php json_decode解析json文件问题。

怎样能将下面json的格式的value一个一个的用echo显示出来？谢谢

<?php

        $json_file = "list.json";

        $handle = fopen($json_file , "r");

        $contents = fread($handle,filesize($json_file));

        fclose($handle);

//      $js = json_decode($contents);

//      print_r $js;

        foreach (range(4, 3, -1) as $depth) {

                var_dump(json_decode($contents, true, $depth));

        }

?>

输出结果：

array(3) {
["traffic.statistics"]=>
array(2) {
["ethernet.bytes"]=>
int(1901)
["low.protos"]=>
int(2)
}
["detected.protos"]=>
array(2) {
[0]=>
array(4) {
["name"]=>
string(6) "DHCPV6"
["packets"]=>
int(1)
["bytes"]=>
int(149)
["flows"]=>
int(1)
}
[1]=>
array(4) {
["name"]=>
string(5) "LLMNR"
["packets"]=>
int(4)
["bytes"]=>
int(296)
["flows"]=>
int(2)
}
}
["known.flows"]=>
array(0) {
}
}
NULL