/* getusershell.c -- Return names of valid user shells.   Copyright (C) 1991, 1997, 2000, 2001 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 2, 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, write to the Free Software Foundation,   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  *//* Written by David MacKenzie <djm@gnu.ai.mit.edu> */#ifdef HAVE_CONFIG_H# include <config.h>#endif#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>#if HAVE_STDLIB_H# include <stdlib.h>#endif#include <ctype.h>#include "unlocked-io.h"#include "xalloc.h"#if defined (STDC_HEADERS) || (!defined (isascii) && !defined (HAVE_ISASCII))# define IN_CTYPE_DOMAIN(c) 1#else# define IN_CTYPE_DOMAIN(c) isascii(c)#endif#define ISSPACE(c) (IN_CTYPE_DOMAIN (c) && isspace (c))static int readname ();#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 int 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 int 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 (){  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]);	}    }  while (readname (&line, &line_size, shellstream))    {      if (*line != '#')	return line;    }  return NULL;			/* End of file. */}/* Rewind the shells file. */voidsetusershell (){  default_index = 0;  if (shellstream)    rewind (shellstream);}/* Close the shells file. */voidendusershell (){  if (shellstream)    {      fclose (shellstream);      shellstream = NULL;    }}/* Read a line from STREAM, removing any newline at the end.   Place the result in *NAME, which is malloc'd   and/or realloc'd as necessary and can start out NULL,   and whose size is passed and returned in *SIZE.   Return the number of characters placed in *NAME   if some nonempty sequence was found, otherwise 0.  */static intreadname (name, size, stream)     char **name;     int *size;     FILE *stream;{  int c;  int name_index = 0;  if (*name == NULL)    {      *size = 10;      *name = (char *) xmalloc (*size);    }  /* Skip blank space.  */  while ((c = getc (stream)) != EOF && ISSPACE (c))    /* Do nothing. */ ;  while (c != EOF && !ISSPACE (c))    {      (*name)[name_index++] = c;      while (name_index >= *size)	{	  *size *= 2;	  *name = (char *) xrealloc (*name, *size);	}      c = getc (stream);    }  (*name)[name_index] = '\0';  return name_index;}#ifdef TESTmain (){  char *s;  while (s = getusershell ())    puts (s);  exit (0);}#endif