Very simple template "engine"

simple-template.php

<?php
function render($template, $vars) {
    return \preg_replace_callback("!{{\s*(?P<key>[a-zA-Z0-9_-]+?)\s*}}!", function($match) use($vars){
        return isset($vars[$match["key"]]) ? $vars[$match["key"]] : $match[0];
    }, $template);
}