使用php为文件提供随机名称

i am trying to give random name to my file name using this code but how do i provide file path and name so it works?

this is my file path

<script type="text/javascript" src="../../js/file.js"></script>

and here's my code

<?php
function random_string($length) {
    $key = '';
    $keys = array_merge(range(0, 9), range('a', 'z'));

    for ($i = 0; $i < $length; $i++) {
        $key .= $keys[array_rand($keys)];
    }

    return $key;
}

echo random_string(50);
?>

this out put wil be like this " i40q6jjmvib6tb36skrutcitok1gxfkprz65e50xsiembjov0b "

and i want it to be like this on my file

<script type="text/javascript" src="../../js/i40q6jjmvib6tb36skrutcitok1gxfkprz65e50xsiembjov0b.js"></script>

<?php
function random_string($length) {
    $key = '';
    $keys = array_merge(range(0, 9), range('a', 'z'));

    for ($i = 0; $i < $length; $i++) {
        $key .= $keys[array_rand($keys)];
    }

    return "js-".$key.".js"; // Change here
}

echo random_string(50);
?>

And in your htaccess, write condition for rewriting /js\-[a-z0-9]*\.js/ to file.js

First rename your file.js file

$random_name = random_string(50);
$dir    = '/your_path/';
$files = scandir($dir, 1);
rename($dir."/".$files[0], $dir."/".$random_name);

And then use this random name in html

<script type="text/javascript" src="../../js/<?php echo $random_name;?>"></script>

Above both code should be in same .php file