$re = '/(?:(?:.*?\|\s?){6}.*::)(.+?)(?:(?=\.?\s?$)|(?=\s?\.?\|))/i';
$str = '[String1] | [String two is here] ||| String 3 | String-4 | String::5';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php