php заменить/удалить $_GET параметр в URL

function sgp($url,$varname,$value){
	if(is_array($varname)){
		foreach($varname as $i=>$n){
			$v=(is_array($value))?(isset($value[$i])?$value[$i]:NULL):$value;
			$url=sgp($url,$n,$v);
		}
		return $url;
	}
	preg_match('/^([^?]+)(\?.*?)?(#.*)?$/',$url,$matches);
	$gp=(isset($matches[2]))?$matches[2]:'';
	if(!$gp)return $url;
	$pattern="/([?&])$varname=.*?(?=&|#|\z)/";
	if(preg_match($pattern,$gp)){
		$substitution=($value!=='')?"\${1}$varname=".preg_quote($value):'';
		$newgp=preg_replace($pattern,$substitution,$gp);
		$newgp=preg_replace('/^&/','?',$newgp);
	}
	else{
		$s=($gp)?'&':'?';
		$newgp=$gp.$s.$varname.'='.$value;
	}
	$anchor=(isset($matches[3]))?$matches[3]:'';
	$newurl=$matches[1].$newgp.$anchor;
	$newurl=rtrim($newurl,'&');
	$newurl=str_replace('&&','&',$newurl);
	$newurl=str_replace('?&','?',$newurl);
	return $newurl;
}

<a href="<?=sgp($url,'key',$value)?>">test</a>

<a href="<?=sgp($url,'key','')?>">test</a>

<a href="<?=sgp($url,array('key1','key2'),array($value1,$value2))?>">test</a>

<a href="<?=sgp($url,array('key1','key2'),NULL)?>">test</a>