What do the dots mean in relative file path?

Question

I am new to programming and learning php on my own. I have two question about the following relative path of a file

$fp = fopen (\"$_SERVER[DOCUMENT_ROOT]/..         


        

Answer 1

.. means "go up one directory".

So, if your DOCUMENT_ROOT was:

/usr/docs/document_root

your path works out to:

/usr/docs/document_root/../orders/orders.txt

Since the .. means "go up one", it in fact becomes:

/usr/docs/orders/orders.txt

You can see how it "erases" the "document_root" part.