read - read input

     #include <sys/types.h>
     #include <unistd.h>

     ssize_t read(int d, void *buf, size_t nbytes)

     Read attempts to read nbytes of data from the object  referenced  by  the
     descriptor d into the buffer pointed to by buf.

     On objects capable of seeking, the read starts at a position given by the
     pointer  associated  with  d  (see lseek(2)).  Upon return from read, the
     pointer is incremented by the number of bytes actually read.

     Objects that are not capable of seeking  always  read  from  the  current
     position.   The  value  of  the pointer associated with such an object is

     Upon successful completion, read return the number of bytes actually read
     and  placed  in  the buffer.  The system guarantees to read the number of
     bytes requested if the descriptor references a normal file that has  that
     many bytes left before the end-of-file, but in no other case.

     If the returned value is 0, then end-of-file has been reached.

     If successful, the number of bytes actually read is returned.  Otherwise,
     a  -1  is  returned  and the global variable errno is set to indicate the

     Read will fail if one or more of the following are true:

     [EBADF]        D is not a valid descriptor open for reading.

     [EFAULT]       Buf points outside the allocated address space.

     [EIO]          An I/O error occurred while reading from the file system.

     [EINTR]        A read from a slow device was interrupted before any  data
                    arrived by the delivery of a signal.

     [EAGAIN]       The file was marked for non-blocking I/O, and no data were
                    ready to be read.

     dup(2), fcntl(2), open(2), pipe(2), write(2).