1 /* getusershell.c -- Return names of valid user shells.
2
3 Copyright (C) 1991, 1997, 2000-2001, 2003-2006, 2008-2021 Free Software
4 Foundation, Inc.
5
6 This program is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 3 of the License, or
9 (at your option) any later version.
10
11 This program is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
15
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <https://www.gnu.org/licenses/>. */
18
19 /* Written by David MacKenzie <djm@gnu.ai.mit.edu> */
20
21 #include <config.h>
22
23 /* Specification. */
24 #include <unistd.h>
25
26 #ifndef SHELLS_FILE
27 # ifndef __DJGPP__
28 /* File containing a list of nonrestricted shells, one per line. */
29 # define SHELLS_FILE "/etc/shells"
30 # else
31 /* This is a horrible kludge. Isn't there a better way? */
32 # define SHELLS_FILE "/dev/env/DJDIR/etc/shells"
33 # endif
34 #endif
35
36 #include <stdlib.h>
37 #include <ctype.h>
38
39 #include "stdio--.h"
40 #include "xalloc.h"
41
42 #if GNULIB_GETUSERSHELL_SINGLE_THREAD
43 # include "unlocked-io.h"
44 #endif
45
46 static idx_t readname (char **, idx_t *, FILE *);
47
48 #if ! defined ADDITIONAL_DEFAULT_SHELLS && defined __MSDOS__
49 # define ADDITIONAL_DEFAULT_SHELLS \
50 "c:/dos/command.com", "c:/windows/command.com", "c:/command.com",
51 #else
52 # define ADDITIONAL_DEFAULT_SHELLS /* empty */
53 #endif
54
55 /* List of shells to use if the shells file is missing. */
56 static char const* const default_shells[] =
57 {
58 ADDITIONAL_DEFAULT_SHELLS
59 "/bin/sh", "/bin/csh", "/usr/bin/sh", "/usr/bin/csh", NULL
60 };
61
62 /* Index of the next shell in 'default_shells' to return.
63 0 means we are not using 'default_shells'. */
64 static size_t default_index = 0;
65
66 /* Input stream from the shells file. */
67 static FILE *shellstream = NULL;
68
69 /* Line of input from the shells file. */
70 static char *line = NULL;
71
72 /* Number of bytes allocated for 'line'. */
73 static idx_t line_size = 0;
74
75 /* Return an entry from the shells file, ignoring comment lines.
76 If the file doesn't exist, use the list in DEFAULT_SHELLS (above).
77 In any case, the returned string is in memory allocated through malloc.
78 Return NULL if there are no more entries. */
79
80 char *
getusershell(void)81 getusershell (void)
82 {
83 if (default_index > 0)
84 {
85 if (default_shells[default_index])
86 /* Not at the end of the list yet. */
87 return xstrdup (default_shells[default_index++]);
88 return NULL;
89 }
90
91 if (shellstream == NULL)
92 {
93 shellstream = fopen (SHELLS_FILE, "r");
94 if (shellstream == NULL)
95 {
96 /* No shells file. Use the default list. */
97 default_index = 1;
98 return xstrdup (default_shells[0]);
99 }
100 }
101
102 while (readname (&line, &line_size, shellstream))
103 {
104 if (*line != '#')
105 return line;
106 }
107 return NULL; /* End of file. */
108 }
109
110 /* Rewind the shells file. */
111
112 void
setusershell(void)113 setusershell (void)
114 {
115 default_index = 0;
116 if (shellstream)
117 rewind (shellstream);
118 }
119
120 /* Close the shells file. */
121
122 void
endusershell(void)123 endusershell (void)
124 {
125 if (shellstream)
126 {
127 fclose (shellstream);
128 shellstream = NULL;
129 }
130 }
131
132 /* Read a line from STREAM, removing any newline at the end.
133 Place the result in *NAME, which is malloc'd
134 and/or realloc'd as necessary and can start out NULL,
135 and whose size is passed and returned in *SIZE.
136
137 Return the number of bytes placed in *NAME
138 if some nonempty sequence was found, otherwise 0. */
139
140 static idx_t
readname(char ** name,idx_t * size,FILE * stream)141 readname (char **name, idx_t *size, FILE *stream)
142 {
143 int c;
144 size_t name_index = 0;
145
146 /* Skip blank space. */
147 while ((c = getc (stream)) != EOF && isspace (c))
148 /* Do nothing. */ ;
149
150 for (;;)
151 {
152 if (*size <= name_index)
153 *name = xpalloc (*name, size, 1, -1, sizeof **name);
154 if (c == EOF || isspace (c))
155 break;
156 (*name)[name_index++] = c;
157 c = getc (stream);
158 }
159 (*name)[name_index] = '\0';
160 return name_index;
161 }
162
163 #ifdef TEST
164 int
main(void)165 main (void)
166 {
167 char *s;
168
169 while (s = getusershell ())
170 puts (s);
171 exit (0);
172 }
173 #endif
174