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.Dd June 9, 1993 29.Dt FD 4 30.Os 31.Sh NAME 32.Nm fd , 33.Nm stdin , 34.Nm stdout , 35.Nm stderr 36.Nd file descriptor files 37.Sh DESCRIPTION 38The files 39.Pa /dev/fd/0 40through 41.Pa /dev/fd/# 42refer to file descriptors which can be accessed through the file 43system. 44If the file descriptor is open and the mode the file is being opened 45with is a subset of the mode of the existing descriptor, the call: 46.Bd -literal -offset indent 47fd = open("/dev/fd/0", mode); 48.Ed 49.Pp 50and the call: 51.Bd -literal -offset indent 52fd = fcntl(0, F_DUPFD, 0); 53.Ed 54.Pp 55are equivalent. 56.Pp 57Opening the files 58.Pa /dev/stdin , 59.Pa /dev/stdout 60and 61.Pa /dev/stderr 62is equivalent to the following calls: 63.Bd -literal -offset indent 64fd = fcntl(STDIN_FILENO, F_DUPFD, 0); 65fd = fcntl(STDOUT_FILENO, F_DUPFD, 0); 66fd = fcntl(STDERR_FILENO, F_DUPFD, 0); 67.Ed 68.Pp 69Flags to the 70.Xr open 2 71call other than 72.Dv O_RDONLY , 73.Dv O_WRONLY 74and 75.Dv O_RDWR 76are ignored. 77.Sh IMPLEMENTATION NOTES 78By default, 79.Pa /dev/fd 80is provided by 81.Xr devfs 4 , 82which provides nodes for the first three file descriptors. 83Some sites may require nodes for additional file descriptors; these can be 84made available by mounting 85.Xr fdescfs 4 86on 87.Pa /dev/fd . 88.Sh FILES 89.Bl -tag -width /dev/stderr -compact 90.It Pa /dev/fd/# 91.It Pa /dev/stdin 92.It Pa /dev/stdout 93.It Pa /dev/stderr 94.El 95.Sh SEE ALSO 96.Xr devfs 4 , 97.Xr fdescfs 4 , 98.Xr tty 4 99