<?php
$content = file_get_contents('includes/app.php');
$content = str_replace(
    'available' => max(0, $base - $used),
            'price' => $item['price']
    ,
    'available' => max(0, $base - $used),
            'price' => $item['price'],
            'category_id' => $item['category_id'],
            'supplier_id' => $item['supplier_id'],
            'image_url' => $item['image_url'],
            'vat' => $item['vat']
    ,
    $content
);
file_put_contents('includes/app.php', $content);