bash/builtins/cd.def

This file is cd.def, from which is created cd.c.  It implements the
builtins "cd" and "pwd" in Bash.

Copyright (C) 1987-2024 Free Software Foundation, Inc.

This file is part of GNU Bash, the Bourne Again SHell.

Bash 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.

Bash 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 Bash.  If not, see <http://www.gnu.org/licenses/>.

$PRODUCES cd.c
#include <config.h>

#if defined (HAVE_UNISTD_H)
#  ifdef _MINIX
#    include <sys/types.h>
#  endif
#  include <unistd.h>
#endif

#include "../bashtypes.h"
#include "posixdir.h"
#include "posixstat.h"
#if defined (HAVE_SYS_PARAM_H)
#include <sys/param.h>
#endif
#include <fcntl.h>

#include <stdio.h>

#include "../bashansi.h"
#include "../bashintl.h"

#include <errno.h>
#include <tilde/tilde.h>

#include "../shell.h"
#include "../flags.h"
#include "maxpath.h"
#include "common.h"
#include "bashgetopt.h"

#if !defined (errno)
extern int errno;
#endif /* !errno */

extern const char * const bash_getcwd_errstr;

static int bindpwd (int);
static int setpwd (char *);
static char *resetpwd (char *);
static int change_to_directory (char *, int, int);

static int cdxattr (char *, char **);
static void resetxattr (void);

/* Change this to 1 to get cd spelling correction by default. */
int cdspelling = 0;

int cdable_vars;

static int eflag;	/* file scope so bindpwd() can see it */
static int xattrflag;	/* O_XATTR support for openat */
static int xattrfd = -1;

$BUILTIN cd
$FUNCTION cd_builtin
$SHORT_DOC cd [-L|[-P [-e]]] [-@] [dir]
Change the shell working directory.

Change the current directory to DIR.  The default DIR is the value of the
HOME shell variable. If DIR is "-", it is converted to $OLDPWD.

The variable CDPATH defines the search path for the directory containing
DIR.  Alternative directory names in CDPATH are separated by a colon (:).
A null directory name is the same as the current directory.  If DIR begins
with a slash (/), then CDPATH is not used.

If the directory is not found, and the shell option `cdable_vars' is set,
the word is assumed to be  a variable name.  If that variable has a value,
its value is used for DIR.

Options:
  -L	force symbolic links to be followed: resolve symbolic
		links in DIR after processing instances of `..'
  -P	use the physical directory structure without following
		symbolic links: resolve symbolic links in DIR before
		processing instances of `..'
  -e	if the -P option is supplied, and the current working
		directory cannot be determined successfully, exit with
		a non-zero status
#if defined (O_XATTR)
  -@	on systems that support it, present a file with extended
		attributes as a directory containing the file attributes
#endif

The default is to follow symbolic links, as if `-L' were specified.
`..' is processed by removing the immediately previous pathname component
back to a slash or the beginning of DIR.

Exit Status:
Returns 0 if the directory is changed, and if $PWD is set successfully when
-P is used; non-zero otherwise.
$END

/* Just set $PWD, don't change OLDPWD.  Used by `pwd -P' in posix mode. */
static int
setpwd (char *dirname)
{
  int old_anm;
  SHELL_VAR *tvar;

  old_anm = array_needs_making;
  tvar = bind_variable ("PWD", dirname ? dirname : "", 0);
  if (tvar && readonly_p (tvar))
    return EXECUTION_FAILURE;
  if (tvar && old_anm == 0 && array_needs_making && exported_p (tvar))
    {
      update_export_env_inplace ("PWD=", 4, dirname ? dirname : "");
      array_needs_making = 0;
    }
  return EXECUTION_SUCCESS;
}

static int
bindpwd (int no_symlinks)
{
  char *dirname, *pwdvar;
  int old_anm, r, canon_failed;
  SHELL_VAR *tvar;

  r = sh_chkwrite (EXECUTION_SUCCESS);

#define tcwd the_current_working_directory
  dirname = tcwd ? (no_symlinks ? sh_physpath (tcwd, 0) : tcwd)
  		 : get_working_directory ("cd");
#undef tcwd

  /* If canonicalization fails, reset dirname to the_current_working_directory */
  canon_failed = 0;
  if (dirname == 0)
    {
      canon_failed = 1;
      dirname = the_current_working_directory;
    }

  old_anm = array_needs_making;
  pwdvar = get_string_value ("PWD");

  tvar = bind_variable ("OLDPWD", pwdvar, 0);
  if (tvar == 0 || readonly_p (tvar))
    r = EXECUTION_FAILURE;
  else if (old_anm == 0 && array_needs_making && exported_p (tvar))
    {
      update_export_env_inplace ("OLDPWD=", 7, pwdvar);
      array_needs_making = 0;
    }

  if (setpwd (dirname) == EXECUTION_FAILURE)
    r = EXECUTION_FAILURE;
  if (canon_failed && eflag)
    r = EXECUTION_FAILURE;

  if (dirname && dirname != the_current_working_directory)
    free (dirname);

  return (r);
}

/* Call get_working_directory to reset the value of
   the_current_working_directory () */
static char *
resetpwd (char *caller)
{
  char *tdir;
      
