Secretly passing post ID/title etc into a shortcode form automatically to link submission to post

Question

A plugin shortcode displays a form underneath each post. Within the form thus displayed, there are numerous visible fields to be filled by users. There is also a hidden field to update a meta key visible on the back end only, with a place for value - as in image. I want to secretly pass the ID of the post (or title or name or slug etc) under which the form (by shortcode) is appearing, so I know at least where the form was even filled from.

Please consider modulating your solution so it can be understood by a beginner. (My question history shows)

I've tried a number of ways of using $post variable for the last 20 days - assuming its super global, using hooks, but a new session when submitting the form means I couldn't access the post data... either in functions.php file or the plugin PHP files - likewise sending data through PHP POST method seems like over exertion (it also places an extra submit button).

Im so lost for direction now!

I have access to $post in the Loop, on the individual post displayed - but I want any of the post attributes (ID/title/slug etc) to automatically STUFF into that one field when someone hits submit !!!?

Note: since $post is inaccessible, none of these work when directly placed in the value field: $post->ID $post->ID post_id $postid $post_id {$postid} {$post_id} the_ID ID get_the_ID(); the_title(); get_queried_object_id()

Answer 1

If you put a unique placeholder value there, you can do a find/replace via the_content filter, which runs after the shortcode is rendered, but before the content is output in the template.

For example, this will replace any occurrence of replacethisthing with the post ID:

function wpd_replace_something_in_the_content( $content ){
    return str_replace( "replacethisthing", get_the_ID(), $content );
}
add_filter( 'the_content', 'wpd_replace_something_in_the_content', PHP_INT_MAX );