Replace custom gallery shortcode with default gallery shortcode

Question

I want to replace my custom gallery shortcode in my post content with the default Wordpress shortcode (in pre get posts). I will be doing this in only a certain instance where it will need to be formatted in the default gallery shortcode format (in order to work with exporting to Apple News).

How can I search through the content for my custom gallery shortcode:

[showgallery id="1234"]

And then replace it with the default one:

[gallery ids="1234,1235,1236,1237,1238"]

I can handle the changing it from one id to the several ids by just creating a custom function that will just grab the one id, fetch that post, grab the array of images within that post (I use ACF galleries), and then return the list of ids.

So I just need to know how to search through the content, find each showGallery shortcode, and then for each of those shortcodes grab the id, send it to my custom function, remove the old shortcode, and then replace it with the new one that would be returned by my function.

I found this which seems close, but still can't figure out fully how to remove the old one, etc.

Extract attribute values from every shortcode in post

Answer 1

Either make a regex filter as a the_content filter,

add_filter('the_content', 'my_regex_filter', 1); // Execute as early as possible

function my_regex_filter($content) {
    $regex = get_shortcode_regex(array('showgallery'));
    $content = preg_replace('/'.$regex.'/s', '[$1gallery$3$4$5$6]', $content );
    return $content;
}

or rewrite your add_shortcode function.

remove_shortcode('showgallery');
add_shortcode('showgallery', 'my_showgallery');

function my_showgallery($args) {
    return gallery_shortcode($args);
}

I would recommend the second, because it is cleaner and faster.

Edit:

Rewriting the shortcode for external plugins.

In your functions.php define the plugin version of your shortcode:

remove_shortcode('showgallery');
add_shortcode('showgallery', 'my_showgallery');

function my_showgallery($args) {
    return gallery_shortcode($args);
}

function my_template_gallery($args) {
    // Here put your custom gallery code…
}

Add to your header.php the following two lines:

remove_shortcode('showgallery');
add_shortcode('showgallery', 'my_template_gallery');

Now you got the rendered WP shortcode everywhere except on your templates.