11/3/71                                             SYS READ (II)

NAME            read  --  read from file

SYNOPSIS        (file descriptor in r0)

                sys     read; buffer; nchars    / read = 3.

                (nread in r0)

DESCRIPTION     A file descriptor is a word returned from a suc-

                cessful open call.

                Buffer is the location of nchars contiguous bytes

                into which the input will be placed.  It is not

                guaranteed that all nchars bytes will be read,

                however; 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 re-

                turned in r0.

                If r0 returns with value 0, then end-of-file has

                been reached.

FILES           --

SEE ALSO        open

DIAGNOSTICS     As mentioned, r0 is 0 on return when the end of

                the file has been reached.  If the read was

                otherwise unsuccessful the error bit (c-bit) is

                set.  Many conditions, all rare, can generate an

                error: physical I/O errors, bad buffer address,

                preposterous nchars, file descriptor not that of

                an input file.

BUGS            --

OWNER           ken, dmr