1/* Copyright (C) 1991-2022 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, see
16 <https://www.gnu.org/licenses/>. */
17
18#include <errno.h>
19#include <fcntl.h>
20#include <limits.h>
21#include <unistd.h>
22
23/* Duplicate FD to FD2, closing the old FD2 and making FD2 be
24 open the same file as FD is. Return FD2 or -1. */
25int
26__dup2 (int fd, int fd2)
27{
28 int save;
29
30 if (fd2 < 0
31#ifdef OPEN_MAX
32 || fd2 >= OPEN_MAX
33#endif
34)
35 {
36 __set_errno (EBADF);
37 return -1;
38 }
39
40 /* Check if FD is kosher. */
41 if (fcntl (fd, F_GETFL) < 0)
42 return -1;
43
44 if (fd == fd2)
45 return fd2;
46
47 /* This is not atomic. */
48
49 save = errno;
50 (void) close (fd2);
51 __set_errno (save);
52
53 return fcntl (fd, F_DUPFD, fd2);
54}
55libc_hidden_def (__dup2)
56weak_alias (__dup2, dup2)
57

source code of glibc/sysdeps/posix/dup2.c