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I'm looking for a plugin or example of code that can intercept the save/publish event and verify that all external links within the post content have rel="nofollow" attributes.

Is it possible to use add_filter or add_action on the post save/publish event?

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up vote 2 down vote accepted

I would try "wp_insert_post_data" filter.

add_filter('wp_insert_post_data', 'new_content' );
function new_content($content) {    
    for ( $i = 0; $i <= sizeof($matches[0]); $i++){

        if ( !preg_match( '~nofollow~is',$matches[0][$i]) ){
            $result = trim($matches[0][$i],">");
            $result .= ' rel="nofollow">';
            $content['post_content'] = str_replace($matches[0][$i], $result, $content['post_content']);


    return $content;

Obviously needs work, just a PoC.

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@Backie Please explain how exactly you would try to use the wp_insert_post_data filter? – EAMann Jan 21 '11 at 4:25
@EAMann added a little snippet of code. – Backie Jan 21 '11 at 12:35
@Backie, this works great, esp for a POC. Two comments: (1) How to alter the preg_match so that it skips over internal links? (2) Would there be an advantage to using "wp_insert_post_data" vs "content_save_pre"? – Scott B Jan 25 '11 at 16:41
backie.org/2011/01/25/… does it for external only. Only a simple change made. I wasn't able to get content_save_pre filter to work. I may have been doing it wrong tho. – Backie Jan 25 '11 at 18:38
@Backie: Just commented on your solution. Works great. Only suggestion would be to place the rel at the end of the attrib list vs at the beginning... – Scott B Jan 25 '11 at 19:55

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