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/* getusershell.c -- Return names of valid user shells.
Copyright (C) 1991 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., 675 Mass Ave, Cambridge, MA 02139, USA. */
/* Written by David MacKenzie <djm@gnu.ai.mit.edu> */
#ifndef SHELLS_FILE
/* File containing a list of nonrestricted shells, one per line. */
#define SHELLS_FILE "/etc/shells"
#endif
#include <stdio.h>
#include <ctype.h>
#ifdef STDC_HEADERS
#include <stdlib.h>
#else
char *malloc ();
char *realloc ();
#endif
static int readname ();
/* List of shells to use if the shells file is missing. */
static char *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.
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 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 default_shells[0];
}
}
while (readname (&line, &line_size, shellstream))
{
if (*line != '#')
return line;
}
return NULL; /* End of file. */
}
/* Rewind the shells file. */
void
setusershell ()
{
default_index = 0;
if (shellstream == NULL)
shellstream = fopen (SHELLS_FILE, "r");
else
fseek (shellstream, 0L, 0);
}
/* Close the shells file. */
void
endusershell ()
{
if (shellstream)
{
fclose (shellstream);
shellstream = NULL;
}
}
/* Allocate N bytes of memory dynamically, with error checking. */
static char *
xmalloc (n)
unsigned n;
{
char *p;
p = malloc (n);
if (p == 0)
{
fprintf (stderr, "virtual memory exhausted\n");
exit (1);
}
return p;
}
/* Reallocate space P to size N, with error checking. */
static char *
xrealloc (p, n)
char *p;
unsigned n;
{
p = realloc (p, n);
if (p == 0)
{
fprintf (stderr, "virtual memory exhausted\n");
exit (1);
}
return p;
}
/* 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 int
readname (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 TEST
main ()
{
char *s;
while (s = getusershell ())
puts (s);
exit (0);
}
#endif
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