Example PHP ...

gistfile1.php

<?php

    $customers = array('hennie' => 100, 'krzysztof' => 10);

    $customer = $_GET['customer'];

    if (! $customer)
    {
      echo 'You have to specify a customer name in order to access its balance details';
      exit(1);
    }

    if (array_key_exists($customer, $customers))
    {

        echo 'Customer ' . $customer . ' has balance: ' . $customers[$customer];
    }
    else
    {
        echo 'No such customer: ' . $customer;
    }
?>