read - read from file
read(fildes, buffer, nbytes)
A file descriptor is a word returned from a successful open, creat, dup,
is the location of nbytes
bytes into which the input will be placed. It is not guaranteed that all
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
file descriptor not that of an input file.
(read = 3.)
(file descriptor in r0)
sys read; buffer; nbytes
(byte count in r0)