require_once
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(PHP 4, PHP 5, PHP 7, PHP 8)
The require_once expression is identical to require except PHP will check if the file has already been included, and if so, not include (require) it again.
The require_once expression is identical to require() except PHP will check if the file has already been included, and if so, not include (require) it again.
See the include_once() documentation for information about the _once behaviour, and how it differs from its non _once siblings.