What is the difference between include and require in php?

What is the difference between include and require in php?

In PHP, both include and require are used to insert the content of one PHP file into another, but they have a key difference in how they handle errors when the specified file cannot be included.

1. Behavior on File Inclusion Failure:

include: If the file being included does not exist or cannot be found, PHP will emit a warning but will continue executing the script. The rest of the script runs normally.

require: If the file being required does not exist or cannot be found, PHP will emit a fatal error and stop the execution of the script immediately. No further code will be executed.

2. Error Handling:

include: Emits a warning (E_WARNING) and moves on with the script.

require: Emits a fatal error (E_COMPILE_ERROR or E_ERROR), halting the script execution.

Usage Examples:

php

include.php

<?php 
 include 'non_existent_file.php';
  echo "This will still run.";
?>

Output:

A warning is generated, but "This will still run." will be printed.

require.php

<?php 
   require 'non_existent_file.php';
   echo "This will not run.";
?>

Output:

A fatal error is generated, and "This will not run." will never be printed.

3. When to Use:

Use require when the file is essential to the application. For example, if the file contains critical code like database connection or configuration, the script shouldn't continue if it fails to load.

Use include when the file is optional or its absence should not prevent the rest of the script from running.

include_once and require_once:

Both include_once and require_once work similarly to include and require, respectively, but they ensure the file is included only once during script execution, even if called multiple times.