From [[http://www.phpsnaps.com/snaps/view/get-excerpt-from-string/]]\\

<code>
<?php

/**
 * Get excerpt from string
 * 
 * @param String $str String to get an excerpt from
 * @param Integer $startPos Position int string to start excerpt from
 * @param Integer $maxLength Maximum length the excerpt may be
 * @return String excerpt
 */
function getExcerpt($str, $startPos=0, $maxLength=100) {
 if(strlen($str) > $maxLength) {
  $excerpt   = substr($str, $startPos, $maxLength-3);
  $lastSpace = strrpos($excerpt, ' ');
  $excerpt   = substr($excerpt, 0, $lastSpace);
  $excerpt  .= '...';
 } else {$excerpt = $str;}

return $excerpt;
}
?>
</code>