lib/getusershell.c

   1 /* getusershell.c -- Return names of valid user shells.
   2    Copyright (C) 1991 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
  16    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, 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 #ifdef STDC_HEADERS
  33 #include <stdlib.h>
  34 #else
  35 char *malloc ();
  36 char *realloc ();
  37 #endif
  38
  39 char *xstrdup ();
  40
  41 static int readname ();
  42
  43 /* List of shells to use if the shells file is missing. */
  44 static char const* const default_shells[] =
  45 {
  46   "/bin/sh", "/bin/csh", "/usr/bin/sh", "/usr/bin/csh", NULL
  47 };
  48
  49 /* Index of the next shell in `default_shells' to return.
  50    0 means we are not using `default_shells'. */
  51 static int default_index = 0;
  52
  53 /* Input stream from the shells file. */
  54 static FILE *shellstream = NULL;
  55
  56 /* Line of input from the shells file. */
  57 static char *line = NULL;
  58
  59 /* Number of bytes allocated for `line'. */
  60 static int line_size = 0;
  61 \f
  62 /* Return an entry from the shells file, ignoring comment lines.
  63    If the file doesn't exist, use the list in DEFAULT_SHELLS (above).
  64    In any case, the returned string is in memory allocated through malloc.
  65    Return NULL if there are no more entries.  */
  66
  67 char *
  68 getusershell ()
  69 {
  70   if (default_index > 0)
  71     {
  72       if (default_shells[default_index])
  73         /* Not at the end of the list yet.  */
  74         return xstrdup (default_shells[default_index++]);
  75       return NULL;
  76     }
  77
  78   if (shellstream == NULL)
  79     {
  80       shellstream = fopen (SHELLS_FILE, "r");
  81       if (shellstream == NULL)
  82         {
  83           /* No shells file.  Use the default list.  */
  84           default_index = 1;
  85           return xstrdup (default_shells[0]);
  86         }
  87     }
  88
  89   while (readname (&line, &line_size, shellstream))
  90     {
  91       if (*line != '#')
  92         return line;
  93     }
  94   return NULL;                  /* End of file. */
  95 }
  96
  97 /* Rewind the shells file. */
  98
  99 void
 100 setusershell ()
 101 {
 102   default_index = 0;
 103   if (shellstream == NULL)
 104     shellstream = fopen (SHELLS_FILE, "r");
 105   else
 106     fseek (shellstream, 0L, 0);
 107 }
 108
 109 /* Close the shells file. */
 110
 111 void
 112 endusershell ()
 113 {
 114   if (shellstream)
 115     {
 116       fclose (shellstream);
 117       shellstream = NULL;
 118     }
 119 }
 120
 121 /* Allocate N bytes of memory dynamically, with error checking.  */
 122
 123 static char *
 124 xmalloc (n)
 125      unsigned n;
 126 {
 127   char *p;
 128
 129   p = malloc (n);
 130   if (p == 0)
 131     {
 132       fprintf (stderr, "virtual memory exhausted\n");
 133       exit (1);
 134     }
 135   return p;
 136 }
 137
 138 /* Reallocate space P to size N, with error checking.  */
 139
 140 static char *
 141 xrealloc (p, n)
 142      char *p;
 143      unsigned n;
 144 {
 145   p = realloc (p, n);
 146   if (p == 0)
 147     {
 148       fprintf (stderr, "virtual memory exhausted\n");
 149       exit (1);
 150     }
 151   return p;
 152 }
 153
 154 /* Read a line from STREAM, removing any newline at the end.
 155    Place the result in *NAME, which is malloc'd
 156    and/or realloc'd as necessary and can start out NULL,
 157    and whose size is passed and returned in *SIZE.
 158
 159    Return the number of characters placed in *NAME
 160    if some nonempty sequence was found, otherwise 0.  */
 161
 162 static int
 163 readname (name, size, stream)
 164      char **name;
 165      int *size;
 166      FILE *stream;
 167 {
 168   int c;
 169   int name_index = 0;
 170
 171   if (*name == NULL)
 172     {
 173       *size = 10;
 174       *name = (char *) xmalloc (*size);
 175     }
 176
 177   /* Skip blank space.  */
 178   while ((c = getc (stream)) != EOF && isspace (c))
 179     /* Do nothing. */ ;
 180
 181   while (c != EOF && !isspace (c))
 182     {
 183       (*name)[name_index++] = c;
 184       while (name_index >= *size)
 185         {
 186           *size *= 2;
 187           *name = (char *) xrealloc (*name, *size);
 188         }
 189       c = getc (stream);
 190     }
 191   (*name)[name_index] = '\0';
 192   return name_index;
 193 }
 194
 195 #ifdef TEST
 196 main ()
 197 {
 198   char *s;
 199
 200   while (s = getusershell ())
 201     puts (s);
 202   exit (0);
 203 }
 204 #endif