how to customize wordpress internal functions, like adjacent_post_link()

Question

I need to customize the previous_post_link() and next_post_link() on WordPress.

Per example, I want to shrink permalinks like \"Top 5 programmi

Answer 1

To create a custom adjacent link for posts I can make use of the filter hook next_post_link and previos_post_link;

In the functions.php:

function shrink_previous_post_link($format, $link){
    $in_same_cat = false;
    $excluded_categories = '';
    $previous = true;
    $link='%title';
    $format='« %link';


    if ( $previous && is_attachment() )
        $post = & get_post($GLOBALS['post']->post_parent);
    else
        $post = get_adjacent_post($in_same_cat, $excluded_categories, $previous);

    if ( !$post )
        return;

    $title = $post->post_title;

    if ( empty($post->post_title) )
        $title = $previous ? __('Previous Post') : __('Next Post');

    $rel = $previous ? 'prev' : 'next';

    //Save the original title
    $original_title = $title;

    //create short title, if needed
    if (strlen($title)>40){
        $first_part = substr($title, 0, 23);
        $last_part = substr($title, -17);
        $title = $first_part."...".$last_part;
    }   

    $string = '';
    $link = str_replace('%title', $title, $link);   
    $link = $string . $link . '';

    $format = str_replace('%link', $link, $format);

    echo $format;   
}

function shrink_next_post_link($format, $link){
    $in_same_cat = false;
    $excluded_categories = '';
    $previous = false;
    $link='%title';
    $format='%link »';

    if ( $previous && is_attachment() )
        $post = & get_post($GLOBALS['post']->post_parent);
    else
        $post = get_adjacent_post($in_same_cat, $excluded_categories, $previous);

    if ( !$post )
        return;

    $title = $post->post_title;

    if ( empty($post->post_title) )
        $title = $previous ? __('Previous Post') : __('Next Post');

    $rel = $previous ? 'prev' : 'next';

    //Save the original title
    $original_title = $title;

    //create short title, if needed
    if (strlen($title)>40){
        $first_part = substr($title, 0, 23);
        $last_part = substr($title, -17);
        $title = $first_part."...".$last_part;
    }   

    $string = '';
    $link = str_replace('%title', $title, $link);   
    $link = $string . $link . '';

    $format = str_replace('%link', $link, $format);

    echo $format;   
}

add_filter('next_post_link', 'shrink_next_post_link',10,2);
add_filter('previous_post_link', 'shrink_previous_post_link',10,2);

That all I needed to do. Thanks!