Bunget “unreads” the last character read from the current file or data area. This allows the character to be read again by bgetc. This function may be used only for a buffered file or the data area and may be used only once before the next read.
Doread inputs n characters to s from file descriptor fd. Because read(2) does not guarantee that all n characters will be read, doread calls read repeatedly until the buffer is filled, the end of the file is reached or an I/O error occurs. This function supports higher level input functions.
These functions support other input functions and do not directly implement any BASIC functions.
from The Basmark QuickBASIC Programmer’s Manual by Lawrence Leinweber