read - read from a file descriptor


     #include <unistd.h>

     ssize_t read(int fd, void *buf, size_t count


     read() attempts to read up to count bytes from file descrip-
     tor fd into the buffer starting at buf.

     If count is zero, read()  returns  zero  and  has  no  other
     results.   If count is greater than SSIZE_MAX, the result is


     On success, the number of bytes read is returned (zero indi-
     cates  end  of  file),  and the file position is advanced by
     this number.  It is not an error if this number  is  smaller
     than  the  number  of  bytes  requested; this may happen for
     example because fewer bytes are actually available right now
     (maybe  because  we were close to end-of-file, or because we
     are reading from a pipe, or from  a  terminal),  or  because
     read()  was  interrupted  by  a  signal.   On  error,  -1 is
     returned, and errno is set appropriately. In this case it is
     left unspecified whether the file position (if any) changes.


     EINTR   The call was interrupted by a signal before any data
             was read.

     EAGAIN  Non-blocking I/O has been selected using  O_NONBLOCK
             and no data was immediately available for reading.

     EIO     I/O error. This will happen  for  example  when  the
             process  is  in a background process group, tries to
             read from its controlling  tty,  and  either  it  is
             ignoring or blocking SIGTTIN or its process group is
             orphaned.  It may also occur when there  is  a  low-
             level I/O error while reading from a disk or tape.

     EISDIR  fd refers to a directory.

     EBADF   fd is not a valid file descriptor or is not open for

     EINVAL  fd is attached to an object which is unsuitable  for

     EFAULT  buf is outside your accessible address space.

     Other errors may occur, depending on the object connected to
     fd.   POSIX  allows a read that is interrupted after reading
     some data to return -1 (with  errno  set  to  EINTR)  or  to
     return the number of bytes already read.


     SVr4, SVID, AT&T, POSIX, X/OPEN, BSD 4.3


     On NFS file systems, reading small amounts of data will only
     update  the  time stamp the first time, subsequent calls may
     not do so.  This is caused by client side attribute caching,
     because  most  if not all NFS clients leave atime updates to
     the server and client side reads satisfied from the client's
     cache  will  not  cause atime updates on the server as there
     are no server side reads.  UNIX semantics can be obtained by
     disabling  client side attribute caching, but in most situa-
     tions this  will  substantially  increase  server  load  and
     decrease performance.


     readdir(2),   write(2),   write(2),   lseek(2),   select(2),
     readlink(2), ioctl(2),