MkDir Failed creating directory PHP - php

Question

I am trying to create a directory using PHP this works:
<?php
$uid = "user_615";
$thisdir = getcwd();
if(mkdir($thisdir ."/userpics/" . $uid , 0777))
{
echo "Directory has been created successfully...";
}
else
{
echo "Failed to create directory...";
}
?>
but this does not work
<?php
session_start();
$uid = $_SESSION['username'];
$thisdir = getcwd();
if(mkdir($thisdir ."/userpics/" . $uid , 0777))
{
echo "Directory has been created successfully...";
}
else
{
echo "Failed to create directory...";
}
?>
Yes the session variable is populated with the exact same thing as above 'user_615' so why would the second one be failing?
EDIT:
So I took the suggestion of #stefgosselin and re-designed the code to be
<?php
session_start();
$uid = $_SESSION['username'];
$thisdir = getcwd() . "/userpics" . $uid;
if(mkdir($thisdir , 0777))
{
echo "Directory has been created successfully...";
}
else
{
echo "Failed to create directory...";
echo "Your thisdir Variable is:'" . $thisdir . "'" ;
}
?>
And the output is
Failed to create directory...Your thisdir Variable is:'/unified/b/bis/www.mysite.com/jou/userpics/user_615
Any other ideas on what would cause the a Session variable not to be able to used in creating a directory?

Answer 1

As a small tip, I would simply put all of $thisdir in a variable and check if the output of that adds up to the result you are expecting.
IE: Having $thisdir ."/userpics/" . $uid defined in a variable would give you the possibility to easily output and validate the argument value you are passing to mkdir.
Edit: Adjusted minor phrasing for better english translation. Sorry above wasn't clear, Wesley understood the simple point I was clumsily trying to make.