1.\" $NetBSD: fd.4,v 1.6 2013/12/30 08:42:00 dholland Exp $ 2.\" 3.\" Copyright (c) 1990, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)fd.4 8.1 (Berkeley) 6/9/93 31.\" 32.Dd December 29, 2013 33.Dt FD 4 34.Os 35.Sh NAME 36.Nm fd , 37.Nm stdin , 38.Nm stdout , 39.Nm stderr 40.Nd file descriptor files 41.Sh DESCRIPTION 42The files 43.Pa /dev/fd/0 44through 45.Pa /dev/fd/# 46refer to file descriptors which can be accessed through the file 47system. 48If the file descriptor is open and the mode the file is being opened 49with is a subset of the mode of the existing descriptor, the call: 50.Bd -literal -offset indent 51fd = open("/dev/fd/0", mode); 52.Ed 53.Pp 54and the call: 55.Bd -literal -offset indent 56fd = fcntl(0, F_DUPFD, 0); 57.Ed 58.Pp 59are equivalent. 60.Pp 61Opening the files 62.Pa /dev/stdin , 63.Pa /dev/stdout 64and 65.Pa /dev/stderr 66is equivalent to the following calls: 67.Bd -literal -offset indent 68fd = fcntl(STDIN_FILENO, F_DUPFD, 0); 69fd = fcntl(STDOUT_FILENO, F_DUPFD, 0); 70fd = fcntl(STDERR_FILENO, F_DUPFD, 0); 71.Ed 72.Pp 73Flags to the 74.Xr open 2 75call other than 76.Dv O_RDONLY , 77.Dv O_WRONLY 78and 79.Dv O_RDWR 80are ignored. 81.Sh FILES 82.Bl -tag -width /dev/stderr -compact 83.It Pa /dev/fd/# 84.It Pa /dev/stdin 85.It Pa /dev/stdout 86.It Pa /dev/stderr 87.El 88.Sh SEE ALSO 89.Xr tty 4 , 90.Xr mount_fdesc 8 91.Ss NOTE 92The floppy disk driver on some ports is also called 93.Nm fd ; 94see 95.Xr fdc 4 96for its documentation. 97