What is the difference between require() and require_once()?

require() and require_once() both are used for include PHP files into another PHP files. But the difference is with the help of require() we can include the same file many times in a single page, but in case of require_once() we can call the same file many times, but PHP includes that file only single time.

Note: From the vast number of php basic interview questions, answering this will help you to align yourself as an expert in the subject. This is a very tricky question that often makes developers nervous.