How does include path resolution work in require_once?

Question

I was writing an web app in PHP, when I encountered a strange situation. To illustrate my problem, consider a web app of this structure:

/
    index.php
    f1/
        f1.php
    f2/
        f2.php

Contents of these files:

index.php:

<?php require_once("f1/f1.php"); ?>

f1.php:

<?php require_once("../f2/f2.php"); ?>

f2.php: blank

now when I try to open index.php in my browser I get this error:

Warning: require_once(../f2/f2.php) [function.require-once]: 
failed to open stream: No such file or directory in /var/www/reqtest/f1/f1.php on line 2
Fatal error: require_once() [function.require]: 
Failed opening required '../f2/f2.php' (include_path='.:/usr/share/php:/usr/share/pear') in /var/www/reqtest/f1/f1.php on line 2

Is there something obvious I'm missing? how do include paths work in PHP?

---

Before I asked this question, I attempted to experiment and find out. I set up another test, like so:

/
    index.php
    f1/
        f1.php
        f2.php

index.php:

<?php require_once("f1/f1.php"); ?>

f1.php:

<?php require_once("f2.php"); ?>

f2.php: blank

To my surprise (and utter confusion), this worked out fine!

So, what is the secret behind the path resolution?

PS I saw this question, but it still does not answer the second case that I've stated here.

Answer 1

If you include another file, the working directory remains where the including file is.

Your examples are working as intended.

Edit: The second example works because . (actual directory) is in your include path (see your error message).

Edit2: In your second example, the key point of your interest is this line:

<?php require_once("f2.php"); ?>

At first it will look in the current working dir (/var/www/req_path_test), but does not find f2.php.

As fallback, it will try to find f2.php in your include_path ('.:/usr/share/php:/usr/share/pear'), starting with '.' (which is relative to the actual file, not the including one).

So './f2.php' works and the require does not fail.

Answer 2

When you open index.php, working dir is set to the folder this file resides in. And inside insluded f1.php this working dir does not change.

You can include files by using their absolute paths, relative to the current included file like this:

require_once(dirname(__FILE__).'/../../test/file.php')

But better consider using an autoloader if these files contain classes.

Answer 3

Normaly in you old structure

<?php require_once("f2/f2.php"); ?>

instead of

<?php require_once("../f2/f2.php"); ?>

should work. As far as i know php takes the paths from the initial script

Answer 4

It sounds like your server has the open_basedir setting enabled in the PHP configuration. This makes it impossible to include (and open) files in folders above your in the directory structur (i.e., you can't use ../ to go up in the folder structure).

Answer 5

From the PHP Docs PHP include

Files are included based on the file path given or, if none is given, the include_path specified. If the file isn't found in the include_path, include will finally check in the calling script's own directory and the current working directory before failing.

If the file path is not given then i.e require_once("f2.php");

1st. The include_path is checked

2nd. The calling scripts own directory is checked

3rd. Finally the current working directory is checked

If file not found then PHP throws warning on file include & fatal error on require

If a path is defined — whether absolute (starting with a drive letter or \ on Windows, or / on Unix/Linux systems) or relative to the current directory (starting with . or ..) — the include_path will be ignored altogether. For example, if a filename begins with ../, the parser will look in the parent directory to find the requested file.

If you include/require your file beginning with . or .. or ./ then PHP's parser will look in the parent directory which is the current working directory i.e require_once("../f2/f2.php"), php will check at the root directory as the calling script index.php is in that directory.

Now You have not defined any include path in your PHP script thus it always falls back to the calling script and then into the current working directory.

// Check your default include path, most likely to be C:\xampp\php\PEAR
echo get_include_path();

// To set include path
set_include_path ( string $new_include_path ) : string

The Current Working Directory is derived from your main calling script index.php.

// The Current Working Directory can be checked
echo getcwd();

In the first Example where the required file "../f2/f2.php" is from f1.php

You code does not work because -

1. The specified path is ignored by PHP as your filename begins with ../
2. f1/ the calling script's own directory is ignored as well.
3. The parser directory looks into the parent directory to find the requested file. The current working directory is root directory, this is from where you have initiated the working script index.php. The file is not located at this directory, wrong path given.

Thus you get the Fatal Error

In the Second example you have changed the directory & from f1.php you require_once("f2.php").

Your code works because -

1. This time you require("f2.php") no leading ../ or ./ This time PHP checks the include_path but does find it there, as you haven't defined it and the file does not reside in the default preset include_path.
2. This time the calling script f1.php's directory is f1/. and you require file ("f2.php") is located at this directory. PHP This time checks the file in this directory and finds it.
3. PHP does not have to check the working directory as the file was found.

Thus Your Code Works Fine!