Wordpress get_option in External PHP file

Question

I have created a plugin that adds products programatically to WooCommerce. The plugin is working great, but now I need to make a cron job that runs every 5 minutes to update the inventory.

I have the script all written but I need to include calls to get_option() in this php file to get certain plugin values that the user has entered. However, I can't just include get_option() in this file because it is outside of the Wordpress core. So my thought would be to put in require( 'path/to/wp-load.php' ); which I know you aren't really supposed to do. Anyway it fixes the issue if you hit the page via a web browser request. However the cron job fails the moment that this file is included because somewhere with wp-load.php it is sending HTTP_Header requests.

Any thoughts or solutions? I tried to add define('WP_USE_THEMES', false); right above the requiring of wp-load.php but it is still causing the cron job to fail.

Long winded I know, but how do you include get_option() requests inside of a external PHP script that will be accessed via a PHP cron job.

Thanks much.

Answer 1

The quick and easy way

The problem is probably that you try to include wp-load.php from a wrong path. In a CLI environment, the path would not be the same as when you do an HTTP request to the file. So with this you should fixed your issue:

require(dirname(__FILE__) . '/../../../wp-config.php');

The proper but longer way

Based on cale_b comments and this article he linked, there is a much proper way to go by doing a Wordpress Cron job.

First in your plugin add a function that will contain the code needed to be executed, let's call it my_cron_job(). You can eventually just include the script you already wrote in this function. Then add the following to schedule the execution of this every 5min:

// Define a new interval (5 minutes)
add_filter('cron_schedules', 'fively_interval');
function fively_interval($interval) {
    $interval['fively'] = array('interval' => 5*60, 'display' => 'Once 5 minutes');
    return $interval;
}

// Register the hook on plugin activation
register_activation_hook(__FILE__, 'my_cron_job_activation');
add_action('my_cron_event', 'my_cron_job');
function my_cron_job_activation() {
    wp_schedule_event(time(), 'fively', 'my_cron_event');
}

// Unregister the hook on plugin deactivation
register_deactivation_hook( __FILE__, 'my_cron_job_deactivation' );
function my_cron_job_deactivation(){
  wp_clear_scheduled_hook( 'my_cron_event' );
}

Then set up your cron to execute wp-cron.php every 5 minutes:

*/5 * * * * php-cli -f [path to your WP]/wp-cron.php

---

Update

First when choosing the option of executing wp-cron.php with a server cron you should disable the default WP Cron behaviour (execution of cron through web visits):

define('DISABLE_WP_CRON', true);

Secondly, as for your question about WP Cron reliability I see a potential flaw indeed. I'm not 100% sure of that, but I think it is possible that wp_schedule_event get desynchronized with the server cron, as the job get executed only if the interval is past. As it will be re-scheduled depending of the execution time of the script which is slightly different with the server cron time.

For example:

00:00:00:000    Server cron execute wp-cron.php
00:00:00:100    The job can be executed, so let it run
00:00:00:200    Wordpress finished to execute the job - it schedule the event in 5min
00:05:00:000    Server cron execute wp-cron.php
00:05:00:100    The job is planned for 00:05:00:200, no execution !
00:10:00:000    Server cron execute wp-cron.php
00:10:00:100    The job is executed

That's theory of course, maybe this is not accurate. I suggest doing some test and see how it behave. If it indeed behave like I think it did, I suggest as easy workaround to change the wp_schedule_event to a lower interval - 4min for example.

add_filter('cron_schedules', 'fourly_interval');
function fourly_interval($interval) {
    $interval['fourly'] = array('interval' => 4*60, 'display' => 'Once 4 minutes');
    return $interval;
}

So we'll have the following:

00:00:00:000    Server cron execute wp-cron.php
00:00:00:100    The job can be executed, so let it run
00:00:00:200    Wordpress finished to execute the job - it schedule the event in 4min
00:05:00:000    Server cron execute wp-cron.php
00:05:00:100    The job is planned for 00:04:00:200, so let it run!
00:10:00:000    Server cron execute wp-cron.php
00:00:00:200    Wordpress finished to execute the job - it schedule the event in 4min
00:10:00:100    The job is executed (planned for 00:09:00:200)

With the default WP Cron behaviour disabled it should work flawlessly.