The say hello shortcode prints your display name and role if you're logged into a WordPress site. This is great if you need to know who you are logged in as and what role you have for any given post/page you're on.

say_hello_sc.php

<?php // Ignore this first line when copying to your child theme's functions.php file.

function say_hello_sc() {
    $u = wp_get_current_user();
    $display_name = $u->display_name ?: 'there';
    $roles = (array) $u->roles ?: ['not logged in'];
    return '<p>Yo, <strong>' . $display_name . '</strong> (<em>' . $roles[0] . '</em>)' . '. Thanks for stopping by ;-)</p>';
}
add_shortcode('say_hello', 'say_hello_sc');
/**
 * Usage: [say_hello]
 * 
 * Example output:
 *
 * Yo, Batman (administrator). Thanks for stopping by ;-)
 */

/**
 * More field examples:
 * $u = get_user_by( 'id', $user_id ); // Can do this for a specific user ID.
 * echo $u->user_login;
 * echo $u->first_name . ' ' . $u->last_name;
 * 
 * Reference: https://developer.wordpress.org/reference/classes/wp_user/
 */