check.php

<?php
/**
 * Created by PhpStorm.
 * User: shellus
 * Date: 2017/8/28
 * Time: 11:30
 */
$fd = fopen("pass.txt", "r");
// 如果php运行在linux，那么pass.txt里面的换行符用\n
// 如果php运行在windows，那就用\r\n
// 如果要固定用\n，那就把代码中的PHP_EOL换成"\n"

function check($pass){
    if (trim($pass) === "") return false;

    global $fd;
    while (($line = stream_get_line($fd, 1024, PHP_EOL)) !== false){
        if ($line === $pass){
            return true;
        }
    }
    return false;
}


if (check(@$_GET['pass'])){
    echo "1";
}else{
    echo "0";
}