(PECL xattr >= 0.9.0)
xattr_get — Get an extended attribute
This function gets the value of an extended attribute of a file.
扩展的属性有两个不同的名字空间：user 和 root 名字空间。user 名字空间对所有用户均有效，而 root 名字空间仅对拥有 root 权限的用户有效。xattr 默认在 user 名字空间上进行操作，但是可以使用 flags 参数进行更改。
The file from which we get the attribute.
The name of the attribute.
| XATTR_DONTFOLLOW | Do not follow the symbolic link but operate on symbolic link itself. |
| XATTR_ROOT | Set attribute in root (trusted) namespace. Requires root privileges. |
Returns a string containing the value or FALSE if the attribute doesn't exist.
Example #1 Checks if system administrator has signed the file
<?php
$file = '/usr/local/sbin/some_binary';
$signature = xattr_get($file, 'Root signature', XATTR_ROOT);
/* ... check if $signature is valid ... */
?>