demo.php

<?php

// Usage
include 'UUID.php';

// Pseudo-random UUID
echo UUID::v4();

?>

UUID.php

<?php
/**
 * UUID class
 *
 * The following class generates VALID RFC 4211 COMPLIANT
 * Universally Unique IDentifiers (UUID) version 3, 4 and 5.
 *
 * UUIDs generated validates using OSSP UUID Tool, and output
 * for named-based UUIDs are exactly the same. This is a pure
 * PHP implementation.
 *
 * @author Andrew Moore
 * @link http://www.php.net/manual/en/function.uniqid.php#94959
 */
class UUID {
	/**
	 * 
	 * Generate v4 UUID
	 * 
	 * Version 4 UUIDs are pseudo-random.
	 */
	public static function v4() {
		return sprintf('%04x%04x-%04x-%04x-%04x-%04x%04x%04x',

		// 32 bits for "time_low"
		mt_rand(0, 0xffff), mt_rand(0, 0xffff),

		// 16 bits for "time_mid"
		mt_rand(0, 0xffff),

		// 16 bits for "time_hi_and_version",
		// four most significant bits holds version number 4
		mt_rand(0, 0x0fff) | 0x4000,

		// 16 bits, 8 bits for "clk_seq_hi_res",
		// 8 bits for "clk_seq_low",
		// two most significant bits holds zero and one for variant DCE1.1
		mt_rand(0, 0x3fff) | 0x8000,

		// 48 bits for "node"
		mt_rand(0, 0xffff), mt_rand(0, 0xffff), mt_rand(0, 0xffff)
		);
	}

	public static function is_valid($uuid) {
		return preg_match('/^\{?[0-9a-f]{8}\-?[0-9a-f]{4}\-?[0-9a-f]{4}\-?'.
                      '[0-9a-f]{4}\-?[0-9a-f]{12}\}?$/i', $uuid) === 1;
	}
}
?>