rnd_str = "";
   for (1..$num_chars) {
      $rnd_str .= $possible_chr_array[rand($num_possibles)];
   }
   return $rnd_str;
}
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