15 useful WordPress Functions you probably don’t know

While I was building my first premium WordPress Plugin – the Avia Feedback Box – I needed to solve quite a few problems I have never encounterd when creating themes. During my research I stumbled upon several really cool wordpress functions that I want to share with you.

WordPress Transient API

set_transient(), get_transient(), delete_transient()

This is a function set very similar to get_options() and update_options() which helps to easily store and retrieve data in your options database table. The big difference here is that you also pass a time parameter which acts as expiration date for the database entry.

Once the time has expired the data is removed. This is especially useful if you want to cache data or query results for a short amount of time. An example would be a twitter widget which retrieves data from the twitter api, but since twitter is down pretty often it would be wise to save that data for a few minutes. That also would speed up the site for subsqequent page requests since you don’t need to connect to an external API.

It works pretty easy: the function set_transient accepts 3 parameters:

set_transient($transient, $value, $expiration);

so saving a value to your database for an hour would look like this:

set_transient('the_name', $special_query_results, 60*60);

getting the value like this:

$value = get_transient('the_name');


WordPress “Cron Jobs”

wp_schedule_event(time(), 'hourly', 'my_schedule_hook');

Schedules a hook which will be executed by the WordPress actions core on a specific interval, specified by you. The action will trigger when someone visits your WordPress site, if the scheduled time has passed.

So if you want to execute some code on a regular base, like checking an RSS Feed, doing a database backup or reseting database values this function will do it for you. Unfortunatley its not as easy to use as transient but here is a short article on how it is done:

WordPress HTTP API

wp_remote_get( $url, $args = array() );

An easy to use function if you want to retrieve the content of a Webpage. The function stores the result within an easily accessible array. Not only do you get the result content of the webpage, you also get header informations and response codes. This function is also capable of retrieving feed content which also makes it useful if you want to create a twitter plugin or an rss reader with wordpress.


Easily Fetch an RSS Feed with WordPress

$feed = fetch_feed( $uri );

fetch_feed is another simple wordpress method to get feed content. It also has the added benefit that it uses the SimplePie and FeedCache functionality for retrieval and parsing and automatic caching.


WordPress mail function

wp_mail( $to, $subject, $message, $headers, $attachments );

$to = 'kriesi@gmail.com';
$subject = 'Hello Kriesi!';
$message = 'This message was sent by wordpress'

$mail = wp_mail($to, $subject, $message);

if($mail) echo 'Mail delivered';

An incredible useful and exceptional easy to use function that also allows you to send headers and attachments, allows plain text sending and html messages and quite a few other options!


WordPress Human Time

human_time_diff( $from, $to )

A feature to mimic twitter like time display. Instead of outputting the time in a basic format you can display it like this:

Kriesi posted 13 hours ago


WordPress get comments


Sometimes its neccessary to retrieve the comments outside of the comments loop like I did with the Avia Feedback Box Plugin, where comments are displayed via ajax. This function helps you in doing so ;)


WordPress validation of strings

wp_kses($string, $allowed_html, $allowed_protocols);

wp_kses is a very usefull function when it comes to sanitizing untrusted user input. This function makes sure that only the allowed HTML element names, attribute names and attribute values plus only sane HTML entities will occur in $string.


WordPress text transformation


A text transformation function that converts commonly used strings into the typographical correct signs. Used for dashes, ellipsis etc and will also add typograpic quotes to certain phrases.



The last text transformation tool on the list is used by wordpress to ad <p> tags to a string by replacing double <br/> tags


WordPress Shortcode API

add_shortcode(), do_shortcode()

add_shortcode() is an easy way to create macros for your post content. for example lets say you want to wrap some content inside the post area within a div with some additional classes and ids that allows you to create multiple columns. you could of course just switch to the html editor and enter

<div class='one_third'>Content goes here</div>

Easier and more convenient especially if you are dealing with customers who dont know html would be a shortcode solution within your functions.php file:

function column_shortcode( $atts, $content = null ) {
   return '<div class='one_third>' . $content . '</div>';

add_shortcode('one_third_column', 'column_shortcode');

You could then use this shortcode in your post content:

[one_third_column]Content goes here[/one_third_column]

If you would like to nest shortcodes within each other you would need to make sure to add the do_shortcode method to your function like this:

column_shortcode( $atts, $content = null ) {
   return '<div class='one_third>' . do_shortcode($content) . '</div>';


Create WordPress post with a php function:


This function inserts posts pages and custom post types in the database. It sanitizes variables, does some checks, fills in missing variables like date/time, etc. very handy when you need to create and insert posts by user input. This function fits perfectly if you have a front end form for example and users can suggest posts.


Create WordPress comment with a php function:


Similar to wp_insert_posts this function inserts a comment. Might also come in handy ;)


WordPress Object Cache:

wp_cache_add(),  wp_cache_set(),  wp_cache_get(),  wp_cache_delete, wp_cache_replace(), wp_cache_flush

WP_Object_Cache is WordPress’ class for caching data which may be computationally expensive to regenerate, such as the result of complex database queries. If you care for theme and plugin performance you should definitley read the wordpress codex entry for this topic!


Kill wordpress execution:


An appropriate end for this post: the wp_die function

wp_die kills the WordPress execution and display HTML message with error message.

A call to this function complements the die() PHP function. The difference is that HTML will be displayed to the user. It is recommended to use this function only when the execution should not continue any further.


48 replies
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  1. Sebastian
    Sebastian says:

    WordPress Shortcode API
    Instead of

    return ‘ ‘ . $content . ‘ ‘;
    I think it should be:-
    return ‘ ‘ . $content . ‘ ‘;
    close spaces where necessary.

    Thank you for the article.

  2. Sebastian
    Sebastian says:

    WordPress Shortcode API
    WordPress Shortcode API
    Instead of
    ‘ <div class = ‘ one_third > ‘

    should be

    ‘ <div class = ” one_third ” > ‘

    close spaces where necessary.

    Thank you for the article.

  3. Mike
    Mike says:

    Very nice article. This will definitely be useful when doing some theme customization. I always wondered how I could make some new shortcodes.

    Thx again.

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  6. sam
    sam says:

    hello,i saw my friend use your avisio wp theme,and i modify some code,because he tell my just need 4 size images,and i delete the code witch in the function.php,eg:$k_option[‘custom’][‘imgSize’][‘S’] = array(‘width’=>70, ‘height’=>50);
    so ,there are just 4 define thumbnail size there,and i found if i upload a pic ,the timthumb plugin would generate a lot of pictures of different sizes,like 290X290 and 300X199 ,this is about the media library images size setting.i didn’t know how to solution this ,bucause i think the upload folder will growing by this,and just like the size about 290X290 I do not need to use them,and i must have to manually delete them.how to solution this problem,thank you very much,and Merry Christmas.my english is so poor ,Laughed. :)

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