How to reindex data with shell_exec cron magento

[magentolavlesh]

$indexer="/var/www/clients/client1/web38/web/shell/indexer.php";  
if(file_exists($indexer))  
{  
                $idxlist=array("catalog_product_attribute",  
                               "catalog_product_price",  
                               "catalog_product_flat",  
                               "catalog_category_flat",  
                               "catalog_category_product",  
                               "catalog_url",  
                               "catalogsearch_fulltext",  
                               "cataloginventory_stock");  
        //reindex using magento command line  
        foreach($idxlist as $idx)  
        {  
            echo "reindex $idx \n ";  
            shell_exec("php /var/www/clients/client1/web38/web/shell/indexer.php --reindex $idx"); 

exec("php /var/www/clients/client1/web38/web/shell/indexer.php --reindex $idx");

Re-indexing is not working with this way , what issue in my code , please tell me suggestion.