READ(2)

NAME
read - read from a file descriptor

SYNOPSIS
#include <unistd.h>

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. If count is greater than SSIZE_MAX, the result is unspecified.

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 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.

ERRORS

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.

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.

CONFORMING TO
SVID, AT&T, POSIX, X/OPEN, BSD 4.3

SEE ALSO
readdir(2), write(2), write(2), fcntl(2), close(2), lseek(2), select(2), readlink(2), ioctl(2), fread(3).