Difference between require,include,require_once and include_once?

When you use require  vs. include ?

The require() function is identical to include(), except that it handles errors differently. If an error occurs, the include() function generates a warning, but the script will continue execution. The require() generates a fatal error, and the script will stop.

When you use require_once vs. require ?

The require_once() statement is identical to require() except PHP will check if the file has already been included, and if so, not include (require) it again.

PHP Include & PHP Include_once

The “include” php statement is used to include other files into a PHP file.

It has two variations, include and include_once.  Include_once is ignored by the PHP interpreter if the file to be included.

The include statement has the following syntax

<?php                        
include 'file_name';    
?> 

The include_once statement has the following syntax

<?php                              
include_once 'file_name';
?>                                                         

HERE,

“Include/include_once” is the statement that includes file

“'file_name'” is the name of the file to be included.

PHP Require & PHP require_once

The require statement has two variations, require and require_once.

The require/require_once statement is used to include file.

Require_once is ignored if the required file has already been added by any of the four include statements.

It has the following syntax
require 'file_name';                   
? >                                            
<?php                                       
require_once 'file_name';         

?>                  
    

The “include” and “require” statements can be used at any line in the source codes where you want the code to appear.