read - read input
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).