Wordpress - Perform an action when post is updated/published

The save_post action fires When a post is updated and/or published -- including when a new post is inserted.

<?php
add_action( 'save_post', 'wpse41912_save_post' );
function wpse41912_save_post()
{
    // do stuff
}

If you want your functions to fire only when a post is being edited, you can hook into edit_post.

If you want it to fire when a post is moved from draft to publish you can hook into transition_post_status.

There are several actions you can use. For example:

• save_post
• edit_post
• publish_post
• etc.

While lesser-used, there are also post-status transition hooks.

the edit_post hook is probably the best hook... as it fires whenever a post/page is published or updated. save_post is another viable option... maybe better if you don't need it to fire when comments are updated.

http://codex.wordpress.org/Plugin_API/Action_Reference

the save_post page in the codex has an example of a function that fires whenever a post is saved:

http://codex.wordpress.org/Plugin_API/Action_Reference/save_post