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[obsolete]This is obsolete and maybe removed soon[/obsolete]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This is obsolete and maybe removed soon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

Links

You can create your own replacement regular expressions online with this great regex tester and builder: Regex101

1. Select "substitution" to create a preg_match regular expression
2. Place here your regular expression that should filter the test string (5) = pattern
3. Place here the string that should replace the pattern entered
4. Here it will present the outcome based on the calculated pattern
5. Enter here an example like how it could exist in your own string to match