How to get the relative path of a file in PHP, _PHP tutorial

<&#63;php
$a = '/a/b/c/d/e.php';
$b = '/a/b/12/34/c.php';
//../../12/34/c.php
echo getRelativelyPath($a,$b);
//求$b相对于$a的相对路径
function getRelativelyPath($a,$b){ 
$a=explode('/',$a);
$b=explode('/',$b);
var_dump($a);
//print_r($b);
$c=array_values(array_diff($a,$b));
$d=array_values(array_diff($b,$a));
// var_dump($c);
//var_dump($d);
array_pop($c);
foreach($c as &$v){
$v='..';
}
var_dump($c);
var_dump($d);
$arr=array_merge($c,$d);
var_dump($arr);
$str=implode("/",$arr);
echo $str;
}