Разбор, изменение параметров URL string

parseStringUrl.php

<?php
$url = 'http://example.com/search?keyword=test&category=1&tags[]=fun&tags[]=great';

$url_parts = parse_url($url);
parse_str($url_parts['query'], $params);

$params['category'] = 2;     // Overwrite if exists
$params['tags'][] = 'cool';  // Allows multiple values

// Note that this will url_encode all values
$url_parts['query'] = http_build_query($params);

// If you have pecl_http
echo http_build_url($url_parts);

// If not
echo $url_parts['scheme'] . '://' . $url_parts['host'] . $url_parts['path'] . '?' . $url_parts['query'];