<?php
preg_match('!/([^/]+)/[^/]*$!', 'http://w...content-available-to-author-only...w.example/test1/test2/test3/', $matches); echo $matches[1];
?>
PD9waHAKCgpwcmVnX21hdGNoKCchLyhbXi9dKykvW14vXSokIScsICdodHRwOi8vdy4uLmNvbnRlbnQtYXZhaWxhYmxlLXRvLWF1dGhvci1vbmx5Li4udy5leGFtcGxlL3Rlc3QxL3Rlc3QyL3Rlc3QzLycsICRtYXRjaGVzKTsKZWNobyAkbWF0Y2hlc1sxXTsKCj8+