Generate a custom excerpt in Wordpress.

Custom Excerpt.php

<?php

/**
 * Custom Excerpt
 *
 * @param  array  $args {
 *     Optional. Array of excerpt() arguments.
 *
 *     @type int    $limit   Limit result to amount. Default '55'.
 *     @type string $limitby Limit by either word or character. Default 'word'. Accepts 'char', 'word'.
 *     @type string $append  Append a string to the excerpt. Default null.
 *     @type string $source  Source to use for the excerpt. Default get_the_excerpt().
 * }
 * @return string $excerpt String of the resulting excerpt.
 *
 *    $excerpt = array(
 *        'limit'   => 55,
 *        'limitby' => 'char',
 *        'append'  => '...',
 *        'source'  => $source
 *    );
 *
 */
function excerpt($args = null) {
    $defaults = array(
        'limit' => 55,
        'limitby' => 'word',
        'append' => null,
        'source' => get_the_excerpt()
    );

    $args = wp_parse_args($args, $defaults);

    $excerpt = $args['source']; // Excerpt equal to $source argument
    $excerpt = strip_shortcodes($excerpt); // Strip shortcodes
    $excerpt = strip_tags($excerpt); // Strip tags
    $excerpt = str_replace(array('&nbsp;'), ' ', $excerpt); // Replace forced space with single space

    // Limit by character if excerpt length greater than limit
    if ($args['limitby'] == 'char' && strlen($excerpt) > $args['limit']) {
        $excerpt = preg_replace('(\[.*?\])', '', $excerpt);
        $excerpt = substr($excerpt, 0, $args['limit']);
        $excerpt = substr($excerpt, 0, strripos($excerpt, ' '));
        $excerpt = trim(preg_replace('/\s+/', ' ', $excerpt));
        $excerpt = $excerpt . $args['append'];
    // Limit by word if excerpt length greater than limit
    } else if ($args['limitby'] == 'word' && str_word_count($excerpt) > $args['limit']) {
        $excerpt = preg_replace('/\s+/', ' ', $excerpt); // Replace multiple spaces into single space
        $excerpt = explode(' ', $excerpt, $args['limit'] + 1);
        array_pop($excerpt);
        $excerpt = implode(' ', $excerpt);
        $excerpt = $excerpt . $args['append'];
    }

    return $excerpt;
}