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# CLIV. xattr Functions

# 简介

The xattr extension allows for the manipulation of extended attributes on a filesystem.

# 需求

To use xattr, you will need libattr installed. It is available at http://oss.sgi.com/projects/xfs/.

> 注: These functions only work on filesystems that support extended attributes, and have them enabled at mount time. Some common filesystems that support extended attributes are ext2, ext3, reiserfs, jfs, and xfs.

# 安装

xattr is currently available through PECL http://pecl.php.net/package/xattr.

If PEAR is available on your *nix-like system you can use the pear installer to install the xattr extension, by the following command: pear -v install xattr.

You can always download the tar.gz package and install xattr by hand:

例子 1. xattr install by hand

    gunzip xattr-xxx.tgz
    tar -xvf xattr-xxx.tar
    cd xattr-xxx
    phpize
    ./configure && make && make install

# 预定义常量

以下常量由本扩展模块定义，因此只有在本扩展模块被编译到 PHP 中，或者在运行时被动态加载后才有效。

`XATTR_ROOT` (integer)

  Set attribute in root (trusted) namespace. Requires root privileges.

`XATTR_DONTFOLLOW` (integer)

  Do not follow the symbolic link but operate on symbolic link itself.

`XATTR_CREATE` (integer)

  Function will fail if extended attribute already exists.

`XATTR_REPLACE` (integer)

  Function will fail if extended attribute doesn't exist.

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