Most Frequent WordPrees actions and shortcode

To follow this tutorial you need to know WordPress basics about plugins and shortcode.
Just replace the Hello Dolly plugin with this code:

<?php
/**
 * @package Hello_Dolly
 * @version 1.6
 */
/*
Plugin Name: Hello Dolly
Plugin URI: http://wordpress.org/extend/plugins/hello-dolly/
Description: This is not just a plugin, it symbolizes the hope and enthusiasm of an entire generation summed up in two words sung most famously by Louis Armstrong: Hello, Dolly. When activated you will randomly see a lyric from <cite>Hello, Dolly</cite> in the upper right of your admin screen on every page.
Author: Matt Mullenweg
Version: 1.6
Author URI: http://ma.tt/
*/

function after_closing_body_tag() {
 $c = 'after end body tag';
 echo "<div style='background-color:red;'>$c</div>";
}

function page_add ( $the_content ) {
 $before = "<h3>Before content from database</h3>";
 $after = ""; 
        if(is_single()){
       $after = "<h3>After content from database</h3>";
  }
 $new_content = $before.$the_content.$after;
 return $new_content;
}

function fs() {
 echo "<script>alert('from script in footer');</script>";
}

function head_script(){
 echo "<script>alert('from script in head tag');</script>";
} 
// Dont forget to embed shortcode in your post
function embed_shortcode( $atts ) {
 extract( shortcode_atts( array(
  'id' => ''
 ), $atts ) );

 $output = '<h3>' . $id . '</h3>';
 $output .= '<h3>' . get_permalink() . '</h3>';
 $output .= '<h3>' .  get_the_ID() . '</h3>'; 
 return $output;
}

add_action( 'wp_print_footer_scripts', 'fs' );

add_action('wp_head', 'head_script');

add_action( 'shutdown', 'after_closing_body_tag' );

add_shortcode( 'youtubevid', 'embed_shortcode' );

add_filter( 'the_content', 'page_add' );

?>

Note yellow highlighted portion of code. This is where we determine if post is alone on page or in archive.