is_readable

说明

bool is_readable ( string filename )

如果文件存在并且可读则返回 TRUE。

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。

例子 1. is_writable() 例子
<?php $filename = 'test.txt'; if (is_readable($filename)) { echo 'The file is readable'; } else { echo 'The file is not readable'; } ?>

注: 本函数的结果会被缓存。更多信息参见 clearstatcache()。

提示: 自 PHP 5.0.0 起本函数也可被某些 URL wrapper 使用。参考附录 L 来看哪些 wrapper 支持 stat() 系列函数的功能。

参见 is_writable()，file_exists() 和 fgets()。

add a note User Contributed Notes

jo at durchholz dot org
31-Jan-2006 01:15


DrTebi at yahoo dot com is wrong. is_readable() checks whether you can do file_get_contents() or similar calls, no more, no less. If the location given returns a 500 or 403 error, you can still read() that (you'll simply get the error page), but it's still read()able. Using is_readable to check the validity of a URL is simply the wrong function.

DrTebi at yahoo dot com
14-Oct-2005 12:22


Be careful when using is_readable on symbolic links.



is_readable will return true if the file the symbolic link is pointing to is readable.



The problem is that if the server does NOT allow to follow symbolic links, is_readable will still return true, but e.g. redirecting to the sybolic link will not work. For Apache, make sure that at the server, virtual host configuration level, or inside a directory container you have set

Options +FollowSymLinks



As an example, let's say you have at the document root directory:

index.php -- the script using is_readable

my_linked_page.html -- a regular HTML page

my_link -- a link pointing to my_linked_page.html



Now in index.php:

<?php

if (is_readable('my_link')) {

  header('Location: /my_link');

}

?>



If FollowSymLinks is forbidden, this will not work, if allowed, it will.

27-Jul-2005 10:08


Sometimes in situations where file_exists fails (returns false even though the file does exist) stat will work.

php dot 5 dot ce at spamgourmet dot com
12-Jan-2005 10:32


If you are using ACL, watch out for Bug #30931 (now open without any reaction for about 2 month, alltough an solution exists.)

takeda at takeda dot tk
07-Jun-2003 12:36


this function also can be used if you want check permissions for directory.

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