Get all variables used in a php file

vars.php

<?php
/**
 * Find all the `$variables` in a given PHP file
 * @var string $path to a php file
 * @return string[] list of variable (not including the "$")
 */
function dk_get_vars_in_file($path) {
    $php_code = file_get_contents($path);
    $known_tokens = [];
    foreach(token_get_all($php_code) as $token) {
        $token = $token[1];
        if ('$' === substr($token,0,1)) {
            $known_tokens[] = str_replace('$','',$token);
        }
    }
    return $known_tokens;
}