How can I collect and output all attributes of all executed ShortCodes?

Question

I would like to collect all attributes of the shortcodes that are stored in a page in the ShortCodes and then output them all. I do these in a Plugin.

1.) Set a global Variable in init.php ==> $allShortcodeAtts = array();

2.) store atts in the global variable in the hook

function wpdocs_bartag_func( $atts ) {
 $atts = shortcode_atts( array(
    'foo' => 'no foo',
    'baz' => 'default baz'
 ), $atts, 'bartag' );
 global $allShortcodeAtts;
 $allShortcodeAtts[] = $atts;

 /* do other stuff */
 
 return "foo = {$atts['foo']}";
}

function register_shortcodes() {
   add_shortcode ( 'bartag', 'wpdocs_bartag_func' );
}
add_action ( 'init', 'register_shortcodes', 10 );

3.) Deposit shortcode in post_content => [bartag foo="bar1"] [bartag foo="bar2"]

4.) output all varaibles of the shortcodes

function after_register_shortcodes(){
 global $allShortcodeAtts;

 var_dump($allShortcodeAtts);
}
add_action ( 'init', 'after_register_shortcodes', 999 );

no attributes are stored in the global variables. I do not understand why?

Answer 1

Used shorcodes can be retrived only if they are added in post content (or any content saved in db). They can not be retrived if hardcoded in template files (TBH, they can, but that's not the issue here). This code can help you to get the shortcodes used in a post content.

function wpse387291_get_shortcodes() {
    global $post;
    
    $pattern = get_shortcode_regex();
    
    if (   preg_match_all( '/'. $pattern .'/s', $post->post_content, $matches ) {
        //$matches will hold the shortcodes if any
        echo '<pre>' . print_r( $matches, true ) . '</pre>';
    }
}
add_action( 'wp', 'wpse387291_get_shortcodes' );

You can use any hook that runs after wp.