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