.\"
.\" Copyright (c) 1993, Sun Microsystems, Inc. All Rights Reserved.
.\" Copyright 1989 AT&T
.\" Copyright 2021 Oxide Computer Company
.\"
.\" The contents of this file are subject to the terms of the
.\" Common Development and Distribution License (the "License").
.\" You may not use this file except in compliance with the License.
.\"
.\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
.\" or http://www.opensolaris.org/os/licensing.
.\" See the License for the specific language governing permissions
.\" and limitations under the License.
.\"
.\" When distributing Covered Code, include this CDDL HEADER in each
.\" file and include the License file at usr/src/OPENSOLARIS.LICENSE.
.\" If applicable, add the following below this CDDL HEADER, with the
.\" fields enclosed by brackets "[]" replaced with your own identifying
.\" information: Portions Copyright [yyyy] [name of copyright owner]
.\"
.Dd July 3, 1990
.Dt FD 4FS
.Os
.Sh NAME
.Nm fd ,
.Nm stdin ,
.Nm stdout ,
.Nm stderr
.Nd file descriptor files
.Sh DESCRIPTION
These files, conventionally called
.Pa /dev/fd/0 ,
.Pa /dev/fd/1 ,
.Pa /dev/fd/2 ,
and so on, refer to files accessible through file descriptors.
If file descriptor
.Em n
is open, these two system calls have the same
effect:
.Bd -literal -offset indent
fd = open("/dev/fd/<n>", mode);
fd = dup(n);
.Ed
.Pp
On these files
.Xr creat 2
is equivalent to
.Xr open 2 ,
and
.Fa mode
is
ignored.
As with
.Xr dup 2 ,
subsequent reads or writes on
.Em fd
fail unless the original file descriptor allows the operations.
.Pp
For convenience in referring to standard input, standard output, and standard
error, an additional set of names is provided:
.Pa /dev/stdin
is a synonym
for
.Pa /dev/fd/0 ,
.Pa /dev/stdout
for
.Pa /dev/fd/1 ,
and
.Pa /dev/stderr
for
.Pa /dev/fd/2 .
.Sh DIAGNOSTICS
.Xr open 2
returns
.Sy -1
and
.Va errno
is set to
.Er EBADF
if the associated file descriptor is not open.
.Sh SEE ALSO
.Xr creat 2 ,
.Xr dup 2 ,
.Xr open 2