By default, after publishing codes, the post shows a html like this,

<pre class="wp-block-code">
    <code>
        some codes here
    </code>
</pre>

I have plenty posts with codes and don't want to edit them one by one. How do I add a custom class attribute globally for all posts? to make it look like this

<pre class="wp-block-code custom-class">
    <code>
        some codes here
    </code>
</pre>

Thanks in advance.

By default, after publishing codes, the post shows a html like this,

<pre class="wp-block-code">
    <code>
        some codes here
    </code>
</pre>

I have plenty posts with codes and don't want to edit them one by one. How do I add a custom class attribute globally for all posts? to make it look like this

<pre class="wp-block-code custom-class">
    <code>
        some codes here
    </code>
</pre>

Thanks in advance.

• posts
• functions
• customization
• themes
• filters

• On the right of the editor, there should be an "Advanced" tab. Open that and there'll be an "Additional CSS Class(es)" field. – Jacob Peattie Commented May 7, 2020 at 7:19
• Okay. Any other solution so that it works globally for all posts without editing one by one? – ooneland Commented May 7, 2020 at 7:36
• After deploying the code, I got an error saying, Parse error: syntax error, unexpected ',', expecting variable(T_VARIABLE) – ooneland Commented May 8, 2020 at 7:18
• The code in that answer is JavaScript, not PHP. – Jacob Peattie Commented May 8, 2020 at 7:20
• oops, where should I use that code – ooneland Commented May 8, 2020 at 7:24

1 Answer 1

To add your custom class to the old posts at once, you can do this via "the_content" filter and using preg_replace or preg_replace_callback function to do a REGEX replacement.

A working Example:

add_filter( 'the_content', function( $content ){

    // Don't do anything if we're not in a single post
    if(! is_singular()){
        return $content;
    }

    $customClass = 'custom-class';

    return preg_replace_callback(
        '/<pre([^>]+)class="([^"]+)"/i',
        function( $matches )use( $customClass ){
            return '<pre' . $matches[1] . 'class="' . trim($matches[2]) . ' ' . $customClass . '"';
        },
        $content
    );

} );