Hellohelper.php

<?php
// module/User/src/User/View/Helper/Hellohelper.php

/**
 * Created by PhpStorm.
 * User: mockie
 * Date: 11/8/14
 * Time: 5:33 AM
 */

namespace User\View\Helper;


use Zend\View\Helper\AbstractHelper;

class Hellohelper extends AbstractHelper
{
    public function __invoke($str)
    {
        return $str.' okeee';
    }
}

layout.phtml

            <?php echo $this->hello_helper($this->myvar); ?>

module.cofig.php

//yourModule/config/module.config.php
    'view_helpers' => array(
        'invokables'=> array(
            'hello_helper' => 'User\View\Helper\Hellohelper'
        )
    ),

your_controller.php

public function testAction()
    {
        $this->layout()->myvar = 'teeeeeeeeeeeeest';
}