str_replace (or another option) for replacing content located inside a php document -

i'm attempting make template file cms i'm making template file can contain variables {username} regular text replaced when page gets included on index.php page.

example: index page:

<?php include('templates/123/index.php'); ?> 

templates/123/index.php page

<?php include('header.php'); ?> welcome {username} <?php include('footer.php'); ?> 

i've tried several methods; however, run problems because page i'm trying change content on includes php code. every method try either 1) messes because opening , closing of php tags within document or 2) echoes out php code in document. there way can still achieve this? maybe class of kind? want able achieve safely.

i using custom variables {content1} replaces php code ioncubed retrieves data database content located in column1, same {column2} {column3} , {column4}. i'm trying make creation of templates extremely easy. (so i'd make code work well)

my preferred method of doing stuff involves starting code with:

ob_start(function($c) {     $replacements = array(         "username"=>"kolink",         "rank"=>"awesome"     );     return preg_replace_callback("/{(\w+)}/",function($m) use ($replacements) {         return isset($replacements[$m[1]]) ? $replacements[$m[1]] : $m[0];     },$c); });