What are the differences between require and include, include_once?
The include_once() function includes and evaluates the specified file during the execution of the php script. It's behavior is similar to the include() function but the only difference is that if the code from a file has already been included, it will not be included again.
include();--> include the file, but in case of file missing throws a warning and continues execution of code of next line.
require();--> require also includes the file but in case of file missing throws an fatal error and stop the execution of the code of next line.
include_once();-->if same file was included first it will not include the file another time.