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I write posts about math and computer science. Many of those posts need some previous knowledge. I would like to create a box for some articles with links to these basics, simmilar to UbuntuUsers. In my articles I would like to add them like this

{{previousKnowledge|<a href="...">first</a>|<a href="...">second</a>}}

Does a plugin exist for this task?

Can I create a custom template which does basically replace this text by the following?

<div id="previousKnowledge">
    <li><a href="" id="source-1">first</a></li>
    <li><a href="" id="source-2">second</a></li>
share|improve this question
up vote 1 down vote accepted

First of all : Cool idea. I don't know whether there exists a plugin for this task, but I would simply implement this as a new small plugin.

I would recommend changing your syntax, so that it won't contain the links as html.

I changed it to:


Here is my simple first approach :

     Plugin Name: Previous Knowledge
    Plugin URI: TODO
    Description: TODO
    Author: xaeDes
    Version: 0.1
    Author URI: TODO
    License: GPL2

    function previous_knowledge_preg_replace_callback( $matches ) {
        //$matches[1] contains the '...' in '{{previousKnowledge|...}}'
        $items = explode("|", $matches[1]);
        $replaced = '<div id="previousKnowledge"><ul>';
        foreach( $items as $item ) {
            $item_info = explode("=",$item);
            $replaced .= "<li><a href='${item_info[1]}'>${item_info[0]}</a></li>";
        $replaced .= '</ul></div>';
        return $replaced;

     * Looks for occurrences of {{previousKnowledge|...}} tags and replaces them by html.
     * @param string $content
     * @return string
    function previous_knowledge_content_filter( $content ) {
        return preg_replace_callback('#{{previousKnowledge\\s*\\|(.+)}}#i','previous_knowledge_preg_replace_callback', $content);

    add_filter( 'the_content' , 'previous_knowledge_content_filter' );

I tested with your example and it works.

You may change the output html in previous_knowledge_preg_replace_callback(..).

How to install it in your wordpress :

  1. Create a folder named 'previous_knowledge' (or whatever name you find appropriate) in wp-contents/plugins/.

  2. Create a php file named previous_knowledge.php inside this folder and paste the code into the file.

  3. Now you only have to activate it and put "{{previousKnowledge|first=...|second=...}}" into your posts or pages.

Do you want further explanations?

share|improve this answer
Hi xaedes, this looks quite good! I have to test it on an offline version of my blog. If it works, I'll accept your answer. At the moment I just gave you +1. – Martin Thoma Mar 24 '12 at 21:09

Maybe some thing like this:

function previousKnowledge_shortcode( $atts ) {
extract( shortcode_atts( array(
    'urls' => '',
    'titles' => ''
), $atts ) );

$url = explode("|", $urls);
$title = explode("|", $titles);
$c = count($url) - 1;
$code = '<div id="previousKnowledge"><ul>';
for ($i = 0; $i <= $c; $i++) {
    $b = $i +1;
    $code .= '<li><a href="'.$url[$i].'" id="source-'.$b.'">'.$title[$i].'</a></li>';
$code .= '</ul></div>';

return $code;

add_shortcode( 'previousKnowledge', 'previousKnowledge_shortcode' );

the short code will be: [previousKnowledge urls="http://www.site.com|http://www.site2.com|http://www.site3.com" titles="site1|site2|site3"]

and it will preduce the HTML:

<div id="previousKnowledge">
    <li><a href="http://www.site.com" id="source-1">site1</a></li>
    <li><a href="http://www.site2.com" id="source-2">site2</a></li>
    <li><a href="http://www.site3.com" id="source-3">site3</a></li>

NOTICE: I've tested it, so it works :). Let me know if it helps.

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