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. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)fd.4 8.1 (Berkeley) 6/9/93 33.\" $FreeBSD$ 34.\" 35.Dd June 9, 1993 36.Dt FD 4 37.Os 38.Sh NAME 39.Nm fd , 40.Nm stdin , 41.Nm stdout , 42.Nm stderr 43.Nd file descriptor files 44.Sh DESCRIPTION 45The files 46.Pa /dev/fd/0 47through 48.Pa /dev/fd/# 49refer to file descriptors which can be accessed through the file 50system. 51If the file descriptor is open and the mode the file is being opened 52with is a subset of the mode of the existing descriptor, the call: 53.Bd -literal -offset indent 54fd = open("/dev/fd/0", mode); 55.Ed 56.Pp 57and the call: 58.Bd -literal -offset indent 59fd = fcntl(0, F_DUPFD, 0); 60.Ed 61.Pp 62are equivalent. 63.Pp 64Opening the files 65.Pa /dev/stdin , 66.Pa /dev/stdout 67and 68.Pa /dev/stderr 69is equivalent to the following calls: 70.Bd -literal -offset indent 71fd = fcntl(STDIN_FILENO, F_DUPFD, 0); 72fd = fcntl(STDOUT_FILENO, F_DUPFD, 0); 73fd = fcntl(STDERR_FILENO, F_DUPFD, 0); 74.Ed 75.Pp 76Flags to the 77.Xr open 2 78call other than 79.Dv O_RDONLY , 80.Dv O_WRONLY 81and 82.Dv O_RDWR 83are ignored. 84.Sh IMPLEMENTATION NOTES 85By default, 86.Pa /dev/fd 87is provided by 88.Xr devfs 5 , 89which provides nodes for the first three file descriptors. 90Some sites may require nodes for additional file descriptors; these can be 91made available by mounting 92.Xr fdescfs 5 93on 94.Pa /dev/fd . 95.Sh FILES 96.Bl -tag -width /dev/stderr -compact 97.It Pa /dev/fd/# 98.It Pa /dev/stdin 99.It Pa /dev/stdout 100.It Pa /dev/stderr 101.El 102.Sh SEE ALSO 103.Xr tty 4 , 104.Xr devfs 5 , 105.Xr fdescfs 5 106