require vs include in php code example

Example 1: include and require in php

// Include a file, if it can't be found: continue.
<?php
include 'mainfile.php';
?>
  
// Alternatively: Require a file to be imported or quit if it can't be found
<?php
 require 'requiredfile.php';
?>

Example 2: php require vs require_once

//The require statement has two variations, require and require_once.
//The require/require_once statement is used to include file.

// Require a file to be imported or quit if it can't be found
<?php
 require 'requiredfile.php';
?>
// Require_once is ignored if the required file has already been added by any of the include statements.
<?php
 require_once 'require_oncefile.php';
?>

Example 3: require in php

// Require a file to be imported or quit if it can't be found
<?php
 require 'requiredfile.php';
?>