Get excerpt of string

get-excerpt.php

<?php
/**
 * Small utility function to get an excerpt. Standard length is 100 characters
 *
 * @param $string
 * @param int $start_postion
 * @param int $max_length
 *
 * @return string
 */
function get_excerpt( $string, $start_postion = 0, $max_length = 100 ) {
	if ( strlen( $string ) <= $max_length ) {
		return $string;
	}

	$excerpt    = substr( $string, $start_postion, $max_length - 3 );
	$last_space = strrpos( $excerpt, ' ' );
	$excerpt    = substr( $excerpt, 0, $last_space );
	$excerpt .= '...';

	return $excerpt;
}