php - Customizable Path for file_get_contents based on Session

one text

I dont know how to solve this issue, I have tried to look for an answer, but all I get is that I should put it between .'filename'.like this file_get_contents('../jsonFIle/' . $_SESSION['nameF'] . '.json');

I am trying to let the user input an existing json file name and it should change the context of the website from that json file. I am also a beginner and any links to how I could solve this would be appreciated

Index.php

<?php
session_start();
$local_dir = 'C:\xampp\htdocs\jsonFile';
$files = checkDir($local_dir);
$_SESSION['nameF'] = $_POST['fname'];
function checkDir($dir)
{
    return array_values(array_diff(scandir($dir) , array(
        '.',
        '..'
    )));
}
//default json file 
if (count($files) == 0 || session_id() !== '')
    {
        $jsonData = file_get_contents('../jsonFIle/Ass2News.json');
        $json = json_decode($jsonData, true);
    }
    //new updated file
    else
    {
        $jsonData = file_get_contents('../jsonFIle/' . $_SESSION['nameF'] . '.json');
        $json = json_decode($jsonData, true);
    }
?>

input.php

<?php
session_start();

include ("connection.php");
include ("functions.php");

$user_data = check_login($con);

if (isset($_POST['submit'])){
    $fname=$_POST['fname'];
}

?>
<!DOCTYPE html>
<html>
<head>
<title>Update News File</title>
</head>
<body>

<form action='../test/index.php' method='post'>
  <label for="fname">File name:</label>
  <input type="text" name="fname"><br><br>
  <input type="submit" id="buttonS"name="apply" value="Apply">
</form>

</body>

</html>

Source