Manipulate a url string by adding GET parameters

Question

I want to add GET parameters to URLs that may and may not contain GET parameters without repeating ? or &.

Example:

If I want to add category=action

$url="http://www.acme.com";
 // will add ?category=action at the end

$url="http://www.acme.com/movies?sort=popular";
 // will add &category=action at the end

If you notice I'm trying to not repeat the question mark if it's found.

The URL is just a string.

What is a reliable way to append a specific GET parameter?

Answer 1

Example with updating existent parameters.

Also url_encode used, and possibility to don't specify parameter value

    <?
    /**
     * Add parameter to URL
     * @param string $url
     * @param string $key
     * @param string $value
     * @return string result URL
     */
    function addToUrl($url, $key, $value = null) {
        $query = parse_url($url, PHP_URL_QUERY);
        if ($query) {
            parse_str($query, $queryParams);
            $queryParams[$key] = $value;
            $url = str_replace("?$query", '?' . http_build_query($queryParams), $url);
        } else {
            $url .= '?' . urlencode($key) . '=' . urlencode($value);
        }
        return $url;
    }

Answer 2

another improved function version. Mix of existing answers with small improvements (port support) and bugfixes (checking keys properly).

/**
 * @param string $url original url to modify - can be relative, partial etc
 * @param array $paramsOverride associative array, can be empty
 * @return string modified url
 */
protected function overrideUrlQueryParams($url, $paramsOverride){
    if (!is_array($paramsOverride)){
        return $url;
    }

    $url_parts = parse_url($url);

    if (isset($url_parts['query'])) {
        parse_str($url_parts['query'], $params);
    } else {
        $params = [];
    }

    $params = array_merge($params, $paramsOverride);

    $res = '';

    if(isset($url_parts['scheme'])) {
        $res .= $url_parts['scheme'] . ':';
    }

    if(isset($url_parts['host'])) {
        $res .= '//' . $url_parts['host'];
    }

    if(isset($url_parts['port'])) {
        $res .= ':' . $url_parts['port'];
    }

    if (isset($url_parts['path'])) {
        $res .= $url_parts['path'];
    }

    if (count($params) > 0) {
        $res .= '?' . http_build_query($params);
    }

    return $res;
}