.\" Copyright (c) 1990 The Regents of the University of California.
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.\" developed by the University of California, Berkeley and its contributors''
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.\"	@(#)fd.4	5.1 (Berkeley) 5/10/90
.\"
.TH FD 4 "May 10, 1990"
.UC 7
.SH NAME
fd, stdin, stdout, stderr \- file descriptor files
.SH DESCRIPTION
The files
.I /dev/fd/0
through
.I /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:
.sp
.RS
fd = open("/dev/fd/0", mode);
.RE
.sp
and the call:
.sp
.RS
fd = fcntl(0, F_DUPFD, 0);
.RE
.sp
are equivalent.
.PP
Opening the files
.IR /dev/stdin ,
.I /dev/stdout
and
.I /dev/stderr
is equivalent to the following calls:
.sp
.RS
fd = fcntl(STDIN_FILENO,  F_DUPFD, 0);
.br
fd = fcntl(STDOUT_FILENO, F_DUPFD, 0);
.br
fd = fcntl(STDERR_FILENO, F_DUPFD, 0);
.RE
.PP
Flags to the
.IR open (2)
call other than O_RDONLY, O_WRONLY and O_RDWR are ignored.
.SH FILES
/dev/fd/#
.br
/dev/stdin
.br
/dev/stdout
.br
/dev/stderr
.SH SEE ALSO
tty(4)