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NAME
read - read from a file descriptor
SYNOPSIS
ssize_t read(int fd, void *buf, size_t count);
DESCRIPTION
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.
RETURN VALUE
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 hap-
pen 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.
ERRORS
EINTR The call was interrupted by a signal before any
data was read.
EAGAIN Non-blocking I/O has been selected using O_NON-
BLOCK 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 reading.
EINVAL fd is attached to an object which is unsuitable
for reading.
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.
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