谁能帮忙看看这个脚本错在哪里

地球发动机

需求：递归读取目录下所有文件，并给出一个列表

程序：
#######程序开始#######
#! /usr/bin/perl

sub ReadDir
{
  my ($path)=@_;
  opendir(DIR,$path);
  my @files=readdir DIR;
  closedir(DIR);
  return @files;
}

sub ShowDir
{
  my ($path)=@_;
  my @files=ReadDir($path);
  for(@files)
  {
    if($_=~m/^.{1,2}$/)
    {next;}
    print $path."/".$_."\n";
    if(-d $_)
    {
      ShowDir($path."/".$_);
    }
  }
}

ShowDir(".");
########程序结束#######
现在的问题是，为什么这个程序仅深入到2层，就无法再进入了？
例如，把以上文件保存为showdir.pl，在Linux源代码目录下执行
./showdir.pl | grep 'Makefile' -r
结果是：
./Makefile
./block/Makefile
./crypto/Makefile
./drivers/Makefile
./drivers/block/Makefile
./drivers/crypto/Makefile
./drivers/net/Makefile
./init/Makefile
./ipc/Makefile
./kernel/Makefile
./lib/Makefile
./net/Makefile
./scripts/Makefile
./scripts/Makefile.build
./scripts/Makefile.clean
./scripts/Makefile.headersinst
./scripts/Makefile.host
./scripts/Makefile.lib
./scripts/Makefile.modinst
./scripts/Makefile.modpost
./security/Makefile
./sound/Makefile
./sound/drivers/Makefile
./usr/Makefile
./Makefile.lst
与（正确的）find . -iname 'Makefile'的输出相比，少了很多。

dajun

readdir DIRHANDLE
               Returns the next directory entry for a directory opened by
               "opendir".  If used in list context, returns all the rest of
               the entries in the directory.  If there are no more entries,
               returns an undefined value in scalar context or a null list in
               list context.

               If you're planning to filetest the return values out of a
               "readdir", you'd better prepend the directory in question.
               Otherwise, because we didn't "chdir" there, it would have been
               testing the wrong file.

                   opendir(DIR, $some_dir) || die "can't opendir $some_dir: $!";
                   @dots = grep { /^\./ && -f "$some_dir/$_" } readdir(DIR);
                   closedir DIR;