PHP has built-in web server that designed to use for testing, development or application demonstration purposes. Since 8.0, built-in web server allows to bind to port 0. It will use a system-generated port that is currently available.
We can execute the following command to start built-in web server:
php -S localhost:0
We specified port 0. So operating system selects a random unused port. Then built-in web server will bind to that port and starts listen for incoming requests.
[Sun Dec 6 15:05:25 2020] PHP 8.0.0 Development Server (http://localhost:63809) started