为何crontab -e不能执行fwrite写入文件？蹦溃了

function Write_FileFun_new($filename,$filedir, $htmldata = '') {<br />	if(!is_dir($filedir)) {<br />		mkdir($filedir, 0777);<br />	}<br />	$htmlfile = $filedir.$filename;<br />	if($fp = fopen($htmlfile, 'wbt')) {<br />		fwrite($fp,$htmldata);<br />		fclose($fp);<br />	} else {<br />		echo "<center><p>can not write to files, please check directory $htmldir.</p>
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                </center>";<br />		exit;<br />	}<br />}<br />$testnum_temp="<?php \$testnum = ".(intval($testnum)+1)."; ?>";<br />Write_FileFun_new("test.php","inc/", $testnum_temp);