This function checks to ensure that the file designated by filename is a valid upload file (meaning that it was uploaded via PHP's HTTP POST upload mechanism). If the file is valid, it will be moved to the filename given by destination.
If filename is not a valid upload file, then no action will occur, and move_uploaded_file() will return FALSE.
If filename is a valid upload file, but cannot be moved for some reason, no action will occur, and move_uploaded_file() will return FALSE. Additionally, a warning will be issued.
This sort of check is especially important if there is any chance that anything done with uploaded files could reveal their contents to the user, or even to other users on the same system.
Замечание: Когда опция safe mode включена, PHP проверяет, имеют ли файлы/каталоги, с которыми вы собираетесь работать, такой же UID, как и выполняемый скрипт.
Замечание: move_uploaded_file() is not affected by the normal safe mode UID-restrictions. This is not unsafe because move_uploaded_file() only operates on files uploaded via PHP.
If the destination file already exists, it will be overwritten.