is_writable()

(PHP 4, PHP 5, PHP 7)

判断给定的文件名是否可写

说明

如果文件存在并且可写则返回TRUE。$filename参数可以是一个允许进行是否可写检查的目录名。

记住 PHP 也许只能以运行 webserver 的用户名（通常为'nobody'）来访问文件。不计入安全模式的限制。

参数

要检查的文件名称。

返回值

如果文件$filename存在并且可写则返回TRUE。

范例

Example #1is_writable()例子

错误／异常

失败时抛出E_WARNING警告。

注释

Note:此函数的结果会被缓存。参见clearstatcache()以获得更多细节。

自 PHP 5.0.0 起,此函数也用于某些URL 包装器。请参见支持的协议和封装协议以获得支持stat()系列函数功能的包装器列表。

参见

• is_readable() 判断给定文件名是否可读
• file_exists() 检查文件或目录是否存在
• fwrite() 写入文件（可安全用于二进制文件）

Be warned, that is_writable returns false for non-existent files, although they can be written to the queried path.

Check director is writable recursively. to return true, all of directory contents must be writable 

Regarding you might recognize your files on your web contructed by your PHP-scripts are grouped as NOBODY you can avoid this problem by setting up an FTP-Connection ("ftp_connect", "ftp_raw", etc.) and use methods like "ftp_fput" to create these [instead of giving out rights so you can use the usual "unsecure" way]. This will give the files created not the GROUP NOBODY - it will give out the GROUP your FTP-Connection via your FTP-Program uses, too.
Furthermore you might want to hash the password for the FTP-Connection - then check out:
http://dev.mysql.com/doc/mysql/en/Password_hashing.html

To Darek and F Dot: About group permissions, there is this note in the php.ini file:
; By default, Safe Mode does a UID compare check when
; opening files. If you want to relax this to a GID compare,
; then turn on safe_mode_gid.
safe_mode_gid = Off

This file_write() function will give $filename the write permission before writing $content to it.
Note that many servers do not allow file permissions to be changed by the PHP user. 

It appears that is_writable() does not check full permissions of a file to determine whether the current user can write to it. For example, with Apache running as user 'www', and a member of the group 'wheel', is_writable() returns false on a file like
-rwxrwxr-x      root     wheel     /etc/some.file

The results of this function seems to be not cached :
Tested on linux and windows 

In response to Darek:
We have two servers: one running PHP 5.0.4 and Apache 1.3.33, the other running PHP 4.3.5 and Apache 1.3.27. The PHP 4 server exhibits the behavior you are describing, with is_writable() returning 'false' even though the www user is in the group that owns the file, but the PHP 5 server is returning 'true.'

Check if a directory is writable. Work also on mounted SMB shares:
function isWritablePath($home, $xpath) {
  $isOK = false;
  $path = trim($xpath);
  if ( ($path!="") && (strpos($path,$home)!==false) && is_dir($path) && is_writable($path) ) {
    $tmpfile = "mPC_".uniqid(mt_rand()).'.writable';
    $fullpathname = str_replace('//','/',$path."/".$tmpfile);
    $fp = @fopen($fullpathname,"w");
    if ($fp !== false) {
      $isOK = true;
    }
    @fclose($fp);
    @unlink($fullpathname);
  }
  return $isOK;
  
}

This is the latest version of is__writable() I could come up with.
It can accept files or folders, but folders should end with a trailing slash! The function attempts to actually write a file, so it will correctly return true when a file/folder can be written to when the user has ACL write access to it. 

Since looks like the Windows ACLs bug "wont fix" (see http://bugs.php.net/bug.php?id=27609) I propose this alternative function:

It should work both on *nix and Windows
NOTE: you must use a trailing slash to identify a directory

function is_writable('ftp://user.....') always return false. I can create/delete files, but can check is writable. Is this bug or php feature :)?

I'd like to also clarify a point on this. Even if you see 777 permissions for the directly, you may need to check your ACL, since your server's group might not have write permissions there.

Under Windows, it only returns the read-only attribute status, not the actual permissions (ACL).
See http://bugs.php.net/bug.php?id=27609

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