Digits.php

<?php
/**
 * Zend Framework (http://framework.zend.com/)
 *
 * @link      http://github.com/zendframework/zf2 for the canonical source repository
 * @copyright Copyright (c) 2005-2012 Zend Technologies USA Inc. (http://www.zend.com)
 * @license   http://framework.zend.com/license/new-bsd New BSD License
 * @package   Zend_Filter
 */

namespace Zend\Filter;

/**
 * @category   Zend
 * @package    Zend_Filter
 */
class Digits extends AbstractFilter
{
    /**
     * Defined by Zend\Filter\FilterInterface
     *
     * Returns the string $value, removing all but digit characters
     *
     * @param  string $value
     * @return string
     */
    public function filter($value)
    {
        if (!static::hasPcreUnicodeSupport()) {
            // POSIX named classes are not supported, use alternative 0-9 match
            $pattern = '/[^0-9]/';
        } elseif (extension_loaded('mbstring')) {
            // Filter for the value with mbstring
            $pattern = '/[^[:digit:]]/';
        } else {
            // Filter for the value without mbstring
            $pattern = '/[\p{^N}]/';
        }

        return preg_replace($pattern, '', (string) $value);
    }
}