lib/dup2.c

   1 /* Duplicate an open file descriptor to a specified file descriptor.
   2    Copyright 1999 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 2, or (at your option)
   7    any later version.
   8
   9    This program 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
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, write to the Free Software Foundation,
  16    Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  17
  18 /* written by Paul Eggert */
  19
  20 #if HAVE_CONFIG_H
  21 # include <config.h>
  22 #endif
  23
  24 #include <errno.h>
  25 #ifndef errno
  26 extern int errno;
  27 #endif
  28
  29 #if HAVE_FCNTL_H
  30 # include <fcntl.h>
  31 #endif
  32
  33 #if HAVE_UNISTD_H
  34 # include <unistd.h>
  35 #endif
  36
  37 #ifndef F_DUPFD
  38 static int
  39 dupfd (int fd, int desired_fd)
  40 {
  41   int duplicated_fd = dup (fd);
  42   if (duplicated_fd < 0 || duplicated_fd == desired_fd)
  43     return duplicated_fd;
  44   else
  45     {
  46       int r = dupfd (fd, desired_fd);
  47       int e = errno;
  48       close (duplicated_fd);
  49       errno = e;
  50       return r;
  51     }
  52 }
  53 #endif
  54
  55 int
  56 dup2 (int fd, int desired_fd)
  57 {
  58   if (fd == desired_fd)
  59     return fd;
  60   close (desired_fd);
  61 #ifdef F_DUPFD
  62   return fcntl (fd, F_DUPFD, desired_fd);
  63 #else
  64   return dupfd (fd, desired_fd);
  65 #endif
  66 }