Your problem is that you are trying to open the current directory "."
and the parent directory ".." which are returned in @files when you
perform the readdir(). The following code will solve your problem

#!/usr/bin/perl
$dir = "/temp";
opendir (DIR,$dir) or die "Can't open folder $dir: $!\n";
      @files = readdir DIR or die "Couldn't read from $dir: $!\n";

      foreach $file (@files)
      {
        if (($file ne ".") and ($file ne ".."))
        {
                $/=undef;
                open MYFILE, "$file" or die "Cannot open :$!\n";
                print MYFILE "$file \n";
                close FILE;
                $/="\n";

        }
      }
      closedir DIR;
[download]

Hope this is of help.