php如何修改本地文件

//txt文件中只有一行数据 读
$fp = fopen("password.txt", "r");
if($fp)
{
     $pwd = fgets($fp);
}
else
{
     echo "打开文件失败";
}
fclose($fp);

//txt文件中只有一行数据 写
 1 $fp = fopen("password.txt", "w");//文件被清空后再写入
 2 if($fp)
 3 {
 4      $flag=fwrite($fp,$password);
 5      if(!$flag)
 6      {
 7           echo "写入文件失败<br>";
 8           break;
 9      }
10 }
11 fclose($fp);

//txt文件中有多行数据  读 以数组的形式
 1 $path="wifi_customer_settings.txt";
 2 $body = file_get_contents($path);
 3 if( file_exists( $path ) )
 4 {
 5     $body = file_get_contents($path);//转为数组
 6 //echo "<script language=javascript>alert('文件存在');</script>";
 7 }
 8 else
 9 {
10    // echo "<script language=javascript>alert('文件不存在 $path');</script>";
11 }
12 $cbody = file($path);
13 //print_r($cbody);
14 $wifissid=$cbody[0];
15 $wifipwd=$cbody[1];
16 $wifissid=str_replace('wifiSSID=','' ,$wifissid);//文本替换 将$wifissid值的wifiSSID替换为' '
17 $wifipwd=str_replace('wifiPWD=','' ,$wifipwd);

//txt文件中有多行数据 写  以数组的形式
1 $path="wifi_customer_settings.txt";
2 $wifissid2=$_POST['wifissid'];
3 $wifipwd2=$_POST['wifipwd'];
4 $arr=array("wifiSSID=".$wifissid2,"\n","wifiPWD=".$wifipwd2);
5 $fp=fopen($path, 'w');
6 fputs($fp,$arr[0]); 
7 fputs($fp,$arr[1]);
8 fputs($fp,$arr[2]);
9 fclose($fp);