What is the difference between the require and include functions in PHP?

Differences in error handling when including a file.

• require: When an error occurs (file not found or inaccessible), it generates a fatal error (E_COMPILE_ERROR), and script execution stops.
• include: When an error occurs, it generates a warning (E_WARNING), but script execution continues.

Function	Error type on failure	Continue execution
require	E_COMPILE_ERROR	No
include	E_WARNING	Yes

Using require is preferable for critical files (e.g., configuration, libraries), without which the script's work is meaningless. include is suitable for optional files (e.g., templates, widgets).

There are also require_once and include_once versions, which check if the file has already been included and include it only once.

<?php

// Example of using require
// If the file non_existent_critical_file.php does not exist, the script will stop.
// require 'non_existent_critical_file.php';

// Example of using include
// If the file non_existent_optional_file.php does not exist, a warning will be issued,
// but the script will continue.
// include 'non_existent_optional_file.php';

?>