include_php Smarty

Technical Note: include_php is pretty much deprecated from Smarty, you can accomplish the same functionality
via a custom template function. The only reason to use include_php is if you really have a need to quarantine the
php function away from the plugin directory or your application code. See the componentized template example
for details.
include_php tags are used to include a php script in your template. If security is enabled, then the php script must be located
in the $trusted_dir path. The include_php tag must have the attribute "file", which contains the path to the included php file,
either relative to $trusted_dir, or an absolute path.
include_php is a nice way to handle componentized templates, and keep PHP code separate from the template files. Lets say
you have a template that shows your site navigation, which is pulled dynamically from a database. You can keep your PHP
logic that grabs database content in a separate directory, and include it at the top of the template. Now you can include this
template anywhere without worrying if the database information was assigned by the application before hand.
By default, php files are only included once even if called multiple times in the template. You can specify that it should be
included every time with the once attribute. Setting once to false will include the php script each time it is included in the
template.
You can optionally pass the assign attribute, which will specify a template variable name that the output of include_php will
be assigned to instead of displayed.
The smarty object is available as $this within the PHP script that you include.
Example 7.9. function include_php 　
load_nav.php
-------------
<?php
// load in variables from a mysql db and assign them to the template
require_once("MySQL.class.php");
$sql = new MySQL;
$sql->query("select * from site_nav_sections order by name",SQL_ALL);
$this->assign('sections',$sql->record);
?>
index.tpl
---------
{* absolute path, or relative to $trusted_dir *}
{include_php file="/path/to/load_nav.php"}
{foreach item="curr_section" from=$sections}
<a href="{$curr_section.url}">{$curr_section.name}</a><br>
{/foreach}