- print_r: documentation ( source)
- preg_match_all: documentation ( source)
<?php
$re = '/(?:\[Links|\G(?!^))(?=[^][]*])\h+([^\s=]+)="([^\s"]+)"/m';
$str = '[Links label="my_label" url="my_url" external="other_value"]';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
print_r($matches);