lib/dup2.c

   1 /* Duplicate an open file descriptor to a specified file descriptor.
   2    Copyright (C) 1999, 2004 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
  26 #if HAVE_FCNTL_H
  27 # include <fcntl.h>
  28 #endif
  29
  30 #if HAVE_UNISTD_H
  31 # include <unistd.h>
  32 #endif
  33
  34 #ifndef F_DUPFD
  35 static int
  36 dupfd (int fd, int desired_fd)
  37 {
  38   int duplicated_fd = dup (fd);
  39   if (duplicated_fd < 0 || duplicated_fd == desired_fd)
  40     return duplicated_fd;
  41   else
  42     {
  43       int r = dupfd (fd, desired_fd);
  44       int e = errno;
  45       close (duplicated_fd);
  46       errno = e;
  47       return r;
  48     }
  49 }
  50 #endif
  51
  52 int
  53 dup2 (int fd, int desired_fd)
  54 {
  55   if (fd == desired_fd)
  56     return fd;
  57   close (desired_fd);
  58 #ifdef F_DUPFD
  59   return fcntl (fd, F_DUPFD, desired_fd);
  60 #else
  61   return dupfd (fd, desired_fd);
  62 #endif
  63 }