stream_copy_to_stream()

int stream_copy_to_stream ( resource source, resource dest [, int maxlength [, int offset]] )

Makes a copy of up to maxlength bytes of data from the current position (or from the offset position, if specified) in source to dest. If maxlength is not specified, all remaining content in source will be copied.

stream_copy_to_stream($source_file, $destination_file);