在.tpl中分配要在包含文件中分配的变量

I'm new to working with PHP smarty templating. I set up my original file in .php but I need to convert it to .tpl for a coworker to be able to edit it.

This was my original include statement, where I could manually set a variable for each page:

<?php 
    $meta_desc = "<meta name='description' content='This is my page meta description.'>";
    include "includes/document_head.php"; 
?>

This is my new code, but the variable isn't being set correctly:

{assign "meta_desc" "<meta name='description' content='This is my page meta description.'>"}
{% include file="includes/document_head.php" %}

What am I missing?

Your code is not correct. It should be this:

{assign var='meta_desc' value="<meta name='description' content='This is my page meta description.'>"}
{include file="includes/document_head.php"}