OK, so let’s start with Codex:
is an action triggered whenever a post or page is created or updated,
which could be from an import, post/page edit form, xmlrpc, or post by
email. The data for the post is stored in $_POST, $_GET or the global
$post_data, depending on how the post was edited. For example, quick
edits use $_POST.Since this action is triggered right after the post has been saved,
you can easily access this post object by using get_post($post_id).
It takes 3 params:
- $post_ID
- WP_Post $post (post object)
- bool $update (whether this is an existing post being updated or not.)
Use this hook whenever you need to compare values before and after the
post update.This hook pass up to 3 arguments, as follows:
- $post_ID ;
- $post_after (post object after the update);
- $post_before (post object before the update);
So when should you use which one of them?
post_updated is fired up only if the given post existed before and currently is updated. It won’t get called, when a new post is inserted. It is very useful, if you want to do something with previous version of given post.
save_post is fired up whenever a post is saved. You don’t have easy access to previous version of given post in here (you’ll have to use revisions, if they’re available).
And some more confusion 😉
There is also one more action, you can use:
save_post_{$post->post_type}with the same params assave_post, it’s fired up just beforesave_postand you can use it, if you want to run your code only for given post type.