Replace text inside bracketed shortcodes with PHP

One of our customers required some text decoration in a text field of a third-party Wordpress plugin where no provision was available to write HTML in the contents of that field. We cheated a bit by adding bracketed shortcodes.

Suppose you have a text like this:

## End result (could be)
This is a text where this part is [important]very important[/important].
[sidenote]This remark is a sidenote to this important text[/sidenote].
[obsolete]This is obsolete and maybe removed soon[/obsolete]
[underlined]For your eyes only[/underlined]

Here we have three bracketed shortcodes:

• important
• sidenote
• obsolete
• underlined

But you can have your own shortcodes as long as they are not in conflict with any shortcode plugins you are using wherever you want to use them (like: Wordpress, October CMS or any other).

What we want to achieve

We want the string that is returned or echoed to contain:

<h2>End result (could be)</h2>
This is a text where this part is <strong>very important</strong>. 
<i>This remark is a sidenote to this important text</i>.
<strike>This is obsolete and maybe removed soon</strike>
<u>For your eyes only</u>

PHP preg_replace

With the PHP preg_replace, not favored by everyone, function you can search for a (regular expression) pattern and when found replace it with something else. Just like str_replace, but preg_replace is able to replace content based on the result of a regular expression. Just as we will see in the sample below.

...
$html = textDecoration($html);
echo $html;
....

function textDecoration($html)
{
    /**
     * see: https://www.php.net/manual/en/function.preg-replace.php
     */

    $patterns = [
        '/\[(important)\](.*?)\[\/\1\]?/',
        '/\[(sidenote)\](.*?)\[\/\1\]?/',
        '/\[(obsolete)\](.*?)\[\/\1\]?/'
    ];

    $replacements = [
        '<i>$2</i>',
        '<strong>$2</strong>',
        '<strike>$2</strike>'
    ];

    return preg_replace($patterns, $replacements, $html);
}

Let's have a look at the pattern structure:

'/\[(important)\](.*?)\[\/\1\]?/'

There are 2 groups in this structure

• (important) $1
• (.*?) $2

The indicators $1 and $2 can be used in the $replacements array.

So the replacement structure (HTML) is now:

'<i>$2</i>'

Please notice that you can have the patterns and replacements as an array, where every pattern position corresponds with its replacement position.

The variable is $2 and not $1, for all replacements would be the name of the shortcode itself. The variable relates to the group. As said earlier the structures have 2 groups encapsulated by '()' in the regular expression.

End result (could be)

This is a text where this part is very important.

This remark is a sidenote to this important text.

This is obsolete and maybe removed soon

For your eyes only