Shorten excerpt in display posts shortcode

gistfile1.php

<?php

/**
 * Shorten excerpt in display posts shortcode
 * @author Bill Erickson
 * @link http://wordpress.org/extend/plugins/display-posts-shortcode/
 * @link http://www.billerickson.net/shortcode-to-display-posts/comment-page-1/#comment-4508
 *
 * @param $output string, the original markup for an individual post
 * @param $atts array, all the attributes passed to the shortcode
 * @param $image string, the image part of the output
 * @param $title string, the title part of the output
 * @param $date string, the date part of the output
 * @param $excerpt string, the excerpt part of the output
 * @return $output string, the modified markup for an individual post
 */

add_filter( 'display_posts_shortcode_output', 'be_customize_display_posts', 10, 6 );
function be_customize_display_posts( $output, $atts, $image, $title, $date, $excerpt ) {

	// First check if an excerpt is included by looking at the shortcode $atts
	if ( $atts['include_excerpt'] )
	
		// Now let's shorten the excerpt if needed
		$excerpt = '<p class="excerpt">' . be_truncate_phrase( get_the_excerpt(), 50 ) . '&hellip;</p>';
		
	else $excerpt = '';
	
	// Add a <p> around the title
	$title = '<p><a class="title" href="'. get_permalink() .'">'. get_the_title() .'</a></p>';

	// Pull in the custom field 'be_buy_button' that contains a shortcode
	global $post;
	$buy = get_post_meta( $post->ID, 'be_buy_button', true );

	// If buy isn't empty, wrap it in a <p> and do the shortcodes
	if ( !empty( $buy ) ) $buy = '<p class="buy">' . do_shortcode( $buy ) . '</p>'; else $buy = '';

	// Now let's rebuild the output. 
	$output = '<li>' . $image . $title . $date . $excerpt . $buy . '</li>';
	
	// Finally we'll return the modified output
	return $output;
}

/**
 * Truncate Excerpt
 *
 */
 
function be_truncate_phrase($phrase, $max_characters) {

	$phrase = trim( $phrase );

	if ( strlen($phrase) > $max_characters ) {

		// Truncate $phrase to $max_characters + 1
		$phrase = substr($phrase, 0, $max_characters + 1);

		// Truncate to the last space in the truncated string.
		$phrase = trim(substr($phrase, 0, strrpos($phrase, ' ')));
	}

	return $phrase;
}