(PECL xattr >= 0.9.0)
xattr_set — Set an extended attribute
This function sets 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 in which we set the attribute.
The name of the extended attribute. This attribute will be created if it doesn't exist or replaced otherwise. You can change this behaviour by using the flags parameter.
The value of the attribute.
| XATTR_CREATE | Function will fail if extended attribute already exists. |
| XATTR_REPLACE | Function will fail if extended attribute doesn't exist. |
| 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. |
如果成功则返回 TRUE，失败则返回 FALSE。
Example #1 Sets extended attributes on .wav file
<?php
$file = 'my_favourite_song.wav';
xattr_set($file, 'Artist', 'Someone');
xattr_set($file, 'My ranking', 'Good');
xattr_set($file, 'Listen count', '34');
/* ... other code ... */
printf("You've played this song %d times", xattr_get($file, 'Listen count'));
?>