How to add PHP code to .tpl file [duplicate]

Answer 1

There is a best practise guide on smarty homepage. #1 is Do not embed PHP!

http://www.smarty.net/best_practices

Try this: {include_php file="/path/to/somefile.php"}

But notice:

{include_php} is deprecated from Smarty, use registered plugins 
to properly insulate presentation from the application code. 
As of Smarty 3.1 the {include_php} tags are only available 
from SmartyBC.

So best way is to write a smarty plugin as explained by rodneyrehm