Share: Do not use relative paths when requiring or including in PHP

require_once('../../lib/some_class.php');

Disadvantages of this way of writing: It first looks for the specified php include path and then the current directory. So too many paths are checked. If the script is included by a script in another directory, its base directory becomes the directory where the other script is located.

Another problem is: when the scheduled task runs the script, its parent directory may not be the working directory.

So the best option is to use an absolute path, for example:

define('ROOT' , '/var/www/project/');
require_once(ROOT . '../../lib/some_class.php');

The above code defines an absolute path, and the value is hard-coded.

Next, with improvements, the path /var/www/project may also change, so do you need to change it every time? No, you can use the __FILE__ constant, for example:

define('ROOT' , pathinfo(__FILE__, PATHINFO_DIRNAME));
require_once(ROOT . '../../lib/some_class.php');

Now , no matter which directory it is moved to, such as moving it to an external server, the code will run correctly without any changes. That is to say, pathinfo and __FILE__ constants are used to achieve portable code.