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.\" 30.Dd June 9, 1993 31.Dt FD 4 32.Os 33.Sh NAME 34.Nm fd , 35.Nm stdin , 36.Nm stdout , 37.Nm stderr 38.Nd file descriptor files 39.Sh DESCRIPTION 40The files 41.Pa /dev/fd/0 42through 43.Pa /dev/fd/# 44refer to file descriptors which can be accessed through the file 45system. 46If the file descriptor is open and the mode the file is being opened 47with is a subset of the mode of the existing descriptor, the call: 48.Bd -literal -offset indent 49fd = open("/dev/fd/0", mode); 50.Ed 51.Pp 52and the call: 53.Bd -literal -offset indent 54fd = fcntl(0, F_DUPFD, 0); 55.Ed 56.Pp 57are equivalent. 58.Pp 59Opening the files 60.Pa /dev/stdin , 61.Pa /dev/stdout 62and 63.Pa /dev/stderr 64is equivalent to the following calls: 65.Bd -literal -offset indent 66fd = fcntl(STDIN_FILENO, F_DUPFD, 0); 67fd = fcntl(STDOUT_FILENO, F_DUPFD, 0); 68fd = fcntl(STDERR_FILENO, F_DUPFD, 0); 69.Ed 70.Pp 71Flags to the 72.Xr open 2 73call other than 74.Dv O_RDONLY , 75.Dv O_WRONLY 76and 77.Dv O_RDWR 78are ignored. 79.Sh IMPLEMENTATION NOTES 80By default, 81.Pa /dev/fd 82is provided by 83.Xr devfs 5 , 84which provides nodes for the first three file descriptors. 85Some sites may require nodes for additional file descriptors; these can be 86made available by mounting 87.Xr fdescfs 5 88on 89.Pa /dev/fd . 90.Sh FILES 91.Bl -tag -width /dev/stderr -compact 92.It Pa /dev/fd/# 93.It Pa /dev/stdin 94.It Pa /dev/stdout 95.It Pa /dev/stderr 96.El 97.Sh SEE ALSO 98.Xr tty 4 , 99.Xr devfs 5 , 100.Xr fdescfs 5 101