1 .\" Copyright (c) 1980, 1991, 1993
2 .\" The Regents of the University of California. All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
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 .\" 4. 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.
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
28 .\" @(#)dup.2 8.1 (Berkeley) 6/4/93
37 .Nd duplicate an existing file descriptor
45 .Fn dup2 "int oldd" "int newd"
50 duplicates an existing object descriptor and returns its value to
57 is a small non-negative integer index in
58 the per-process descriptor table.
59 The value must be less
60 than the size of the table, which is returned by
62 The new descriptor returned by the call
63 is the lowest numbered descriptor
64 currently not in use by the process.
66 The object referenced by the descriptor does not distinguish
76 are duplicate references to an open
82 calls all move a single pointer into the file,
83 and append mode, non-blocking I/O and asynchronous I/O options
84 are shared between the references.
85 If a separate pointer into the file is desired, a different
86 object reference to the file must be obtained by issuing an
90 The close-on-exec flag on the new file descriptor is unset.
94 the value of the new descriptor
97 If this descriptor is already in use and
101 the descriptor is first deallocated as if the
103 system call had been used.
106 is not a valid descriptor, then
115 is a valid descriptor, then
117 is successful, and does nothing.
121 system call allows file descriptors to be duplicated with restrictions on
124 The value -1 is returned if an error occurs in either call.
125 The external variable
127 indicates the cause of the error.
131 system call fails if:
137 is not a valid active descriptor
139 Too many descriptors are active.
144 system call fails if:
149 argument is not a valid active descriptor or the
151 argument is negative or exceeds the maximum allowable descriptor number
158 .Xr getdtablesize 2 ,
168 system calls are expected to conform to
175 functions appeared in