php怎么修改txt文件内容

$fp = fopen("password.txt", "r");
if($fp)
{
     $pwd = fgets($fp);
}
else
{
     echo "打开文件失败";
}
fclose($fp);

$fp = fopen("password.txt", "w");//文件被清空后再写入
if($fp)
{
     $flag=fwrite($fp,$password);
     if(!$flag)
     {
          echo "写入文件失败<br>";
          break;
     }
}
fclose($fp);

$path="wifi_customer_settings.txt";
$body = file_get_contents($path);
if( file_exists( $path ) )
{
    $body = file_get_contents($path);//转为数组
//echo "<script language=javascript>alert('文件存在');</script>";
}
else
{
   // echo "<script language=javascript>alert('文件不存在 $path');</script>";
}
$cbody = file($path);
//print_r($cbody);
$wifissid=$cbody[0];
$wifipwd=$cbody[1];
$wifissid=str_replace('wifiSSID=','' ,$wifissid);//文本替换 将$wifissid值的wifiSSID替换为' '
$wifipwd=str_replace('wifiPWD=','' ,$wifipwd);

$path="wifi_customer_settings.txt";
$wifissid2=$_POST['wifissid'];
$wifipwd2=$_POST['wifipwd'];
$arr=array("wifiSSID=".$wifissid2,"\n","wifiPWD=".$wifipwd2);
$fp=fopen($path, 'w');
fputs($fp,$arr[0]);
fputs($fp,$arr[1]);
fputs($fp,$arr[2]);
fclose($fp);