为什么没有错误存储在指定的error_log文件中？

I want to save errors from a specific file in a custom file, Not the default file.

So I added that at the top of my script:

ini_set("log_errors", TRUE);
ini_set("error_log", get_template_directory_uri() . "/errors.log");

Then I removed a character from a function to create an error:

echo $date->fomat("F j, Y");
//Should be format("F j, Y")

That caused a fatal error:

Fatal error: Call to undefined method DateTime::fomat()

But I can't see any text in the log file.

I read a comment saying that ini_set works only when the code is executed, So I have to edit that function in php.ini.

But I want only to save that script errors in that custom file, Not all the errors, As I will parse that errors into a section on the website.

I can't use :

try {
    //Script Here.
} catch (Exception $e) {
    file_put_contents(get_template_directory_uri() . "/errors.log", $e->message);
}

Because that won't get all the fatal errors, Warnings and notices.

What to do then to get that script errors saved in a separate file?