I need to use exec() in my PHP script to call another (long-running) PHP script.

I am currently trying to create a couple of simple test scripts, but I end up with an infinite loop.

test.php is my initial script and simple.php is the script that it calls via exec().

simple.php:

<?php
error_log('simple.php called.');
echo 'OK';

simple.php works fine if I go into Terminal and execute:

php tasks/simple.php

But when I try and call it via exec() in test.php, I end up with an infinite loop. The code shows the commands I've tried, along with the result for each one.

test.php:

<?php

error_log('test.php called'); // Test code to check infinite loop

$cmd = 'dir'; // This works!

//$cmd = 'php tasks/simple.php'; // Loops forever

//$cmd = 'php tasks/simple.php >/dev/null &'; // With this, the browser doesn't get stuck in an infinite loop, but simple.php is called thousands of times

//$cmd = 'php tasks/this-script-does-not-exist.php';// Loops forever

//$cmd = "php /home/public_html/my_test/tasks/simple.php"; // Loops forever

//$cmd = 'php /home/public_html/my_test/tasks/simple.php'; // Loops forever

//$cmd = 'php-cli tasks/simple.php'; // $return_val: 127. $output:
/*
Array
(
)
*/

//$cmd = "php-cli /home/public_html/my_test/tasks/simple.php"; // $return_val: 0. $output:
/*
Array
(
    [0] => X-Powered-By: PHP/8.1.31
    [1] => Content-Encoding: gzip
    [2] => Vary: Accept-Encoding
    [3] => Content-type: text/html; charset=UTF-8
    [4] => 
    [5] => �UWuP\ק㡻a����n�c�٥�xĥ��nYB��nD@��W�]`��}��o��ǝ3w~'��~@E 80���%���'��]��`�@�,@9 �)���=6"vE����o00�*�*0�2z,-�DX����_����R�q�u��q���y��!D�",��˭����?�@�����e``��;��K������4���8��r��i��DX��e��ui�rB
    [6] => ���4!鷁3��J�Y���?�5��L�](.R�]E��VBO�_�}^���\�{f�ȼ��Ez�N:��7����fU�w�6
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    [7] => �prS���&�����ID�E-ײf�\j-��"�`0���YFP��������֠D�����eAk+{ж��R7ʹj׉��w{�-l4>�L�Z�%�͌�w殿��B�`�A%6\