  FREE (the_current_working_directory);
  the_current_working_directory = (char *)NULL;
  tdir = get_working_directory (caller);
  return (tdir);
}

/* return new constructed directory name in *NDIRP */
static int
cdxattr (char *dir, char **ndirp)
{
#if defined (O_XATTR)
  int apfd, fd, r, e;
  char buf[11+40+40];	/* construct new `fake' path for pwd */

  apfd = openat (AT_FDCWD, dir, O_RDONLY|O_NONBLOCK);
  if (apfd < 0)
    return -1;
  fd = openat (apfd, ".", O_XATTR);
  e = errno;
  close (apfd);		/* ignore close error for now */
  errno = e;
  if (fd < 0)
    return -1;
  r = fchdir (fd);	/* assume fchdir exists everywhere with O_XATTR */
  if (r < 0)
    {
      close (fd);
      return -1;
    }
  /* NFSv4 and ZFS extended attribute directories do not have names which are
     visible in the standard Unix directory tree structure.  To ensure we have
     a valid name for $PWD, we synthesize one under /proc, but to keep that
     path valid, we need to keep the file descriptor open as long as we are in
     this directory.  This imposes a certain structure on /proc. */
  if (ndirp)
    {
      sprintf (buf, "/proc/%d/fd/%d", getpid(), fd);
      *ndirp = savestring (buf);
    }

  if (xattrfd >= 0)
    close (xattrfd);
  xattrfd = fd;  

  return r;
#else
  return -1;
#endif
}

/* Clean up the O_XATTR baggage.  Currently only closes xattrfd */
static void
resetxattr (void)
{
#if defined (O_XATTR)
  if (xattrfd >= 0)
    {
      close (xattrfd);
      xattrfd = -1;
    }
#else
  xattrfd = -1;		/* not strictly necessary */
#endif
}

#define LCD_DOVARS	0x001
#define LCD_DOSPELL	0x002
#define LCD_PRINTPATH	0x004
#define LCD_FREEDIRNAME	0x008

/* This builtin is ultimately the way that all user-visible commands should
   change the current working directory.  It is called by cd_to_string (),
   so the programming interface is simple, and it handles errors and
   restrictions properly. */
int
cd_builtin (WORD_LIST *list)
{
  char *dirname, *cdpath, *path, *temp;
  int path_index, no_symlinks, opt, lflag, e;

#if defined (RESTRICTED_SHELL)
  if (restricted)
    {
      sh_restricted ((char *)NULL);
      return (EXECUTION_FAILURE);
    }
#endif /* RESTRICTED_SHELL */

  eflag = 0;
  no_symlinks = no_symbolic_links;
  xattrflag = 0;
  reset_internal_getopt ();
#if defined (O_XATTR)
  while ((opt = internal_getopt (list, "eLP@")) != -1)
#else
  while ((opt = internal_getopt (list, "eLP")) != -1)
#endif
    {
      switch (opt)
	{
	case 'P':
	  no_symlinks = 1;
	  break;
	case 'L':
	  no_symlinks = 0;
	  break;
	case 'e':
	  eflag = 1;
	  break;
#if defined (O_XATTR)
	case '@':
	  xattrflag = 1;
	  break;
#endif
	CASE_HELPOPT;
	default:
	  builtin_usage ();
	  return (EX_USAGE);
	}
    }
  list = loptend;

  lflag = (cdable_vars ? LCD_DOVARS : 0) |
	  ((interactive && cdspelling) ? LCD_DOSPELL : 0);
  if (eflag && no_symlinks == 0)
    eflag = 0;

  if (list == 0)
    {
      /* `cd' without arguments is equivalent to `cd $HOME' */
      dirname = get_string_value ("HOME");	/* POSIX cd step 2 */

      if (dirname == 0)			/* POSIX cd step 1 */
	{
	  builtin_error (_("HOME not set"));
	  return (EXECUTION_FAILURE);
	}
      lflag = 0;
    }
#if defined (CD_COMPLAINS)
  else if (list->next)
    {
      builtin_error (_("too many arguments"));
      return (EX_USAGE);
    }
#endif
  else if (list->word->word[0] == '\0')
    {
      builtin_error (_("null directory"));	/* POSIX cd implementation defined */
      return (EXECUTION_FAILURE);
    }
  else if (list->word->word[0] == '-' && list->word->word[1] == '\0')
    {
      /* This is `cd -', equivalent to `cd $OLDPWD' */
      dirname = get_string_value ("OLDPWD");

