1 files changed, 173 insertions, 0 deletions
diff --git a/lib/getusershell.c b/lib/getusershell.c
new file mode 100644
index 0000000..1d6d9ce
--- /dev/null
+++ b/lib/getusershell.c
@@ -0,0 +1,173 @@
+/* getusershell.c -- Return names of valid user shells.
+
+   Copyright (C) 1991, 1997, 2000-2001, 2003-2006, 2008-2023 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 <stdlib.h>
+#include <ctype.h>
+
+#include "stdio--.h"
+#include "xalloc.h"
+
+#if GNULIB_GETUSERSHELL_SINGLE_THREAD
+# include "unlocked-io.h"
+#endif
+
+static idx_t readname (char **, idx_t *, FILE *);
+
+#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 idx_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]);
+        }
+    }
+
+  while (readname (&line, &line_size, shellstream))
+    {
+      if (*line != '#')
+        return line;
+    }
+  return NULL;                  /* End of file. */
+}
+
+/* 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;
+    }
+}
+
+/* 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 bytes placed in *NAME
+   if some nonempty sequence was found, otherwise 0.  */
+
+static idx_t
+readname (char **name, idx_t *size, FILE *stream)
+{
+  int c;
+  size_t name_index = 0;
+
+  /* Skip blank space.  */
+  while ((c = getc (stream)) != EOF && isspace (c))
+    /* Do nothing. */ ;
+
+  for (;;)
+    {
+      if (*size <= name_index)
+        *name = xpalloc (*name, size, 1, -1, sizeof **name);
+      if (c == EOF || isspace (c))
+        break;
+      (*name)[name_index++] = c;
+      c = getc (stream);
+    }
+  (*name)[name_index] = '\0';
+  return name_index;
+}
+
+#ifdef TEST
+int
+main (void)
+{
+  char *s;
+
+  while (s = getusershell ())
+    puts (s);
+  exit (0);
+}
+#endif