include / require

[poe]

question,

what is the difference between:

include
require
require once

[Philip]

The include() function produces a Warning while require()  results in a Fatal Error. In other words, use require() if you want a missing file to halt processing of the page. include() does not behave this way, the script will continue regardless. The require_once() statement includes and evaluates the specified file during the execution of the script. This is a behavior similar to the require() statement, with the only difference being that if the code from a file has already been included, it will not be included again.
--Taken from the PHP manual