CentOS下运行命令：
pear channel-update pear.php.net
出现错误：
-bash: pear: command not found
说明你安装php时没有把pear编译进去，只好去官方网站http://pear.php.net。
官方提供了两种方式安装pear：
1. 编译php的时候加入pear配置模块。
2. go-pear方式。
我尝试了go-pear方式。
下载go-pear脚本
wget http://pear.php.net/go-pear
重命名：
mv go-pear go-pear.php
执行脚本：
php go-pear.php
显示
Welcome to go-pear!
Go-pear will install the 'pear' command and all the files needed by
it. This command is your tool for PEAR installation and maintenance.
Go-pear also lets you download and install the following optional PEAR
packages: PEAR_Frontend_Web-beta, PEAR_Frontend_Gtk2, MDB2.
If you wish to abort, press Control-C now, or press Enter to continue:
回车确认。
HTTP proxy (http://user:password@proxy.myhost.com:port), or Enter for none::
回车不需要代理。
Below is a suggested file layout for your new PEAR installation. To
change individual locations, type the number in front of the
directory. Type 'all' to change all of them or simply press Enter to
accept these locations.
1. Installation prefix ($prefix) : /usr/local/ara
2. Temporary files directory : $prefix/temp
3. Binaries directory : $prefix/bin
4. PHP code directory ($php_dir) : $prefix/PEAR
5. Documentation base directory : $php_dir/docs
6. Data base directory : $php_dir/data
7. Tests base directory : $php_dir/tests
1-7, 'all' or Enter to continue:
安装配置，选择一项修改默认值，直接回车不修改。我要改安装目录，选了1，回车。
Installation prefix ($prefix) [/usr/local/ara] :
输入目录：
/usr/loacl/pear
然后开始安装了，最后会让提示你需要修改php.ini文件，确认即可。
安装完毕，有提示：
The 'pear' command is now at your service at /usr/local/pear/bin/pear
** The 'pear' command is not currently in your PATH, so you need to
** use '/usr/local/pear/bin/pear' until you have added
** '/usr/local/pear/bin' to your PATH environment variable.
你可以把/usr/local/pear/bin/pear加入PATH环境变量，或者直接使用/usr/local/pear/bin/pear运行pear命令。
/usr/local/pear/bin/pear channel-update pear.php.net
/usr/local/pear/bin/pear install HTML_Template_Sigma
这两个命令执行ok。
