Question

Short version:
How do relative paths work in php?

Long version:
I have a local web site (http://test.com) and E:\test\ is its document root. This is my Directory tree:

1. E:\test\001.php
2. E:\test\exit.php
3. E:\test\death.txt
4. E:\test\mysql\first.php
5. E:\test\mysql\death.txt
6. E:\test\mysql\exit.php

And Contents of files:

E:\test\001.php

<?php

include('mysql/first.php');

?>

E:\test\exit.php

<?php
die('What?');
?>

E:\test\death.txt

Bonjour

E:\test\mysql\first.php

<?php
echo file_get_contents('death.txt');
include('exit.php');
?>

E:\test\mysql\death.txt

Hello there

E:\test\mysql\exit.php

<?php
die('DONE');
?>

If I browse http://test.com/001.php and E:\test\exit.php and E:\test\death.txt exist, I get this:

BonjourWhat?

And If they don’t exist:

Warning: file_get_contents(death.txt) [function.file-get-contents]: failed to open stream: No such file or directory in E:\test\mysql\first.php on line 2
DONE

How do relative paths workin php? I thought it should give me warning for both files or show proper output !

I’m testing this code on Win7 x64 with XAMPP, php 5.3.

Answer 1

This is how the documentation on php.net describes the PHP include search mechanism:

1. First, it will look in the include_path:
   http://php.net/manual/en/ini.core.php#ini.include-path.
2. Then it will try to load the file in the calling script’s own directory if it could not find anything in the include_path. (in our
   case, the root directory)
3. Finally, if everything else failed, it will then try to find the file in the current directory.

When I ran your scripts, my include path was set to .: by default (the current directory and nothing else), so when I try to load death.txt and exit.php from mysql/first.php it should search in ./ folder which is the current directory. But… It does not. The current directory should be mysql/ but it’s not pointing there… So what’s happening here?

PHP is quite special with that… Let’s rollback to the first statement we made. What is PHP interpreting in our include path when it uses the . is actually a path resolution again! So, looking at our path, we have . which can’t be interpreted (./. again?) to anything using our include_path. Then, PHP has to go to the second path resolution (2) which is the root directory of our script. (have you got an headache yet? Because I do)

Using get_include_path() and realpath() you can observe this:

Included path: '.:'
Including mysql/first.php: /Users/Kouno/Development/SandBox/test-php/mysql/first.php
This is what `realpath` returns for './': /Users/Kouno/Development/SandBox/test-php
Getting content of death.txt: /Users/Kouno/Development/SandBox/test-php/death.txt
Bonjour
Including exit.php: /Users/Kouno/Development/SandBox/test-php/exit.php
What?

Then, why does it specifically fail to load mysql/death.txt but still find mysql/exit.php, once you remove death.txt and exit.php from your root directory? It should find both of them, right?

Well, it’s because get_file_content has a second parameter which ignores include_path by default.

If you set the second parameter:

echo file_get_contents('death.txt', FILE_USE_INCLUDE_PATH);

Then you would get the expected result.

Included path: '.:'
Including mysql/first.php: /Users/Kouno/Development/SandBox/test-php/mysql/first.php
Getting content of death.txt: (no path returned)
Hello there
Including exit.php: (no path returned)
DONE

The funny thing is that get_file_content() will start using the same mechanism as include (and this is not documented properly on php.net). And realpath() doesn’t even implement this mechanism at all (which explains why I have a no path returned showing up).

Hope this helps!