- var_dump: documentation ( source)
- preg_match: documentation ( source)
<?php
$articlecontent = "qwfasdasdqw\n:yeaaa323132[featuredimage]:asd\nWHAAAAT";
preg_match('/\[featuredimage\]:(.*)/', $articlecontent, $match);
var_dump($match);
if($match) {
echo $match[1];
} else {
echo "NO MATCH";
}