Creating a function

function-documentation.php

<?php
 /**
  * Sends and email when a post is published.
  *
  * Sends and email using wp_mail standard WordPress function including data about 
  * the post being published.
  */

function-hooked-to-action.php

<?php
/**
 * Sends and email when a post is published.
 *
 * Sends and email using wp_mail standard WordPress function including data about 
 * the post being published.
 *
 * @param int     $ID   Post ID.
 * @param WP_Post $post Post object.
 */
function nelio_notify_on_post_published( $ID, $post ) {
  
  // Assemble the message.
  $message = 'Hi, a new post has been published. Here is the content:';
  $message .= $post->post_content;
  
  // Assemble the subject.
  $subject = '[New Post] ' . $post->post_title; 
     
  // Send the notification.
  wp_mail( 'recipient@example.com', $subject, $message );
  
}//end nelio_notify_on_post_published()

add_action( 'publish_post', 'nelio_notify_on_post_published', 10, 2 );

function-with-body.php

<?php
/**
 * Sends and email when a post is published.
 *
 * Sends and email using wp_mail standard WordPress function including data about 
 * the post being published.
 *
 * @param int     $ID   Post ID.
 * @param WP_Post $post Post object.
 */
function nelio_notify_on_post_published( $ID, $post ) {
  
  // Assemble the message.
  $message = 'Hi, a new post has been published. Here is the content:';
  $message .= $post->post_content;
  
  // Assemble the subject.
  $subject = '[New Post] ' . $post->post_title; 
     
  // Send the notification.
  wp_mail( 'recipient@example.com', $subject, $message );
  
}//end nelio_notify_on_post_published()

function-without-body.php

<?php
/**
 * Sends and email when a post is published.
 *
 * Sends and email using wp_mail standard WordPress function including data about 
 * the post being published.
 *
 * @param int     $ID   Post ID.
 * @param WP_Post $post Post object.
 */
function nelio_notify_on_post_published( $ID, $post ) {
  
}//end nelio_notify_on_post_published()