What is the best approach to detect changes in a variable in a .php file on a server for a client to process?

One approach to detect changes in a variable in a .php file on a server for a client to process is to use file modification time. By checking the last modification time of the file, you can determine if the variable has been updated since the last check. This can be done by comparing the current modification time with a previously stored timestamp.

<?php
$filename = 'yourfile.php';
$storedTimestamp = filemtime($filename);

// Check if the file has been modified
if($storedTimestamp != filemtime($filename)){
    // Variable has been updated, process the changes
    // You can fetch the variable value from the file and do further processing here

    // Update the stored timestamp
    $storedTimestamp = filemtime($filename);
}
?>