__DIR__ can be used to get the current code working directory. It was introduced starting with PHP version 5.3. It is similar to using dirname(__FILE__). Typically used to include other files that exist within an included file.
Consider the following directory structure -
A directory named "master" with two files named 'worker_1' and 'worker_2'. The master directory itself is a subfolder of the main project directory.
The project directory also contains an index.php file.
Consider there are two files in a directory called inc, which is a subfolder of our project directory, where the index.php file is located -
project_directory ├── master │ ├── worker_1.php │ └── worker_2.php └── index.php
If we execute the code -
include "master/worker_1.php";
From index.php, it runs successfully.
But to run worker_1.php by including worker_2.php, a relative inclusion of the index.php file must be done as shown below -
include "master/worker_2.php";
Using __DIR__ will make it run. The following code can be executed from worker_1.php -
<?php include __DIR__ . "/worker_2.php";
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