You are also trying to rename the directories and anything else listed (and matched) in that directory. (such as '..'). This is probably not what you want to do:

Try this to read in only the files.

@files = grep {  -f "$dir/$_" } readdir(DH);
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UPDATE: Or in chapter 9.5 of the Cookbook:

use DirHandle;

sub plainfiles {
   my $dir = shift;
   my $dh = DirHandle->new($dir)   or die "can't opendir $dir: $!";
   return sort                     # sort pathnames
          grep {    -f     }       # choose only "plain" files
          map  { "$dir/$_" }       # create full paths
          grep {  !/^\./   }       # filter out dot files
          $dh->read();             # read all entries
}
[download]

also please do not link to 'illegal' copies of books here...