读取我的文件时出现意外输出

Question

Everytime I use echo readfile('./'); die; It just outputs 0, when I want it to read the files in the directory. I also tried

$files_open = readfile('./');
$original_file = explode("
", $files_open);
print_r ($original_file);
die;

I get the same answer:

"0"

Is there another code or anything I could use to read my file? With my directory path being './' ?