- var_dump: documentation ( source)
- preg_match_all: documentation ( source)
<?php
$matches=array();
$string = 'This is a [templateVar]';
preg_match_all("/^[a-z]*@[a-z]*[.[a-z]{2}?.[a-z]{2}]?[.[a-z]{3}]?/", "usde@dev.com", $matches);
var_dump($matches);