Include vs Require in PHP: Key Differences and Usage Guide

In PHP, include and require both insert code from one file into another, but require causes a fatal error and stops the script if the file is missing, while include only gives a warning and continues running. Use require when the file is essential, and include when the file is optional.

Quick Comparison

This table summarizes the main differences between include and require in PHP.

Factor	include	require
Error on missing file	Warning (non-fatal)	Fatal error (stops script)
Script continuation after error	Yes, continues	No, stops immediately
Use case	Optional files	Essential files
Behavior on multiple includes	Includes every time	Includes every time
Common usage	Templates, optional configs	Core libraries, critical configs

Key Differences

The main difference between include and require lies in how PHP handles errors when the specified file is missing or unreadable. include generates a warning but allows the script to continue running, which means your program can still execute other code even if the included file is not found.

On the other hand, require triggers a fatal error if the file cannot be loaded, immediately stopping the script. This behavior ensures that critical files, such as configuration or essential functions, must be present for the program to run.

Both statements insert the content of the specified file at the point where they are called, but choosing between them depends on whether the file is optional or mandatory for your application.

Include Example

This example shows how include works when including a file that exists and what happens if the file is missing.

php

<?php
// file: greeting.php
function greet() {
    echo "Hello from included file!\n";
}

// main.php
include 'greeting.php';
greet();

include 'missing.php';
echo "This line still runs despite missing file.\n";
?>

Output

Hello from included file!
Warning: include(missing.php): failed to open stream: No such file or directory in main.php on line 9
Warning: include(): Failed opening 'missing.php' for inclusion (include_path='.:/usr/share/php') in main.php on line 9
This line still runs despite missing file.

Require Equivalent

This example shows how require behaves with the same files. Notice the script stops on missing file.

php

<?php
// file: greeting.php
function greet() {
    echo "Hello from required file!\n";
}

// main.php
require 'greeting.php';
greet();

require 'missing.php';
echo "This line will NOT run because require stops script.\n";
?>

Output

Hello from required file!
Fatal error: require(): Failed opening required 'missing.php' (include_path='.:/usr/share/php') in main.php on line 9

When to Use Which

Choose require when the file is essential for your program to run, such as configuration files, database connections, or core functions. This ensures your script stops immediately if something critical is missing, preventing unexpected behavior.

Use include when the file is optional, like templates, optional features, or user content. This way, your script can continue running even if the file is not found, allowing graceful degradation.

Key Takeaways

Use require for files your script cannot run without.

Use include for optional files where script continuation is allowed.

require stops the script on failure; include only warns and continues.

Both insert file content at the point they are called.

Choosing correctly helps avoid runtime errors and improves code reliability.