Generate an excerpt from provided content. Strips HTML, removes trailing punctuation and adds a 'more' string when text has been removed.

excerpt.php

<?php

/**
 * Get an excerpt
 *
 * @param string $content The content to be transformed
 * @param int    $length  The number of words
 * @param string $more    The text to be displayed at the end, if shortened
 * @return string
 */
function get_excerpt( $content, $length = 40, $more = '...' ) {
	$excerpt = strip_tags( trim( $content ) );
	$words = str_word_count( $excerpt, 2 );
	if ( count( $words ) > $length ) {
		$words = array_slice( $words, 0, $length, true );
		end( $words );
		$position = key( $words ) + strlen( current( $words ) );
		$excerpt = substr( $excerpt, 0, $position ) . $more;
	}
	return $excerpt;
}