1.\" Copyright (c) 1990, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)fd.4 8.1 (Berkeley) 6/9/93 29.\" $FreeBSD$ 30.\" 31.Dd June 9, 1993 32.Dt FD 4 33.Os 34.Sh NAME 35.Nm fd , 36.Nm stdin , 37.Nm stdout , 38.Nm stderr 39.Nd file descriptor files 40.Sh DESCRIPTION 41The files 42.Pa /dev/fd/0 43through 44.Pa /dev/fd/# 45refer to file descriptors which can be accessed through the file 46system. 47If the file descriptor is open and the mode the file is being opened 48with is a subset of the mode of the existing descriptor, the call: 49.Bd -literal -offset indent 50fd = open("/dev/fd/0", mode); 51.Ed 52.Pp 53and the call: 54.Bd -literal -offset indent 55fd = fcntl(0, F_DUPFD, 0); 56.Ed 57.Pp 58are equivalent. 59.Pp 60Opening the files 61.Pa /dev/stdin , 62.Pa /dev/stdout 63and 64.Pa /dev/stderr 65is equivalent to the following calls: 66.Bd -literal -offset indent 67fd = fcntl(STDIN_FILENO, F_DUPFD, 0); 68fd = fcntl(STDOUT_FILENO, F_DUPFD, 0); 69fd = fcntl(STDERR_FILENO, F_DUPFD, 0); 70.Ed 71.Pp 72Flags to the 73.Xr open 2 74call other than 75.Dv O_RDONLY , 76.Dv O_WRONLY 77and 78.Dv O_RDWR 79are ignored. 80.Sh IMPLEMENTATION NOTES 81By default, 82.Pa /dev/fd 83is provided by 84.Xr devfs 5 , 85which provides nodes for the first three file descriptors. 86Some sites may require nodes for additional file descriptors; these can be 87made available by mounting 88.Xr fdescfs 5 89on 90.Pa /dev/fd . 91.Sh FILES 92.Bl -tag -width /dev/stderr -compact 93.It Pa /dev/fd/# 94.It Pa /dev/stdin 95.It Pa /dev/stdout 96.It Pa /dev/stderr 97.El 98.Sh SEE ALSO 99.Xr tty 4 , 100.Xr devfs 5 , 101.Xr fdescfs 5 102