include(file) include and evaluate the specified file.
The two constructs are identical in every way except how they handle failure:
require(file): a missing file halts processing of the page.
include(file): shows a warning and the script will continue regardless.
include_once(file) are similar to the require() and include() statement,
with the only difference being that if the code from a file has already been included, it will not be included again.