magento-remove_all_category.php

<?php 
/* Remove all category */
require_once('app/Mage.php');
ini_set('display_errors', 1);
set_time_limit(0);


Mage::setIsDeveloperMode(true);
Mage::app();
Mage::app()->setCurrentStore(Mage_Core_Model_App::ADMIN_STORE_ID);


$resource = Mage::getSingleton('core/resource');
$db_read = $resource->getConnection('core_read');

$categories = $db_read->fetchCol("SELECT entity_id FROM " . $resource->getTableName("catalog_category_entity") . " WHERE entity_id>2 ORDER BY entity_id DESC");
foreach ($categories as $category_id) {
	try {
		Mage::getModel("catalog/category")->load($category_id)->delete();
	} catch (Exception $e) {
		echo $e->getMessage() . "\n";
	}
}

exit;