What is common difference between include, require and require once?

Question

difference - include and require

Answer 1

include = If fail to import the script throw an error but continue running.
require= If fail to import the script throw an error and block the remaining part of the script.
Add "_once" is to make sure that the script is only import once, if for some reason you need to import X time the same script you use require or include but if you want to make sure that your code will only keep 1 import running you add the suffix.