fd(4)

NAME

fd, stdin, stdout, stderr - file descriptor files

DESCRIPTION

The files /dev/fd/0 through /dev/fd/# refer to file descrip

tors which can
be accessed through the file system. If the file descriptor

is open and
the mode the file is being opened with is a subset of the

mode of the
existing descriptor, the call:

fd = open("/dev/fd/0", mode);

and the call:

fd = fcntl(0, F_DUPFD, 0);

are equivalent.

Opening the files /dev/stdin, /dev/stdout and /dev/stderr is

equivalent
to the following calls:

fd = fcntl(STDIN_FILENO, F_DUPFD, 0);
fd = fcntl(STDOUT_FILENO, F_DUPFD, 0);
fd = fcntl(STDERR_FILENO, F_DUPFD, 0);

Flags to the open(2) call other than O_RDONLY, O_WRONLY and

O_RDWR are
ignored.

IMPLEMENTATION NOTES

By default, /dev/fd is provided by devfs(5), which provides

nodes for the
first three file descriptors. Some sites may require nodes

for additional file descriptors; these can be made available by

mounting
fdescfs(5) on /dev/fd.

FILES

/dev/fd/#
/dev/stdin
/dev/stdout
/dev/stderr

SEE ALSO

tty(4), devfs(5), fdescfs(5)

BSD June 9, 1993

BSD