Allows you to easily modify an existing URL's query string parameters, overriding or simply adding new (while preserving existing parameters, if desired).

updateQueryString.php

<?php

/**
 * Allows you to easily modify an existing URL's query string parameters, overriding or simply adding new (while
 * preserving existing parameters, if desired).
 *
 * @param	string	$url		URL you wish to update.
 * @param	array	$params		Array of key/value combos. Set value to null to REMOVE the parameter.
 * @param	bool	$override	Indicates if this should override parameters or not.
 * @return	string
 */
function updateQueryString($url, $params = [], $override = true) {
	// Get existing parameters from the provided URL.
	$urlParts = explode("?", $url);
	$origParams = [];
	if (!empty($urlParts[1])) parse_str($urlParts[1], $origParams);

	// Setup new parameters (depending on override setting).
	if ($override) {
		$params = array_merge($origParams, $params);
	} else {
		$params = array_merge($params, $origParams);
	}

	// Remove any null parameters (but allow other falsey values, e.g. 0).
	$params = array_filter($params, function($val) {return $val !== null;});

	// Rebuild query string and setup with URL.
	$url = $urlParts[0];
	if (count($params) > 0) $url .= "?" . http_build_query($params);
	return $url;
}