To use this "how-to", you need to install phing in your machine.

I want to show you a little example that allow me to configure gii password and database informations, with phing.

First of all, when I start a new yii application, I copy protected/config/main.php in protected/config/main.php.dist, updating some field like ...:

'db' => array(
            'connectionString' => 'mysql:host=[[hostname]];dbname=[[database]]',
            'emulatePrepare' => true,
            'username' => '[[username]]',
            'password' => '[[password]]',
            'charset' => 'utf8',
        ),

I like also set gii configuration in this way:

'gii' => array(
            'class' => 'system.gii.GiiModule',
            'password' => '[[giipassword]]',
            'ipFilters' => array('127.0.0.1', '::1'),
        ),

Now, my config(.dist) file looks like this:

<?php

return array(
    'basePath' => dirname(__FILE__) . DIRECTORY_SEPARATOR . '..',
    'name' => 'YiiApp',
    'preload' => array(
        'log'
    ),
    'import' => array(
        'application.models.*',
        'application.components.*',
    ),
    'modules' => array(
        'gii' => array(
            'class' => 'system.gii.GiiModule',
            'password' => '[[giipassword]]',
            'ipFilters' => array('127.0.0.1', '::1'),
        ),
    ),
    'components' => array(
        'user' => array(
            'allowAutoLogin' => true,
        ),
        'db' => array(
            'connectionString' => 'mysql:host=[[hostname]];dbname=[[database]]',
            'emulatePrepare' => true,
            'username' => '[[username]]',
            'password' => '[[password]]',
            'charset' => 'utf8',
        ),
        'errorHandler' => array(
            'errorAction' => 'site/error',
        ),
        'log' => array(
            'class' => 'CLogRouter',
            'routes' => array(
                array(
                    'class' => 'CFileLogRoute',
                    'levels' => 'error, warning',
                ),
            ),
        ),
    ),
    'params' => array(
        'adminEmail' => 'webmaster@example.com',
    ),
);

Now I can create build.xml and put inside this content:

[xml]
<?xml version="1.0" encoding="UTF-8"?>
<project name="MyYiiApp" default="database">

    <target name="database" description="Configure database">
        <input propertyname="hostname" defaultValue="127.0.0.1"
                promptChar="?">Enter the hostname of db.</input>
        <input propertyname="database" defaultValue="database"
                promptChar="?">Enter the name of db.</input>
        <input propertyname="username" defaultValue="root"
                promptChar="?">Enter username to access to the db.</input>
        <input propertyname="password" defaultValue="root"
                promptChar="?">Enter password to access to the db.</input>
        <input propertyname="giipassword" defaultValue="giipassword"
                promptChar="?">Enter password to access to gii.</input>
        <copy file="protected/config/main.php.dist"
                tofile="protected/config/main.php" overwrite="true">
            <filterchain>
                <replacetokens begintoken="[[" endtoken="]]">
                    <token key="hostname" value="${hostname}" />
                    <token key="database" value="${database}" />
                    <token key="username" value="${username}" />
                    <token key="password" value="${password}" />
                    <token key="giipassword" value="${giipassword}" />
                </replacetokens>
            </filterchain>
        </copy>
    </target>

</project>

And now, I can run

$ phing

The output will be similar to this:

Buildfile: /var/www/yiiapp/build.xml:

Enter the hostname of db. [127.0.0.1]? 
Enter the name of db. [database]? yiiapp
Enter username to access to the db. [root]? 
Enter password to access to the db. [root]? 
Enter password to access to gii. [password]? 
     [copy] Copying 1 file to /var/www/yiiapp/protected/config
     [copy] Copying 1 file to /var/www/yiiapp/protected/config

BUILD FINISHED

As you can see, some questions will be asket to you. Your answers will be override main.php.dist file copying it into main.php. And you can install your application in this easy way. This is just a simple example.

You can also, for example, create your own console command and call them with phing.