In order to to allow "", 0, undef, etc in the array, the general form would be

while (@array) {
   my $item = shift @array;  # or pop
   ...
      push(@array, ...);     # or unshift
   ...
}
[download]

(It's not a problem in your case since every item in @dirs starts with ..)

This model is useful to perform recursive processes without using recursion.