Absolute path & Relative Path

Question

What's the difference between absolute path & relative path when using any web server or Tomcat?

Answer 1

Absolute paths start with / and refer to a location from the root of the current site (or virtual host).

Relative paths do not start with / and refer to a location from the actual location of the document the reference is made.

Examples, assuming root is http://foo.com/site/

Absolute path, no matter where we are on the site

/foo.html

will refer to http://foo.com/site/foo.html

Relative path, assuming the containing link is located in http://foo.com/site/part1/bar.html

../part2/quux.html

will refer to http://foo.com/site/part2/quux.html

or

part2/blue.html

will refer to http://foo.com/site/part1/part2/blue.html

Answer 2

Important to note that relative paths are also subjective.

ie:

<?php 
  #bar.php
  require('../foo.php'); 
?>

/dir/bar.php 
/foo.php         # prints a 
/dir/foo.php # prints b 
/dir/other/   # empty dir

$ pwd 
>  /
$ php dir/bar.php 
>  / + ../foo.php == /foo.php   
>  prints a 
$ cd dir 
$ php bar.php
>  /dir  + ../foo.php = /foo.php 
>  prints a
$ cd other
$ php ../bar.php 
> /dir/other + ../foo.php  = /dir/foo.php 
> prints b

This can create some rather confusing situations, especially if you have many files with releative references and multiple possible places that can act as an "entry point" that controls what the relative path is relative to.

In such situations, one should compute the absolute path manually based on a fixed known, ie:

<?php
    require( realpath(dirname(__FILE__) . '/../foo.php') )

or

<?php
   require( SOMECONSTANT . '/relative/path.php'  ); 

or

<?php
   require( $_SERVER['DOCUMENT_ROOT'] . '/relative/path.php' );