read - read from a file descriptor
ssize_t read(int fd, void *buf, size_t count);
read() attempts to read up to count bytes from file descriptor 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 unspecified.
On success, the number of bytes read is returned (zero indicates 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 pro-
cess 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 reading.
EINVAL fd is attached to an object which is unsuitable for reading.
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
SVr4, SVID, AT&T, POSIX, X/OPEN, BSD 4.3
Many filesystems and disks were considered to be fast enough that the
implementation of O_NONBLOCK was deemed unneccesary. So, O_NONBLOCK may
not be available on files and/or disks.
close(2), fcntl(2), ioctl(2), lseek(2), readdir(2), readlink(2),
select(2), write(2), fread(3), readv(3)
Linux 2.0.32 1997-07-12 read(2)