      if (dirname == 0)
	{
	  builtin_error (_("OLDPWD not set"));
	  return (EXECUTION_FAILURE);
	}
      lflag = LCD_PRINTPATH;		/* POSIX cd `-' operand */
    }
  else
    dirname = list->word->word;

  if (privileged_mode == 0 && absolute_pathname (dirname) == 0 && (cdpath = get_string_value ("CDPATH")))
    {
      /* Find directory in $CDPATH, POSIX cd step 5. */
      path_index = 0;
      while (path = extract_colon_unit (cdpath, &path_index))
	{
	  /* OPT is 1 if the path element is non-empty */
	  opt = path[0] != '\0';
	  temp = sh_makepath (path, dirname, MP_DOTILDE);
	  free (path);

	  if (change_to_directory (temp, no_symlinks, xattrflag))
	    {
	      /* POSIX.2 says that if a nonempty directory from CDPATH
		 is used to find the directory to change to, the new
		 directory name is echoed to stdout, whether or not
		 the shell is interactive. */
	      if (opt && (path = no_symlinks ? temp : the_current_working_directory))
		printf ("%s\n", path);

	      free (temp);
#if 0
	      /* Posix.2 says that after using CDPATH, the resultant
		 value of $PWD will not contain `.' or `..'. */
	      return (bindpwd (posixly_correct || no_symlinks));
#else
	      return (bindpwd (no_symlinks));
#endif
	    }
	  else
	    free (temp);
	}
    }

  /* When we get here, DIRNAME is the directory to change to.  If we
     chdir successfully, just return. */
  if (change_to_directory (dirname, no_symlinks, xattrflag))
    {
      if (lflag & LCD_PRINTPATH)
	printf ("%s\n", dirname);
      return (bindpwd (no_symlinks));
    }

  /* If the user requests it, then perhaps this is the name of
     a shell variable, whose value contains the directory to
     change to. */
  if (lflag & LCD_DOVARS)
    {
      temp = get_string_value (dirname);
      if (temp && change_to_directory (temp, no_symlinks, xattrflag))
	{
	  printf ("%s\n", temp);
	  return (bindpwd (no_symlinks));
	}
    }

  /* If the user requests it, try to find a directory name similar in
     spelling to the one requested, in case the user made a simple
     typo.  This is similar to the UNIX 8th and 9th Edition shells. */
  if (lflag & LCD_DOSPELL)
    {
      temp = dirspell (dirname);
      if (temp && change_to_directory (temp, no_symlinks, xattrflag))
	{
	  printf ("%s\n", temp);
	  free (temp);
	  return (bindpwd (no_symlinks));
	}
      else
	FREE (temp);
    }

  e = errno;
  temp = printable_filename (dirname, 0);
  builtin_error ("%s: %s", temp, strerror (e));
  if (temp != dirname)
    free (temp);
  /* posix says to return >1 if eflag && no_symlinks?? */
  return (EXECUTION_FAILURE);
}

$BUILTIN pwd
$FUNCTION pwd_builtin
$SHORT_DOC pwd [-LP]
Print the name of the current working directory.

Options:
  -L	print the value of $PWD if it names the current working
		directory
  -P	print the physical directory, without any symbolic links

By default, `pwd' behaves as if `-L' were specified.

Exit Status:
Returns 0 unless an invalid option is given or the current directory
cannot be read.
$END

/* Non-zero means that pwd always prints the physical directory, without
   symbolic links. */
static int verbatim_pwd;

/* Print the name of the current working directory. */
int
pwd_builtin (WORD_LIST *list)
{
  char *directory;
  int opt, pflag;

  verbatim_pwd = no_symbolic_links;
  pflag = 0;
  reset_internal_getopt ();
  while ((opt = internal_getopt (list, "LP")) != -1)
    {
      switch (opt)
	{
	case 'P':
	  verbatim_pwd = pflag = 1;
	  break;
	case 'L':
	  verbatim_pwd = 0;
	  break;
	CASE_HELPOPT;
	default:
	  builtin_usage ();
	  return (EX_USAGE);
	}
    }
  list = loptend;

#define tcwd the_current_working_directory

  directory = tcwd ? (verbatim_pwd ? sh_physpath (tcwd, 0) : tcwd)
		   : get_working_directory ("pwd");

