FD(4) BSD Kernel Interfaces Manual FD(4)NAME
fd, stdin, stdout, stderr — file descriptor files
DESCRIPTION
The files /dev/fd/0 through /dev/fd/# refer to file descriptors 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 addi‐
tional file descriptors; these can be made available by mounting
fdescfs(5) on /dev/fd.
FILES
/dev/fd/#
/dev/stdin
/dev/stdout
/dev/stderr
SEE ALSOtty(4), devfs(5), fdescfs(5)BSD June 9, 1993 BSD
