PHPでtxtファイルの内容を変更する方法

$fp = fopen("password.txt", "r");
if($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(&#39;文件存在&#39;);</script>";
}
else
{
   // echo "<script language=javascript>alert(&#39;文件不存在 $path&#39;);</script>";
}
$cbody = file($path);
//print_r($cbody);
$wifissid=$cbody[0];
$wifipwd=$cbody[1];
$wifissid=str_replace(&#39;wifiSSID=&#39;,&#39;&#39; ,$wifissid);//文本替换 将$wifissid值的wifiSSID替换为&#39; &#39;
$wifipwd=str_replace(&#39;wifiPWD=&#39;,&#39;&#39; ,$wifipwd);