在没有刷新Bootstrap（3）模式的情况下捕获ajax响应url中的变量？

I have a login script and I am using bootstrap modal for login form. It works fine except i am unable to catch the value of a php var, this is sent as a response when the form is submitted.

http://localhost/clock/index.php?f=4

I would like to be able to catch value of f4 in my modal which I am not able to. how can i do this ?

Edited:

Javascript/Jquery code to send ajax request

$(document).ready(function(){
      $('#csignin').click(function(){
            $("#myModal-signin").modal('show');
        });

        $('#csignup').click(function(){
            $("#myModal-signup").modal('show');
        });


    $('#loginForm').on("submit", function (e) {

        e.preventDefault();
        //alert('submitting');
        $.ajax({
            type: "POST",
            url: 'usr/login_process.php',
            data: $('#loginForm').serialize(),
            dataType: 'text',
            timeout: 5000,
            success: function(data) {
                //success msg
                //alert(data);


                $(".signin-msg").html("<?php
                if (isset($_SESSION['f'])) {

                    switch ($_SESSION['f']) {
                        default: break;
                        case 0:
                            echo LOGIN_NOT_ACTIVE_USER;
                break;
            case 1:
                echo LOGIN_USER_BLOCKED;
                break;
            case 2:
                echo LOGIN_PASSWORDS_NOT_MATCHED;
                break;
            case 3:
                echo LOGIN_NO_TRIES;
                break;
            case 4:
                echo LOGIN_USER_INFO_MISSING;
                break;
            case 5:
                echo LOGIN_NOT_ACTIVE_ADMIN;
                break;
        }
    }


    ?>").css("color", "red");



            }
        });

    });

});

this is PHP code sends response to ajax call (http://localhost/clock/index.php?f=4)

if (isset($_POST['process'])) {
    // Try to login the user
    if ($qls->User->login_user()) {
        $qls->redirect($qls->config['login_redirect']);
    }
    else {
        $_SESSION['f']=$qls->User->login_error;
        $qls->redirect('../index.php?f=' . $qls->User->login_error);

    }
}
else {
    $qls->redirect('../index.php');
}

I would like to catch the var f sent by php in the modal box to show the appropriate error message.

I would appreciate any help.