PHP uses

see also the command "man php" in Unix-like shell (MSYS, Debian, etc)

php -a

this is the PHP REPL. one statement at a time, usually. useful to test-run some code. also good for teaching/demonstrating.

php script-file.php

this executes a script file. this is a batch execution of the many statements in the script file.

php -S localhost:80

this responds to HTTP requests, executing HTTP-requested script files, staying active as a process in run-loop.