1.\" Copyright (c) 2013 Jilles Tjoelker 2.\" 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.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.\" $FreeBSD: head/lib/libc/gen/dup3.3 254488 2013-08-18 13:25:18Z jilles $ 26.\" 27.Dd August 16, 2013 28.Dt DUP3 3 29.Os 30.Sh NAME 31.Nm dup3 32.Nd duplicate an existing file descriptor 33.Sh LIBRARY 34.Lb libc 35.Sh SYNOPSIS 36.In fcntl.h 37.In unistd.h 38.Ft int 39.Fn dup3 "int oldd" "int newd" "int flags" 40.Sh DESCRIPTION 41The 42.Fn dup3 43function 44duplicates an existing object descriptor 45while allowing the value of the new descriptor to be specified. 46.Pp 47The close-on-exec flag on the new file descriptor is determined by the 48.Dv O_CLOEXEC 49bit in 50.Fa flags . 51.Pp 52If 53.Fa oldd 54\*(Ne 55.Fa newd 56and 57.Fa flags 58== 0, 59the behavior is identical to 60.Li dup2(oldd, newd) . 61.Pp 62If 63.Fa oldd 64== 65.Fa newd , 66then 67.Fn dup3 68fails, unlike 69.Xr dup2 2 . 70.Sh RETURN VALUES 71The value -1 is returned if an error occurs. 72The external variable 73.Va errno 74indicates the cause of the error. 75.Sh ERRORS 76The 77.Fn dup3 78function fails if: 79.Bl -tag -width Er 80.It Bq Er EBADF 81The 82.Fa oldd 83argument is not a valid active descriptor or the 84.Fa newd 85argument is negative or exceeds the maximum allowable descriptor number 86.It Bq Er EINVAL 87The 88.Fa oldd 89argument is equal to the 90.Fa newd 91argument. 92.It Bq Er EINVAL 93The 94.Fa flags 95argument has bits set other than 96.Dv O_CLOEXEC . 97.El 98.Sh SEE ALSO 99.Xr accept 2 , 100.Xr close 2 , 101.Xr dup2 2 , 102.Xr fcntl 2 , 103.Xr getdtablesize 2 , 104.Xr open 2 , 105.Xr pipe 2 , 106.Xr socket 2 , 107.Xr socketpair 2 108.Sh STANDARDS 109The 110.Fn dup3 111function does not conform to any standard. 112.Sh HISTORY 113The 114.Fn dup3 115function appeared in 116.Fx 10.0 117and 118.Dx 5.5 . 119