算出两个文件的相对路径

$a = '/a/b/c/d/e/g/f.php';
$b = '/a/b/12/34/c.php';

$arr_a=explode('/',$a);$arr_b=explode('/',$b);
$count_a=count($arr_a);$count_b=count($arr_b);
for($i=0;$i<($count_a-1);$i++)
{
if($arr_a["$i"] != $arr_b["$i"])
{
$haha.='/'.$arr_a["$i"];
echo "<br>";
$dian[]=$count_b-$i-1;
}
}
$haha = substr($haha,1);
for($j=0;$j<$dian['0'];$j++)
{
$yao='../';
$re .= $yao;
}
echo $re.$haha;