Folder with Random Name and Save file to it with PHP - php

Question

So I am creating trying to create a PHP script where the client can create a folder with a 10 digit name of random letters and numbers, and than save the document they are currently working on into that folder. Its like a JSfiddle where you can save what you are currently working on and it makes a random folder. My issue is that it wont create my directory, and the idea is correct, and it should work. However, PHP isn't saving an Error Log so I cannot identify the issue. Here's what I got so far.
PHP
save_functions.php
<?php
function genRandomString() {
$length = 10;
$characters = "0123456789abcdefghijklmnopqrstuvwxyz";
$string = '';
for ($p = 0; $p < $length; $p++) {
$string .= $characters[mt_rand(0, strlen($characters))];
}
return $string;
}
<?php
function createFolder() {
$folderName = genRandomString(); //Make a random name for the folder
$goTo = '../$folderName';//Path to folder
while(is_dir($goTo)==true){ //Check if a folder with that name exists
$folderName = genRandomString();
$goTo = '../$folderName';
}
mkdir($goTo,7777); //Make a directory with that name at $goTo
return $goTo; //Return the path to the folder
}
?>
create_files.php
<?php
include('save_functions.php');//Include those functions
$doc = $_POST['doc'];//Get contents of the file
$folder = createFolder();//Make the folder with that random name
$docName = '$folder/style.css';//Create the css file
$dh = fopen($docName, 'w+') or die("can't open file");//Open or create the file
fwrite($dh, $doc);//Overwrite contents of the file
fclose($dh);//Close handler
?>

Answer 1

The call to mkdir($goTo,7777) has wrong mode, this is usually octal and not decimal or hex. 7777 is 017141 in octal and thus tries to set non-existent bits. Try the usual 0777.
But why don't you just use tempnam() or tmpfile() in your case?