sub recurse_me {
  my $dir = shift;
  opendir FOO, "$dir" or die "Couldn't open $dir: $!;
  while( readdir FOO ) {
    if ( -d $_ ) {
      push @dirs, $_;
    }
    else {
      # do something interesting
    }
  }
  closedir FOO;

  recurse_me( $_ ) for ( sort @dirs );
}