php模拟cron

<?php
$needH = 15;//小时
$needM = 43;//分钟

while(true){
    $curH = intval(date('H'));
    $curM = intval(date('i'));
    if ($curH == $needH && $curM == $needM) {
        echo 'Begin~';
        for($i = 0; $i < 20; $i++) {
           exec("/home/temp/php/bin/php /home/temp/wujian/dump/gensql_stuCourseBatch.php 0 >/dev/null &");
        } 
        break;
    } 
    usleep(10000000);//万分之一秒
}

// nohup php file >/dev/null 2>&1 &