【转】得到两个文件的相对路径 [php]

function compara_path($path_a,$path_b){
$array_a = explode('/',$path_a);
$array_b = explode('/',$path_b);
echo count($array_a);

$file_a = array_pop($array_a);
$file_b = array_pop($array_b);

$a_len = count($array_a);
$b_len = count($array_b);
echo $a_len;

for($i=0;$i<$a_len;$i++){
if($array_a[$i] != $array_b[$i]){
break;
}
}
echo $i;
$com_path = "";
for($j=0;$j<$a_len-$i;$j++){
$com_path .= '../';
}
for($i;$i<$b_len;$i++){
$com_path .= $array_b[$i].'/';
}
$com_path .= $file_b;
echo $com_path;
}
$path_a = "/home/a/b/c/d/d/xxx.txt";
$path_b = "/home/a/b/e/i/h/e/f/xxxxx.txt";
compara_path($path_a, $path_b);