Relative and Absolute Paths in PHP - Enhanced Guide

1. Intro
2. Difference between Absolute and Relative Paths
3. Absolute Paths
4. Relative Paths
5. Document Root
6. Web Server Paths
7. Console Scripts
8. Helpful PHP Commands and Constants

Intro

Websites exist in two worlds: the real (filesystem) and the virtual (web). Understanding this distinction is critical for PHP developers.

For example, in http://example.com/file.html, the browser does not see a physical file—it only requests a virtual resource. Whether a file exists on disk is irrelevant to the browser.

Developers, however, work with the real files on disk. PHP scripts interact with these files when including scripts, reading data, or writing logs.

Difference between Absolute and Relative Paths

Paths can be classified as:

• Absolute: Start from the root of the filesystem or site.
• Relative: Start from the current working directory or location.

Analogy: A postal address "123 Main St" is absolute, while "Turn right two blocks" is relative.

Absolute Paths

Absolute paths always start from the root:

• Unix: /var/www/site/index.php
• Windows: C:\Windows\system32\cmd.exe

Absolute paths are reliable: no matter where you start, the path points to the same file.

Relative Paths

Relative paths depend on the current working directory:

• index.html — same folder
• ./file.php — current folder
• images/pic.jpg — subfolder
• ../file.php — parent folder

// Current folder: /var/www/site/about
include '../config/settings.php'; 
// Resolves to /var/www/site/config/settings.php

Document Root

The DOCUMENT_ROOT is the filesystem folder that corresponds to the site root. Example:

/var/www/site/forum/index.php
http://example.com/forum/index.php

For PHP to access this file:

$file = $_SERVER['DOCUMENT_ROOT'] . '/forum/index.php';

Web Server Paths

For the browser, paths start from the site root:

• Absolute URL: /job/vacancy.php
• Relative URL: vacancy.php from /about/ folder resolves incorrectly

Console Scripts (Single Entry Point)

In CLI scripts, $_SERVER['DOCUMENT_ROOT'] is unavailable. Use __DIR__ to build paths:

$configPath = __DIR__ . '/../config/settings.php';
require $configPath;

define('ROOT_DIR', realpath(__DIR__ . '/../'));
include ROOT_DIR . '/config/settings.php';

Helpful PHP Commands and Constants

• __FILE__ — full path to the current file
• __DIR__ — current folder
• realpath() — converts relative path to absolute
• getcwd() — current working directory