walktree('d:/perl');

sub walktree {
  print "$_[0]\n"; # or real-world stuff here
  for ( glob("$_[0]/*") ) {
    -d && walktree($_);
  }
}

##</code><code>##

  for (grep(-d, glob("$_[0]/*"))) {
    walktree($_);
  }

  walktree($_) for (grep(-d, glob("$_[0]/*")));