[HNCTF 2022 Week1]Interesting_include

<?php
//WEB手要懂得搜索
//flag in ./flag.php

if(isset($_GET['filter'])){
    $file = $_GET['filter'];
    if(!preg_match("/flag/i", $file)){
        die("error");
    }
    include($file);
}else{
    highlight_file(__FILE__);
} 

直接php伪协议