WP Cron - how to use and how to extend

add-cron-task.php

<?php
// Set up task when plugin is activated
register_activation_hook(__FILE__, 'dcwd_cron_status_setup_schedule');

// On an early action hook, check if the hook is scheduled - if not, schedule it.
function dcwd_cron_status_setup_schedule() {
  // Add the event only if it is not already scheduled.
	if ( ! wp_next_scheduled( 'dcwd_cron_status_status_email' ) ) {
        // Schedule weekly at 2:12am.
        wp_schedule_event( mktime(2,12,0), 'weekly', 'dcwd_cron_status_status_email');
	}
}

// Clear the scheduled task when the plugin is deactivated.
register_deactivation_hook(__FILE__, 'dcwd_cron_status_status_email_deactivation');
function dcwd_cron_status_status_email_deactivation() {
	wp_clear_scheduled_hook('dcwd_cron_status_status_email');
}


function dcwd_cron_status_status_email() {
  // Send the email.
}

plesk-cron-command.txt

/usr/bin/php -q /usr/local/webspace/httpdocs/damiencarbery.com/wp-cron.php

send-weekly-email.php

<?php
function dcwd_cron_project_send_status_email() {
    // Do a query based on the date.
    // Examples at: https://codex.wordpress.org/Class_Reference/WP_Query#Date_Parameters
    $args = array(
        'date_query' => array(
                          array(
                            'year' => date( 'Y' ),
                            'week' => date( 'W' ), // You may need to -1 to get the posts of the previous week
                          ),
                        ),
    );
    $query = new WP_Query( $args );
    
    $message = '';
    if ( $query->have_posts() ) {
	    $message .= '<ul>';
	    while ( $query->have_posts() ) {
		    $query->the_post();
		    $message .= sprintf( '<li><a href="%s">%s</a></li>', get_the_permalink(), get_the_title() );
	    }
	    $message .= '</ul>';
	    wp_reset_postdata();
    } else {
        $message .= '<p>No posts for this week.</p>';
    }

    $subject = 'Recent Posts';

    // Send the email to the site admin.
    add_filter( 'wp_mail_content_type', 'dcwd_cron_status_set_html_content_type' );
    $headers[] = 'From:  '.get_bloginfo( 'admin_email' );
    wp_mail( get_bloginfo( 'admin_email' ), $subject, $message, $headers );
    // Reset content-type to avoid conflicts -- http://core.trac.wordpress.org/ticket/23578
    remove_filter( 'wp_mail_content_type', 'dcwd_cron_status_set_html_content_type' );
}

function dcwd_cron_status_set_html_content_type() {
  return 'text/html';
}

wp-config-disable-cron.php

<?php
// Disable WP Cron as it will be invoked manually.
define('DISABLE_WP_CRON', 'true');

wp-cron-add-recurrance.php

<?php
/*
Plugin Name: WP Cron: Add Recurrance Options
Plugin URI: http://www.damiencarbery.com
Description: Add 'weekly' and 'biweekly' recurrance values. From <a href="http://www.smashingmagazine.com/2013/10/schedule-events-using-wordpress-cron/">Schedule Events Using WordPress Cron</a>.
Author: Damien Carbery
Version: 0.1
*/

// From: 

add_filter( 'cron_schedules', 'wi_add_weekly_schedule' ); 
function wi_add_weekly_schedule( $schedules ) {
  $schedules['weekly'] = array(
    'interval' => 7 * 24 * 60 * 60, //7 days * 24 hours * 60 minutes * 60 seconds
    'display' => __( 'Once Weekly', 'my-plugin-domain' )
  );
  
  $schedules['biweekly'] = array(
    'interval' => 7 * 24 * 60 * 60 * 2,
    'display' => __( 'Every Other Week', 'my-plugin-domain' )
  );

  return $schedules;
}