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I would like to run a filter on post content after it has been created or updated.

I would like this to occur after the user has submitted the post, as it may be a bit of a lengthy process (a find/replace to search for glossary terms and replace them with links).

What's the most efficient and reliable way to achieve this?

Thanks in advance,

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    Does this have to occur immediately on publish? Or could it occur...say...once every hour or something like that? Commented Feb 17, 2012 at 15:26
  • That would be absolutely fine :) Commented Feb 17, 2012 at 15:44

3 Answers 3

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Alright, here's some code I just whipped up. Completely untested, just wrote it right off the cuff...so don't expect it to work 100% when you drop it in, but the core concept is there, as is a decent amount of the legwork

add_action( 'my_filter_posts_content', 'my_filter_content' ); add_action( 'save_post', 'my_set_content_filter' ); if( !wp_next_scheduled( 'my_filter_posts_content' ) ) { wp_schedule_event( time(), 'hourly', 'my_filter_posts_content' ); } function my_filter_content() { //check to see if posts need to be parsed if( get_option( 'my_updated_posts' ) == false ) return false; //parse posts $ids = unserialize( get_option( 'my_updated_posts' ) ); foreach( $ids as $v ) { YOUR_FUNCTION_HERE( $v ); } //make sure no values have been added while loop was running $id_recheck = unserialize( get_option( 'my_updated_posts' ) ); my_close_out_filter( $ids, $id_recheck ); /* once all options, including any added during the running of what could be a long cronjob are done, remove the value and close out */ delete_option( 'my_updated_posts' ); return true; } function my_set_content_filter( $post_id ) { //get the previous value $ids = unserialize( get_option( 'my_updated_posts' ) ); //add new value if necessary if( !in_array( $post_id, $ids ) ) { $ids[] = $post_id; update_option( 'my_updated_posts', serialize( $ids ) ); } } function my_close_out_filter( $beginning_array, $end_array ) { $diff = array_diff( $beginning_array, $end_array ); if( !empty ( $diff ) ) { foreach( $diff as $v ) { YOUR_FUNCTION_HERE( $v ); } } my_close_out_filter( $end_array, unserialize( get_option( 'my_updated_posts' ) ) ); }
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  • Thanks for that, I'll give it a go now. Is YOUR_FUNCTION_HERE( $v ); where I'd put my filtering code? Commented Feb 17, 2012 at 16:17
  • Yup, you've got it...let me know how that works, I'm interested as to what stupid error(s) I made :D Commented Feb 17, 2012 at 16:19
  • You know...thinking about it, I bet you could do some pretty powerful filtering if you based a class off that code... Commented Feb 17, 2012 at 16:23
  • One thing.. how do I go about seeing whether or not the cron job has actually been scheduled? Commented Feb 17, 2012 at 16:26
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    There are plugins that will do that for you, I think Cron View is the one that I use, but I cannot remember. Commented Feb 17, 2012 at 16:44
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Please see my answer here. It's a proof-of-concept for running a native crontab in Linux with your WP installation.

As for WP-Cron functionality, beware of these caveats:

  • WP-Cron is a pseudo cron that is runs when WP is loaded. WP checks if a WP-Cron is scheduled or behind schedule to run and then executes the cron script.
  • If there is not adequate traffic, your cron might run really late.
  • Scheduling a WP-Cron to run during peak hours might cause some performance issues if it's a large, intensive script.

If you choose to go the WP-Cron route, here's a great article to show you how to use it. You can also check out the WP functions in the Codex here.

I prefer the reliability of a Linux crontab, especially for integral, heavy-weight cron scripts. For extremely lightweight scripts, I do use WP-Cron at times.

Hope this helps!

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  • Hi Brian. I was under the impression that WP had built-in features for setting up cron jobs? Commented Feb 17, 2012 at 16:15
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    Well, it's a psuedo-cron which depends on people visiting your site. It could create a performance issue for the unlucky user who hits your site when it's time to run the wp-cron. The more reliable approach to make sure the cron runs at scheduled intervals is to use crontab. You can see the wp-cron functions here: codex.wordpress.org/Category:WP-Cron_Functions Commented Feb 17, 2012 at 16:22
  • Thanks Brian. Site gets enough traffic (30,000 unique visitors/week) so I think we'll be OK in those terms. The script isn't absolutely massive and there'll very rarely be more than one post at a time updated. Commented Feb 17, 2012 at 16:33
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Would the save_post action work for you?

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

You might also consider edit_post or publish_post

You can view other actions in the Codex

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  • Hi Kyle. Thanks, I understand the workings of save_post :) What I'm trying to do is run this filter in the background. If I run the filter on save_post, it'll take quite some time for the post to save, which is an annoyance for my authors that I'd like to avoid. Commented Feb 17, 2012 at 16:09
  • Oh, gotcha. Didn't realize the background requirement. Commented Feb 17, 2012 at 16:13

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