PHP批量去除BOM头内容信息代码

<?php 
if (isset($_GET['dir'])){ //设置文件目录 
$basedir=$_GET['dir']; 
}else{ 
$basedir = '.'; 
} 
$auto = 1; 
checkdir($basedir); 
function checkdir($basedir){ 
if ($dh = opendir($basedir)) { 
while (($file = readdir($dh)) !== false) { 
if ($file != '.' && $file != '..'){ 
if (!is_dir($basedir."/".$file)) { 
echo "filename: $basedir/$file ".checkBOM("$basedir/$file")." <br>"; 
}else{ 
$dirname = $basedir."/".$file; 
checkdir($dirname); 
} 
} 
} 
closedir($dh); 
} 
} 
function checkBOM ($filename) { 
global $auto; 
$contents = file_get_contents($filename); 
$charset[1] = substr($contents, 0, 1); 
$charset[2] = substr($contents, 1, 1); 
$charset[3] = substr($contents, 2, 1); 
if (ord($charset[1]) == 239 && ord($charset[2]) == 187 && ord($charset[3]) == 191) { 
if ($auto == 1) { 
$rest = substr($contents, 3); 
rewrite ($filename, $rest); 
return ("<font color=red>BOM found, automatically removed._<a href=http://www.joyphper.net>http://www.joyphper.net</a></font>"); 
} else { 
return ("<font color=red>BOM found.</font>"); 
} 
} 
else return ("BOM Not Found."); 
} 
function rewrite ($filename, $data) { 
$filenum = fopen($filename, "w"); 
flock($filenum, LOCK_EX); 
fwrite($filenum, $data); 
fclose($filenum); 
} 
?> 

header("Content-type: text/html; charset=utf-8");