How to Pass ID through Short Code

Question

Your short code function receives the attributes as the first argument:

function shortcode_function( $attributes ) {

Here $attributes is an array, and the attributes/values are inside that variable,

e.g. for [my-shortcode abc="123" xyz="789"]:

echo $attributes['abc']; // prints 123
echo $attributes['xyz']; // prints 789

You should also provide defaults and an opportunity to filter:

$attributes = shortcode_atts( [
    'id' => '',
], $attributes );

This way if the id is missing you don’t get PHP warnings, e.g. if we wrote [my-shortcode] by accident.

Improving The Shortcode

First, lets add type hints. This will avoid a common pitfall/bug that people fall into:

function shortcode_function( array $attributes ) : string {

Here we’ve told PHP that attributes is an array, and that this function returns a string, aka the content of our shortcode.

This give us:

function shortcode_function( array $attributes ) : string {
    // get the attributes
    $attributes = shortcode_atts( [
        'id' => 'default ID value goes here',
    ], $attributes );
    $id = $attributes['id'];

    // generate the shortcode's content:
    return 'My ID is:' . $id;
}
add_shortcode( 'my-shortcode', 'shortcode_function' );