php paths that work on both local (mac) and remote server - php

Question

I'm testing a website on my local machine and I'm wondering what would be the best way to write paths to make sure they work when I upload the site to its final location.
In general I'm a bit confused about paths, and in many cases I have to 'tweak' each path until it works, so wouldn't want to be forced to do the same on a production site!
I'm not clear when to use $_SERVER['DOCUMENT_ROOT'].
For example, I have a directory that I want to scan, which is just under the root. So why can't I just use "/dirname"?
$dir = $_SERVER['DOCUMENT_ROOT'] . '/uploads'; //this works
// $dir = "/uploads"; //this doesn't work
if (is_dir($dir)) {
//do something..
}

Answer 1

I'm not clear when to use
$_SERVER['DOCUMENT_ROOT']. For
example, I have a directory that I
want to scan, which is just under the
root. So why can't I just use
"/dirname"?
When you work with paths in the php file the root (/) is the root of the filesystem, not the root you get when you visit your website.
So $dir = "/uploads"; gives you the filesystem root.
To minify your problems I would declare a variable in a configuration file that specifies the root of your php application, and use that path+whatever more is needed.

Answer 2

As adamse mentioned, the reason you can't use the '/path' is because it points to the root of the filesystem.
However, instead of declaring a variable that defines the root, I recommend using dirname(__FILE__) to retrieve the full path to the directory that the calling file is in.
From there, append relative path information to the file you want and you end up with a complete path, fully dynamically.
For example, if you want to include the 'header.php' file in the directory above the file that you wish to include it in use:
include(dirname(__FILE__) . '/../header.php');
The beauty of that is that PHP will always automatically convert the forward slash to the directory separator required for the host OS.

Answer 3

I would define a variable/constant that describes the absolute filesystem path to the application. Something like this:
$appDir = rtrim(str_replace('\\', '/', realpath(dirname(__FILE__))), '/');
Then you have this base path you can address your application’s files from:
include $appDir.'/library/foo/bar.php';
Or you even change your include path to that directory:
set_include_path($appDir);