sysdeps/unix/getlogin.c

   1 /* Copyright (C) 1991, 1992, 1996, 1997 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, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <errno.h>
  20 #include <unistd.h>
  21 #include <string.h>
  22 #include <stdio.h>
  23 #include <limits.h>
  24 #include <fcntl.h>
  25
  26 #include <utmp.h>
  27
  28 /* Return the login name of the user, or NULL if it can't be determined.
  29    The returned pointer, if not NULL, is good only until the next call.  */
  30
  31 char *
  32 getlogin (void)
  33 {
  34   char tty_pathname[2 + 2 * NAME_MAX];
  35   char *real_tty_path = tty_pathname;
  36   char *result = NULL;
  37   static char name[UT_NAMESIZE + 1];
  38   struct utmp *ut, line, buffer;
  39
  40   /* Get name of tty connected to fd 0.  Return NULL if not a tty or
  41      if fd 0 isn't open.  Note that a lot of documentation says that
  42      getlogin() is based on the controlling terminal---what they
  43      really mean is "the terminal connected to standard input".  The
  44      getlogin() implementation of DEC Unix, SunOS, Solaris, HP-UX all
  45      return NULL if fd 0 has been closed, so this is the compatible
  46      thing to do.  Note that ttyname(open("/dev/tty")) on those
  47      systems returns /dev/tty, so that is not a possible solution for
  48      getlogin().  */
  49   if (__ttyname_r (0, real_tty_path, sizeof (tty_pathname)) != 0)
  50     return NULL;
  51
  52   real_tty_path += 5;           /* Remove "/dev/".  */
  53
  54   __setutent ();
  55   strncpy (line.ut_line, real_tty_path, sizeof line.ut_line);
  56   if (__getutline_r (&line, &buffer, &ut) < 0)
  57     {
  58       if (errno == ESRCH)
  59         /* The caller expects ENOENT if nothing is found.  */
  60         __set_errno (ENOENT);
  61       result = NULL;
  62     }
  63   else
  64     {
  65       strncpy (name, ut->ut_user, UT_NAMESIZE);
  66       name[UT_NAMESIZE] = '\0';
  67       result = name;
  68     }
  69
  70   __endutent ();
  71
  72   return result;
  73 }