Add author info to WordPress blog post using a shortcode

post-author.php

<?php
//add any of the following shortcode functions to your theme's functions.php file

//display the author name which is linked to the About page
function author_name_shortcode(){
    global $post;
    $post_id = $post->ID;
    $author = get_the_author($post_id);
    $linkedAuthor = "<a href='/about'>".$author."</a>";
    return $linkedAuthor;
}
add_shortcode('post_author','author_name_shortcode');

//display the post's last modified date
function post_updated_shortcode(){
    global $post;
    $post_id = $post->ID;
    $mod_date = get_the_modified_date('F jS, Y', $post_id);
    return $mod_date;
}
add_shortcode('post_updated','post_updated_shortcode');

//display the author AND last modified date
function post_credits_shortcode(){
    global $post;
    $post_id = $post->ID;
    $mod_date = get_the_modified_date('F jS, Y', $post_id);
    $author = get_the_author($post_id);
    $linkedAuthor = "<a href='/about'>".$author."</a>";
    $post_creds = $linkedAuthor." | ".$mod_date;
    return $post_creds;
}
add_shortcode('post_credits','post_credits_shortcode');