v7 man page for read

READ(2) 							System Calls Manual							   READ(2)

NAME
       read - read from file

SYNOPSIS
       read(fildes, buffer, nbytes)
       char *buffer;

DESCRIPTION
       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  type-
       writer 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.

SEE ALSO
       open(2), creat(2), dup(2), pipe(2)

DIAGNOSTICS
       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.

ASSEMBLER
       (read = 3.)
       (file descriptor in r0)
       sys read; buffer; nbytes
       (byte count in r0)

																	   READ(2)