How to filter post content during publish/save routine with str_ireplace()?

Question

I'm trying to create a function that does a text replacement on the post content when its saved (the_content).

The stub function is below, but how do I obtain a reference to the post content, then return the filtered content back to the "publish_post" routine?

However, my replacement is either not working and/or not passing the updated post_content to the publish function. The values never get replaced.

function my_function() {
    global $post;
    $the_content = $post->post_content;
    $text = " test ";
    $post->post_content = str_ireplace($text, '<b>'.$text.'</b>', $the_content  );
    return $post->post_content;
    }
add_action('publish_post', 'my_function');

Answer 1

Probably easier to do something like this:

function my_function($post) {
  $content = str_ireplace(" test ", '<b>'.$text.'</b>', $post->content);

  return $content;
}

Less focus was on the interior of the function, but the idea is that you pass the object to the function in the () then call the directly rather than globalizing the value. It should be more direct that way.

Answer 2

the passed variable here is $id. This should work:

function my_function($id) {
  $the_post = get_post($id);
  $content = str_ireplace(" test ", '<b>'.$text.'</b>', $the_post->post_content);

  return $content;
}
add_action('publish_post', 'my_function');