Giving the_excerpt in the place of the_content?

Question

Short and sweet — I wanted to deliver up the excerpt of a post in the place of the_content on certain pages. Naturally, if no excerpt is present one would be generated from the content. I understand I can just go in and edit the theme files, but I'd like a less-invasive method.

Seeing how something like the following works:

add_action( 'the_content', 'myFunc' );
function myFunc ( $content ) {
  the_title();
}

I thought I would try this

add_action( 'the_content', 'myFunc' );
function myFunc ( $content ) {
  the_excerpt();
}

This. Fails. Gloriously. It results in a fatal error, actually:

FATAL ERROR: MAXIMUM FUNCTION NESTING LEVEL OF '100' REACHED, ABORTING! IN C:\WAMP\WWW\WORDPRESS\WP-INCLUDES\POST.PHP ON LINE 555

This is followed by a massive call stack, which appears to have been set into a mad frenzy of recursive calls.

Turning the Tables

So this got me curious, and I tried the opposite. Deliver the_content in the place of the_excerpt:

add_action( 'the_excerpt', 'myFunc' );
function myFunc ( $content ) {
  the_content();
}

This, to my surprise, worked just fine. So what I'm gathering is that the_excerpt calls the_content, but the_content doesn't call the_excerpt - this would certainly explain the fact that it works one way, but the other seems to be set off in a massive fit of recursion.

Not being very familiar with the inner-workings of these two function, I was curious what the community here could provide in way of insight. What's the problem with hooking into the_content and calling the_excerpt?

How can I achieve this effect if not by calling the_content directly? I understand that I could provide my own custom excerpt logic, but this would de-normalize the excerpt logic in my site, meaning I'd have some excerpts being created via custom code in the functions.php, and others created via the internal methods of WordPress - ideally, I would avoid this and use only the internal methods if possible.

Answer 1

All good examples. But they weren't working for me with the theme (pinboard) and plugin I was using (secondary-html-content) and what I wanted to do.

The first challenge was to make sure that I get both pieces of content instead of just one. The second challenge was to replace the excerpt on the homepage with the actual content.

So I created a new plugin that does this:

function okmAddingContentExcerpt() {
    global $post;
    $content = '<div class="comment-first">'.$post->post_content.'</div>';
    // Adia Review is the name of the label from secondary-html-content plugin
    $content .= '<div class="comment-second">'.get_secondary_content('Adia Review',$post->ID).'</div>';
    return $content;
}
add_filter('the_excerpt', 'okmAddingContentExcerpt');

function okmAddingContentSingle() {
    global $post;
    $content = '<div class="comment-first">'.$post->post_content.'</div>';
    // remove the filter so that it doesn't loop over and over
    remove_filter('the_content','okmAddingContentSingle');
    $content .= '<div class="comment-second">'.get_secondary_content('Adia Review',$post->ID).'</div>';
    return $content;
}
add_filter('the_content', 'okmAddingContentSingle');

Notice how I wanted to keep the content instead of the excerpt on the main page.

Oh yeah, if you want to download the plugin, I added it to my blog-site: http://okmaya.com/wordpress-plugin-for-pinboard-theme-and-secondary-html-content-plugin/

Answer 2

Actually, the_excerpt() calls get_the_excerpt(), which outputs $post->post_excerpt.

One thing, also: shouldn't you be using add_filter() instead of add_action()?

Why are you using the_excerpt()/the_content()/the_title(), rather than setting $content = get_the_excerpt() etc., and then returning $content? e.g. this:

add_filter( 'the_content', 'myFunc' );
function myFunc ( $content ) {
  the_excerpt();
}

...would normally be written as such:

add_filter( 'the_content', 'myFunc' );
function myFunc ( $content ) {
  $content = get_the_excerpt();
  return $content;
}

Not sure if any of that will address your problem of the recursive loop...

EDIT

Your last comment gave me an idea: why not just pass $content through wp_trim_excerpt() and be done with it?

add_filter( 'the_content', 'myFunc' );
function myFunc( $content ) {
    $excerpt = wp_trim_excerpt( $content );
    return $excerpt;
}

EDIT 2

Okay, I'm with you now. How about we roll our own excerpt function?

add_filter( 'the_content', 'myFunc' );
function myFunc( $content ) {
    $text = strip_shortcodes( $content );
    $text = str_replace(']]>', ']]>', $text);
    $text = strip_tags($text);
    $excerpt_length = apply_filters('excerpt_length', 55);
    $excerpt_more = apply_filters('excerpt_more', ' ' . '[...]');
    $words = preg_split("/[\n\r\t ]+/", $text, $excerpt_length + 1, PREG_SPLIT_NO_EMPTY);
    if ( count($words) > $excerpt_length ) {
         array_pop($words);
         $text = implode(' ', $words);
         $text = $text . $excerpt_more;
     } else {
         $text = implode(' ', $words);
     }        
     return $text;
}