lib/getusershell.c

   1 /* getusershell.c -- Return names of valid user shells.
   2    Copyright (C) 1991, 1997, 2000, 2001 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 David MacKenzie <djm@gnu.ai.mit.edu> */
  19
  20 #ifdef HAVE_CONFIG_H
  21 # include <config.h>
  22 #endif
  23
  24 #ifndef SHELLS_FILE
  25 # ifndef __DJGPP__
  26 /* File containing a list of nonrestricted shells, one per line. */
  27 #  define SHELLS_FILE "/etc/shells"
  28 # else
  29 /* This is a horrible kludge.  Isn't there a better way?  */
  30 #  define SHELLS_FILE "/dev/env/DJDIR/etc/shells"
  31 # endif
  32 #endif
  33
  34 #include <stdio.h>
  35 #if HAVE_STDLIB_H
  36 # include <stdlib.h>
  37 #endif
  38 #include <ctype.h>
  39 #include "unlocked-io.h"
  40 #include "xalloc.h"
  41
  42 #if defined (STDC_HEADERS) || (!defined (isascii) && !defined (HAVE_ISASCII))
  43 # define IN_CTYPE_DOMAIN(c) 1
  44 #else
  45 # define IN_CTYPE_DOMAIN(c) isascii(c)
  46 #endif
  47
  48 #define ISSPACE(c) (IN_CTYPE_DOMAIN (c) && isspace (c))
  49
  50 static int readname ();
  51
  52 #if ! defined ADDITIONAL_DEFAULT_SHELLS && defined __MSDOS__
  53 # define ADDITIONAL_DEFAULT_SHELLS \
  54   "c:/dos/command.com", "c:/windows/command.com", "c:/command.com",
  55 #else
  56 # define ADDITIONAL_DEFAULT_SHELLS /* empty */
  57 #endif
  58
  59 /* List of shells to use if the shells file is missing. */
  60 static char const* const default_shells[] =
  61 {
  62   ADDITIONAL_DEFAULT_SHELLS
  63   "/bin/sh", "/bin/csh", "/usr/bin/sh", "/usr/bin/csh", NULL
  64 };
  65
  66 /* Index of the next shell in `default_shells' to return.
  67    0 means we are not using `default_shells'. */
  68 static int default_index = 0;
  69
  70 /* Input stream from the shells file. */
  71 static FILE *shellstream = NULL;
  72
  73 /* Line of input from the shells file. */
  74 static char *line = NULL;
  75
  76 /* Number of bytes allocated for `line'. */
  77 static int line_size = 0;
  78 \f
  79 /* Return an entry from the shells file, ignoring comment lines.
  80    If the file doesn't exist, use the list in DEFAULT_SHELLS (above).
  81    In any case, the returned string is in memory allocated through malloc.
  82    Return NULL if there are no more entries.  */
  83
  84 char *
  85 getusershell ()
  86 {
  87   if (default_index > 0)
  88     {
  89       if (default_shells[default_index])
  90         /* Not at the end of the list yet.  */
  91         return xstrdup (default_shells[default_index++]);
  92       return NULL;
  93     }
  94
  95   if (shellstream == NULL)
  96     {
  97       shellstream = fopen (SHELLS_FILE, "r");
  98       if (shellstream == NULL)
  99         {
 100           /* No shells file.  Use the default list.  */
 101           default_index = 1;
 102           return xstrdup (default_shells[0]);
 103         }
 104     }
 105
 106   while (readname (&line, &line_size, shellstream))
 107     {
 108       if (*line != '#')
 109         return line;
 110     }
 111   return NULL;                  /* End of file. */
 112 }
 113
 114 /* Rewind the shells file. */
 115
 116 void
 117 setusershell ()
 118 {
 119   default_index = 0;
 120   if (shellstream)
 121     rewind (shellstream);
 122 }
 123
 124 /* Close the shells file. */
 125
 126 void
 127 endusershell ()
 128 {
 129   if (shellstream)
 130     {
 131       fclose (shellstream);
 132       shellstream = NULL;
 133     }
 134 }
 135
 136 /* Read a line from STREAM, removing any newline at the end.
 137    Place the result in *NAME, which is malloc'd
 138    and/or realloc'd as necessary and can start out NULL,
 139    and whose size is passed and returned in *SIZE.
 140
 141    Return the number of characters placed in *NAME
 142    if some nonempty sequence was found, otherwise 0.  */
 143
 144 static int
 145 readname (name, size, stream)
 146      char **name;
 147      int *size;
 148      FILE *stream;
 149 {
 150   int c;
 151   int name_index = 0;
 152
 153   if (*name == NULL)
 154     {
 155       *size = 10;
 156       *name = (char *) xmalloc (*size);
 157     }
 158
 159   /* Skip blank space.  */
 160   while ((c = getc (stream)) != EOF && ISSPACE (c))
 161     /* Do nothing. */ ;
 162
 163   while (c != EOF && !ISSPACE (c))
 164     {
 165       (*name)[name_index++] = c;
 166       while (name_index >= *size)
 167         {
 168           *size *= 2;
 169           *name = (char *) xrealloc (*name, *size);
 170         }
 171       c = getc (stream);
 172     }
 173   (*name)[name_index] = '\0';
 174   return name_index;
 175 }
 176
 177 #ifdef TEST
 178 main ()
 179 {
 180   char *s;
 181
 182   while (s = getusershell ())
 183     puts (s);
 184   exit (0);
 185 }
 186 #endif