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I wanted to use Wordpress built in WP Cron to update currency rates daily.

I use this function currently,

require_once(WP_PLUGIN_DIR . '/autocurupdate/currencyexchange_class.php');
$cx=new currencyExchange();
$currency_sql = "select last_updated from " . $wpdb->prefix."currencies where code = 'PHP'";
$currency_1 = mysql_query($currency_sql);
$currency_2 = mysql_fetch_array($currency_1);
$last_updated = mysql2date(get_option('date_format'), $currency_2['last_updated']);
$current_date = $cx->Date;
$currentdate = mysql2date(get_option('date_format'), $current_date);
if($last_updated !== $currentdate) {

How can I run update_currency() function daily using WP Cron?

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Ken, any progress on that question? – kaiser Oct 29 '13 at 22:25

First things first: Say hello! to $wpdb

The wpdb Class is what you take to interact with the database on it's most basic level. Forget all those mysql_* functions, when it comes to WordPress. The core has a nice wrapper, that makes most things pretty safe for you (hint: SQL-injections and other bad boys). Or at least offers things, that you can use to make it safe (like_escape(), $wpdb->prepare() to mention some).

The Schedule API

WordPress comes with some sort of pseudo Cron Job:

  • Schedule API It's not that well documented, but this is what comes a real Cron Job closest. Make sure, that you read everything about it and try it in a clean install.

I have written a small plugin, that will allow you inspect what you're doing. It's called »WP Cron Jobs List« and is hosted on GitHub/Gist or via our own WPSE Plugin repository.

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This is how works the cron

add_action('my_daily_event', 'update_currency');
add_action('wp', 'my_activation');

function my_activation() {
if ( !wp_next_scheduled( 'my_daily_event' ) ) {
    wp_schedule_event( time(), 'daily', 'my_daily_event');

This should work. But wordpress cron works when someone visits your site and the scheduled time has been passed.

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