lib/getusershell.c

   1 /* getusershell.c -- Return names of valid user shells.
   2    Copyright (C) 1991, 1997 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 /* File containing a list of nonrestricted shells, one per line. */
  26 # define SHELLS_FILE "/etc/shells"
  27 #endif
  28
  29 #include <stdio.h>
  30 #include <ctype.h>
  31
  32 #if defined (STDC_HEADERS) || (!defined (isascii) && !defined (HAVE_ISASCII))
  33 # define IN_CTYPE_DOMAIN(c) 1
  34 #else
  35 # define IN_CTYPE_DOMAIN(c) isascii(c)
  36 #endif
  37
  38 #define ISSPACE(c) (IN_CTYPE_DOMAIN (c) && isspace (c))
  39
  40 #ifdef STDC_HEADERS
  41 # include <stdlib.h>
  42 #else
  43 char *malloc ();
  44 char *realloc ();
  45 #endif
  46
  47 char *xstrdup ();
  48
  49 static int readname ();
  50
  51 /* List of shells to use if the shells file is missing. */
  52 static char const* const default_shells[] =
  53 {
  54   "/bin/sh", "/bin/csh", "/usr/bin/sh", "/usr/bin/csh", NULL
  55 };
  56
  57 /* Index of the next shell in `default_shells' to return.
  58    0 means we are not using `default_shells'. */
  59 static int default_index = 0;
  60
  61 /* Input stream from the shells file. */
  62 static FILE *shellstream = NULL;
  63
  64 /* Line of input from the shells file. */
  65 static char *line = NULL;
  66
  67 /* Number of bytes allocated for `line'. */
  68 static int line_size = 0;
  69 \f
  70 /* Return an entry from the shells file, ignoring comment lines.
  71    If the file doesn't exist, use the list in DEFAULT_SHELLS (above).
  72    In any case, the returned string is in memory allocated through malloc.
  73    Return NULL if there are no more entries.  */
  74
  75 char *
  76 getusershell ()
  77 {
  78   if (default_index > 0)
  79     {
  80       if (default_shells[default_index])
  81         /* Not at the end of the list yet.  */
  82         return xstrdup (default_shells[default_index++]);
  83       return NULL;
  84     }
  85
  86   if (shellstream == NULL)
  87     {
  88       shellstream = fopen (SHELLS_FILE, "r");
  89       if (shellstream == NULL)
  90         {
  91           /* No shells file.  Use the default list.  */
  92           default_index = 1;
  93           return xstrdup (default_shells[0]);
  94         }
  95     }
  96
  97   while (readname (&line, &line_size, shellstream))
  98     {
  99       if (*line != '#')
 100         return line;
 101     }
 102   return NULL;                  /* End of file. */
 103 }
 104
 105 /* Rewind the shells file. */
 106
 107 void
 108 setusershell ()
 109 {
 110   default_index = 0;
 111   if (shellstream == NULL)
 112     shellstream = fopen (SHELLS_FILE, "r");
 113   else
 114     fseek (shellstream, 0L, 0);
 115 }
 116
 117 /* Close the shells file. */
 118
 119 void
 120 endusershell ()
 121 {
 122   if (shellstream)
 123     {
 124       fclose (shellstream);
 125       shellstream = NULL;
 126     }
 127 }
 128
 129 /* Allocate N bytes of memory dynamically, with error checking.  */
 130
 131 static char *
 132 xmalloc (n)
 133      unsigned n;
 134 {
 135   char *p;
 136
 137   p = malloc (n);
 138   if (p == 0)
 139     {
 140       fprintf (stderr, "virtual memory exhausted\n");
 141       exit (1);
 142     }
 143   return p;
 144 }
 145
 146 /* Reallocate space P to size N, with error checking.  */
 147
 148 static char *
 149 xrealloc (p, n)
 150      char *p;
 151      unsigned n;
 152 {
 153   p = realloc (p, n);
 154   if (p == 0)
 155     {
 156       fprintf (stderr, "virtual memory exhausted\n");
 157       exit (1);
 158     }
 159   return p;
 160 }
 161
 162 /* Read a line from STREAM, removing any newline at the end.
 163    Place the result in *NAME, which is malloc'd
 164    and/or realloc'd as necessary and can start out NULL,
 165    and whose size is passed and returned in *SIZE.
 166
 167    Return the number of characters placed in *NAME
 168    if some nonempty sequence was found, otherwise 0.  */
 169
 170 static int
 171 readname (name, size, stream)
 172      char **name;
 173      int *size;
 174      FILE *stream;
 175 {
 176   int c;
 177   int name_index = 0;
 178
 179   if (*name == NULL)
 180     {
 181       *size = 10;
 182       *name = (char *) xmalloc (*size);
 183     }
 184
 185   /* Skip blank space.  */
 186   while ((c = getc (stream)) != EOF && ISSPACE (c))
 187     /* Do nothing. */ ;
 188
 189   while (c != EOF && !ISSPACE (c))
 190     {
 191       (*name)[name_index++] = c;
 192       while (name_index >= *size)
 193         {
 194           *size *= 2;
 195           *name = (char *) xrealloc (*name, *size);
 196         }
 197       c = getc (stream);
 198     }
 199   (*name)[name_index] = '\0';
 200   return name_index;
 201 }
 202
 203 #ifdef TEST
 204 main ()
 205 {
 206   char *s;
 207
 208   while (s = getusershell ())
 209     puts (s);
 210   exit (0);
 211 }
 212 #endif