When should I use require vs. include?
The require() function is identical to include(), except that it handles errors differently. If an error occurs, the include() function generates a warning, but the script will continue execution. The require() generates a fatal error, and the script will stop.
When should I use require_once vs. require
The require_once() statement is identical to require() except PHP will check if the file has already been included, and if so, not include (require) it again.
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