Adding a cron job to a WordPress plug-in

plug-in-cron.php

// When the plugin is activated, schedule a weekly event for a specific task
function custom_plugin_activate() {
    // Check if the event isn't already scheduled
    if (!wp_next_scheduled('custom_task_hook')) {
        // Schedule a weekly event using WordPress cron
        wp_schedule_event(time(), 'weekly', 'custom_task_hook');
    }
    // Call the function to perform the task immediately upon activation
    perform_custom_task();
}
// Hook the function to plugin activation
register_activation_hook(__FILE__, 'custom_plugin_activate');

// Function to be executed by the cron job
function perform_custom_task() {
    // Include the required file for performing the task
    require_once(plugin_dir_path(__FILE__) . 'cron/custom_task_file.php');
    // Call the function that handles the task
    execute_custom_task();
}

// Hook the custom task function to the custom action
add_action('custom_task_hook', 'perform_custom_task');

// When the plugin is deactivated, remove the scheduled event
function custom_plugin_deactivate() {
    // Get the timestamp of the next scheduled event
    $timestamp = wp_next_scheduled('custom_task_hook');
    // Unschedules the event
    wp_unschedule_event($timestamp, 'custom_task_hook');
}
// Hook the function to plugin deactivation
register_deactivation_hook(__FILE__, 'custom_plugin_deactivate');