<?php
$link = '13542345/essa_e_minhastring';
$pattern = '/[^\/]+/';
preg_match($pattern, $link, $partes, PREG_OFFSET_CAPTURE
); echo $partes[0][0]; // dá 13542345
PD9waHAKCiRsaW5rID0gJzEzNTQyMzQ1L2Vzc2FfZV9taW5oYXN0cmluZyc7CiRwYXR0ZXJuID0gJy9bXlwvXSsvJzsKcHJlZ19tYXRjaCgkcGF0dGVybiwgJGxpbmssICRwYXJ0ZXMsIFBSRUdfT0ZGU0VUX0NBUFRVUkUpOwplY2hvICRwYXJ0ZXNbMF1bMF07IC8vIGTDoSAxMzU0MjM0NQ==