read(fildes, buffer, nbytes)
A file descriptor is a word returned from a successful open, creat, dup,
or pipe call. Buffer is the location of nbytes contiguous
bytes into which the input will be placed. It is not guaranteed that all
nbytes bytes will be read; for example if the file refers to a
typewriter at most one line will be returned. In any event the number of
characters read is returned.
If the returned value is 0, then end-of-file has been reached.
open(2), creat(2), dup(2), pipe(2)
As mentioned, 0 is returned when the end of the file has been reached. If the
read was otherwise unsuccessful the return value is -1. Many conditions can
generate an error: physical I/O errors, bad buffer address, preposterous
nbytes, file descriptor not that of an input file.
(read = 3.)
(file descriptor in r0)
sys read; buffer; nbytes
(byte count in r0)