Please use <c>...</c> around your code.

On which OS will your run your code?

• On the Mac, \r is LF and \n is CR, so don't use \r and \n.
• On the Mac, the line is ended by CR, so checking for CRLF on a line basis won't work
• On Windows, you need to use binmode. CRLF becomes LF when a file is read without binmode.
• On unix, what you have should work.

Fix:

# Works on unix.
# Works on Windows.
# Still doesn't work on Mac.

open(IN, '<', $input_file)
   or die "Couldn't open file $input_file: $!\n";
binmode(IN);
while (<IN>) {
   if (/\x0D\x0A/) { die("DOS files not allowed\n"); }
   $total_lines++;
}
[download]

Update: Here's something that works everywhere:

# Works on unix.
# Works on Windows.
# Works on Mac.

{
   open(my $fh, '<', $input_file)
      or die "Couldn't open file $input_file: $!\n";
   binmode($fh);
   my $buf = '';
   while (read($fh, $buf, 1024, length($buf))) {
      if (/\x0D\x0A/) { die("DOS files not allowed\n"); }
      $buf = substr($buf, -1);
   }
}


{      
   open(my $fh, '<', $input_file)
      or die "Couldn't open file $input_file: $!\n";

   while (<$fh>) {
      $total_lines++;
   }
}
[download]