  /* Try again using getcwd() if canonicalization fails (for instance, if
     the file system has changed state underneath bash). */
  if ((tcwd && directory == 0) ||
      (posixly_correct && same_file (".", tcwd, (struct stat *)0, (struct stat *)0) == 0))
    {
      if (directory && directory != tcwd)
        free (directory);
      directory = resetpwd ("pwd");
    }

#undef tcwd

  if (directory)
    {
      opt = EXECUTION_SUCCESS;
      printf ("%s\n", directory);
      /* This is dumb but posix-mandated. */
      if (posixly_correct && pflag)
	opt = setpwd (directory);
      if (directory != the_current_working_directory)
	free (directory);
      return (sh_chkwrite (opt));
    }
  else
    return (EXECUTION_FAILURE);
}

/* Do the work of changing to the directory NEWDIR.  Handle symbolic
   link following, etc.  This function *must* return with
   the_current_working_directory either set to NULL (in which case
   getcwd() will eventually be called), or set to a string corresponding
   to the working directory.  Return 1 on success, 0 on failure. */

static int
change_to_directory (char *newdir, int nolinks, int xattr)
{
  char *t, *tdir, *ndir;
  int err, canon_failed, r, ndlen;

  tdir = (char *)NULL;

  if (the_current_working_directory == 0)
    {
      t = get_working_directory ("chdir");
      FREE (t);
    }

  t = make_absolute (newdir, the_current_working_directory);

  /* TDIR is either the canonicalized absolute pathname of NEWDIR
     (nolinks == 0) or the absolute physical pathname of NEWDIR
     (nolinks != 0). */
  if (t && *t)
    tdir = nolinks ? sh_physpath (t, 0)
		   : sh_canonpath (t, PATH_CHECKDOTDOT|PATH_CHECKEXISTS);
  else
    tdir = NULL;

  ndlen = strlen (newdir);

  /* Use the canonicalized version of NEWDIR, or, if canonicalization
     failed, use the non-canonical form. */
  canon_failed = 0;
  if (tdir && *tdir)
    free (t);
  else
    {
      FREE (tdir);
      tdir = t;
      canon_failed = 1;
    }

  /* In POSIX mode, if we're resolving symlinks logically and sh_canonpath
     returns NULL (because it checks the path, it will return NULL if the
     resolved path doesn't exist), fail immediately. */
#if defined (ENAMETOOLONG)
  if (posixly_correct && nolinks == 0 && canon_failed && (errno != ENAMETOOLONG || ndlen > PATH_MAX))
#else
  if (posixly_correct && nolinks == 0 && canon_failed && ndlen > PATH_MAX)
#endif
    {
#if defined ENAMETOOLONG
      if (errno != ENOENT && errno != ENAMETOOLONG)
#else
      if (errno != ENOENT)
#endif
	errno = ENOTDIR;
      free (tdir);
      return (0);
    }

#if defined (O_XATTR)
  if (xattrflag)
    {
      r = cdxattr (nolinks ? newdir : tdir, &ndir);
      if (r >= 0)
	{
	  canon_failed = 0;
	  free (tdir);
	  tdir = ndir;
	}
      else
	{
	  err = errno;
	  free (tdir);
	  errno = err;
	  return (0);		/* no xattr */
	}
    }
  else
#endif
    {
      r = chdir (nolinks ? newdir : tdir);
      if (r >= 0)
	resetxattr ();
    }

  /* If the chdir succeeds, update the_current_working_directory. */
  if (r == 0)
    {
      /* If canonicalization failed, but the chdir succeeded, reset the
	 shell's idea of the_current_working_directory. */
      if (canon_failed)
	{
	  t = resetpwd ("cd");
	  if (t == 0)
	    set_working_directory (tdir);
	  else
	    free (t);
	}
      else
	set_working_directory (tdir);

      free (tdir);
      return (1);
    }

  /* We failed to change to the appropriate directory name.  If we tried
     what the user passed (nolinks != 0), punt now. */
  if (nolinks)
    {
      free (tdir);
      return (0);
    }

  err = errno;

  /* We're not in physical mode (nolinks == 0), but we failed to change to
     the canonicalized directory name (TDIR).  Try what the user passed
     verbatim. If we succeed, reinitialize the_current_working_directory. */

  /* The first block is step 9 in the POSIX cd algorithm. */
  if (posixly_correct && ndlen < PATH_MAX && strlen (tdir) >= PATH_MAX)
    r = chdir (newdir);
  else if (posixly_correct == 0)
    r = chdir (newdir);
  else
    r = -1;

  if (r == 0)
    {
      t = resetpwd ("cd");
      if (t == 0)
	set_working_directory (tdir);
      else
	free (t);

      r = 1;
    }
  else
    {
      errno = err;
      r = 0;
    }

  free (tdir);
  return r;
}