.\" Copyright (c) 1990, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)fd.4 8.1 (Berkeley) 6/9/93 .\" $FreeBSD: src/share/man/man4/fd.4,v 1.5.2.1 2001/07/21 09:16:46 schweikh Exp $ .\" $DragonFly: src/share/man/man4/fd.4,v 1.2 2003/06/17 04:36:59 dillon Exp $ .\" .Dd June 9, 1993 .Dt FD 4 .Os .Sh NAME .Nm fd , .Nm stdin , .Nm stdout , .Nm stderr .Nd file descriptor files .Sh DESCRIPTION The files .Pa /dev/fd/0 through .Pa /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: .Bd -literal -offset indent fd = open("/dev/fd/0", mode); .Ed .Pp and the call: .Bd -literal -offset indent fd = fcntl(0, F_DUPFD, 0); .Ed .Pp are equivalent. .Pp Opening the files .Pa /dev/stdin , .Pa /dev/stdout and .Pa /dev/stderr is equivalent to the following calls: .Bd -literal -offset indent fd = fcntl(STDIN_FILENO, F_DUPFD, 0); fd = fcntl(STDOUT_FILENO, F_DUPFD, 0); fd = fcntl(STDERR_FILENO, F_DUPFD, 0); .Ed .Pp Flags to the .Xr open 2 call other than .Dv O_RDONLY , .Dv O_WRONLY and .Dv O_RDWR are ignored. .Sh FILES .Bl -tag -width /dev/stderr -compact .It Pa /dev/fd/# .It Pa /dev/stdin .It Pa /dev/stdout .It Pa /dev/stderr .El .Sh SEE ALSO .Xr tty 4