$arr = [

    'a' => 'A',

    'b' => 'B',

    'c' => [

        'd'=> 'D',

        'e'=>[

            'f'=>'F',

            'g'=>['h'=>'H']

        ]

    ]

];

//创建一个数组处理函数

function changeCase($var,$type = CASE_UPPER){

    $var = array_change_key_case($var,$type);

      foreach($var as $key => $value){

          if(is_array($value)){

              $var[$key]=changeCase($value);

          }

      }

    return $var;

}

$res = changeCase($arr);

pre($res);

function pre($var){

    echo '<pre>';

    print_r($var);

    echo '</pre>';

}