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]/../orders/orders.txt", 'w');

My questions about the relative path in the code above are that:

1. What I understand, $_SERVER[DOCUMENT_ROOT] points to the very root directory of the file structure like htdocs, www or public_html on different servers. Please guide if I am understanding it correctly?
2. What do the two dots mean in the path above?

Thank You

Answer 1

.. means the parent directory, so it goes one level up there and into a sibling directory of your document root called orders.

Answer 2

.. 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.

Answer 3

.. refers to the parent folder.

SO, if $_SERVER[DOCUMENT_ROOT] happens to be /var/www/, the following would be equivalent:

"$_SERVER[DOCUMENT_ROOT]/../orders/orders.txt"
"/var/orders.txt"

Answer 4

I like to think that the two dots drop you down by one directory level, which usually refers to the parent folder. Imagine $_SERVER[DOCUMENT_ROOT] is root:

root/
  index.php   // You are here

orders/
  orders.txt  // You are reading this file

Answer 5

A relative path refers to a location that is relative to a current directory. Relative paths make use of two special symbols, a dot (.) and a double-dot (..), which translate into the current directory and the parent directory. Double dots are used for moving up in the hierarchy.