PHP 替换url中参数

<?php
$url=$_SERVER["argv"][0];
$url1=replace_var($url,"page",100);
echo $url1;
                                                                                                                                               
function replace_var($url,$string,$new_value)
{
        while(substr($url,0,1)=="&")
        {
                $url=substr($url,1);
        }
        if($url!="")
        {
                $url_array=explode("&",$url);
                $new_url=$_SERVER[&#39;PHP_SELF&#39;]."?";
                $string_len=strlen($string)+1;
                $i=0;
                while($url_array[$i])
                {
                         if(substr($url_array[$i],0,$string_len)==$string."=")
                         {
                                $url_array[$i]=$string."=".$new_value;
                        }
                        if($i>0) $url_array[$i]="&".$url_array[$i];
                        $new_url=$new_url.$url_array[$i];
                        $i++;
                }
        }
        else $new_url=$_SERVER[&#39;PHP_SELF&#39;];
        return $new_url;
}
?>