Sister dir path in PHP

In PHP, we can get the path of the directory which is one level up in the hierarchy using the dirname() function.

Here is an example:

Suppose we have the following directory structure:

- project
  - app
    - index.php
  - config
  - public

If we are working in index.php file which is located in the app directory and we want to get the path of the config directory which is located in the parent directory of app, we can use the dirname() function as follows:

$config_dir = dirname(__DIR__) . '/config';
echo $config_dir; // output: /path/to/project/config

The __DIR__ magic constant returns the absolute path of the current directory (app). We then use the dirname() function to get the path of the parent directory (project). Finally, we concatenate the path of the config directory to the parent directory path to get the complete path of the directory.

Note that we use forward slash (/) as directory separator instead of backslash (\) because PHP works with forward slash as the directory separator regardless of the operating system used.