PHP Including Files And Securing Included Files Tutorial

This is a short tutorial that show how to include PHP files and how to secure these. For example: when including a file that runs a process that may only be used internally, you don't want the file to be accessible directly. However this is easy to secure against, we'll see that later in this tutorial. Let's start with the multiple ways to include a PHP file:

include

include("filename.php");

The PHP include function is the easiest way to include a PHP file into your PHP webpage. All it does is include the file given as argument to the function, no matter if it's already include before. If it fails to include the file, it will return a warning ( but won't stop the script from functioning further ).

include_once

include_once("filename.php");

The PHP include_once function is a little different from the normal include function. This function ( the name says it all ) includes a file only ONCE. If the specified file has already been included earlier in the script, it will not include it again.

require

require("filename.php");

The PHP require function is another way to include a PHP file into your webpage. The difference with the include function is that the script will not function further ( it wil throw a fatal error ) when the specified file could not be included.

require_once

require_once("filename.php");

The PHP require_once function can include the specified file ( or: its code ) only once. For the rest it works the same as the normal require function.