php variable

hi, i am using the blog app

for my pages, the header is written in a separate php file and for the page title, i use this syntax:

<title><?=($pageTitle == "") ? "" : "$pageTitle"?></title>

in every page, i set some variables at the beginning, like this:

<?php
$pageTitle      = "";
$Description    = "";
include ("${Root}_header.php");
?>

my question is: how can i change the header for the blog pages

<title><?php perch_blog_post_field(perch_get('s'), 'postTitle'); ?> - Blog Example</title>

i neet to transfer the postTitle in the variable for my pageTitle

can you help out ?

thank you! katja