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/* getusershell.c -- Return names of valid user shells.
Copyright (C) 1991, 1997, 2000-2001, 2003-2006, 2008-2025 Free Software
Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
/* Written by David MacKenzie <djm@gnu.ai.mit.edu> */
#include <config.h>
/* Specification. */
#include <unistd.h>
#ifndef SHELLS_FILE
# ifndef __DJGPP__
/* File containing a list of nonrestricted shells, one per line. */
# define SHELLS_FILE "/etc/shells"
# else
/* This is a horrible kludge. Isn't there a better way? */
# define SHELLS_FILE "/dev/env/DJDIR/etc/shells"
# endif
#endif
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include "filename.h"
#include "xalloc.h"
#if GNULIB_FOPEN_SAFER
# include "stdio--.h"
#endif
#if ! defined ADDITIONAL_DEFAULT_SHELLS && defined __MSDOS__
# define ADDITIONAL_DEFAULT_SHELLS \
"c:/dos/command.com", "c:/windows/command.com", "c:/command.com",
#else
# define ADDITIONAL_DEFAULT_SHELLS /* empty */
#endif
/* List of shells to use if the shells file is missing. */
static char const* const default_shells[] =
{
ADDITIONAL_DEFAULT_SHELLS
"/bin/sh", "/bin/csh", "/usr/bin/sh", "/usr/bin/csh", NULL
};
/* Index of the next shell in 'default_shells' to return.
0 means we are not using 'default_shells'. */
static size_t default_index = 0;
/* Input stream from the shells file. */
static FILE *shellstream = NULL;
/* Line of input from the shells file. */
static char *line = NULL;
/* Number of bytes allocated for 'line'. */
static size_t line_size = 0;
/* Return an entry from the shells file, ignoring comment lines.
If the file doesn't exist, use the list in DEFAULT_SHELLS (above).
In any case, the returned string is in memory allocated through malloc.
Return NULL if there are no more entries. */
char *
getusershell (void)
{
if (default_index > 0)
{
if (default_shells[default_index])
/* Not at the end of the list yet. */
return xstrdup (default_shells[default_index++]);
return NULL;
}
if (shellstream == NULL)
{
shellstream = fopen (SHELLS_FILE, "r");
if (shellstream == NULL)
{
/* No shells file. Use the default list. */
default_index = 1;
return xstrdup (default_shells[0]);
}
}
for (;;)
{
ssize_t nread = getline (&line, &line_size, shellstream);
/* End of file. */
if (nread == -1)
return NULL;
/* Skip empty lines. */
else if (nread > 1)
{
char *start = line;
char *comment = strchr (start, '#');
char *end;
if (comment != NULL)
{
/* Trim the comment mark. */
*comment = '\0';
end = comment;
}
else
{
/* Trim the newline. */
end = start + nread;
if (end[-1] == '\n')
*--end = '\0';
}
/* Skip leading whitespace. */
while (start < end && isspace ((unsigned char) start[0]))
start++;
/* Trim trailing whitespace. */
while (start < end && isspace ((unsigned char) end[-1]))
*--end = '\0';
/* Only return absolute file names. */
if (start < end && IS_ABSOLUTE_FILE_NAME (start))
return start;
}
}
}
/* Rewind the shells file. */
void
setusershell (void)
{
default_index = 0;
if (shellstream)
rewind (shellstream);
}
/* Close the shells file. */
void
endusershell (void)
{
if (shellstream)
{
fclose (shellstream);
shellstream = NULL;
}
}
#ifdef TEST
int
main (void)
{
char *s;
while (s = getusershell ())
puts (s);
exit (0);
}
#endif
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