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.Dd August 16, 2013 26.Dt DUP3 3 27.Os 28.Sh NAME 29.Nm dup3 30.Nd duplicate an existing file descriptor 31.Sh LIBRARY 32.Lb libc 33.Sh SYNOPSIS 34.In fcntl.h 35.In unistd.h 36.Ft int 37.Fn dup3 "int oldd" "int newd" "int flags" 38.Sh DESCRIPTION 39The 40.Fn dup3 41function 42duplicates an existing object descriptor 43while allowing the value of the new descriptor to be specified. 44.Pp 45The close-on-exec flag on the new file descriptor is determined by the 46.Dv O_CLOEXEC 47bit in 48.Fa flags . 49.Pp 50If 51.Fa oldd 52\*(Ne 53.Fa newd 54and 55.Fa flags 56== 0, 57the behavior is identical to 58.Li dup2(oldd, newd) . 59.Pp 60If 61.Fa oldd 62== 63.Fa newd , 64then 65.Fn dup3 66fails, unlike 67.Xr dup2 2 . 68.Sh RETURN VALUES 69The value -1 is returned if an error occurs. 70The external variable 71.Va errno 72indicates the cause of the error. 73.Sh ERRORS 74The 75.Fn dup3 76function fails if: 77.Bl -tag -width Er 78.It Bq Er EBADF 79The 80.Fa oldd 81argument is not a valid active descriptor or the 82.Fa newd 83argument is negative or exceeds the maximum allowable descriptor number 84.It Bq Er EINVAL 85The 86.Fa oldd 87argument is equal to the 88.Fa newd 89argument. 90.It Bq Er EINVAL 91The 92.Fa flags 93argument has bits set other than 94.Dv O_CLOEXEC . 95.El 96.Sh SEE ALSO 97.Xr accept 2 , 98.Xr close 2 , 99.Xr dup2 2 , 100.Xr fcntl 2 , 101.Xr getdtablesize 2 , 102.Xr open 2 , 103.Xr pipe 2 , 104.Xr socket 2 , 105.Xr socketpair 2 106.Sh STANDARDS 107The 108.Fn dup3 109function does not conform to any standard. 110.Sh HISTORY 111The 112.Fn dup3 113function appeared in 114.Fx 10.0 . 115