PHP: killing a process by its process-Id/PID, platform-independent and library-independent

The are many scenarios where it is necessary to keep track of spawned process PID's and kill them either gently (e.g. a SIGTERM via taskkill /PID on Windows or kill -15 on Linux,MacOS) or not so gently (e.g. SIGKILL via taskkill /F /PID on Windows or kill -9 on Linux,MacOS).

In PHP there is an easy way to get the current processID of the running script. The function is aptly named getmypid(). To facilitate easy termination of a process, such as a process spawned by a PHP script via popen or exec, I wrote a concise one-liner: