Function: expand-file-name

expand-file-name is a function defined in fileio.c.

Signature

(expand-file-name NAME &optional DEFAULT-DIRECTORY)

Documentation

Convert filename NAME to absolute, and canonicalize it.

Second arg DEFAULT-DIRECTORY is directory to start with if NAME is relative
(does not start with slash or tilde); both the directory name and
a directory's file name are accepted. If DEFAULT-DIRECTORY is nil or missing, the current buffer's value of default-directory is used. NAME should be a string that is a valid file name for the underlying filesystem.

File name components that are . are removed, and so are file name components followed by .., along with the .. itself; note that these simplifications are done without checking the resulting file names in the file system.

Multiple consecutive slashes are collapsed into a single slash, except at the beginning of the file name when they are significant (e.g., UNC file names on MS-Windows.)

An initial "~" in NAME expands to your home directory.

An initial "~USER" in NAME expands to USER's home directory. If USER doesn't exist, "~USER" is not expanded.

To do other file name substitutions, see substitute-in-file-name.

For technical reasons, this function can return correct but non-intuitive results for the root directory; for instance,
(expand-file-name ".." "/") returns "/..". For this reason, use
(directory-file-name (file-name-directory dirname)) to traverse a
filesystem tree, not (expand-file-name ".." dirname). Note: make sure DIRNAME in this example doesn't end in a slash, unless it's the root directory.

Other relevant functions are documented in the file-name group.

View in manual

Probably introduced at or before Emacs version 1.6.

Shortdoc

;; file-name
(expand-file-name "foo" "/tmp/")
    => "/tmp/foo"
  (expand-file-name "foo" "/tmp///")
    => "/tmp/foo"
  (expand-file-name "foo" "/tmp/foo/.././")
    => "/tmp/foo"
  (expand-file-name "~" "/tmp/")
    => "/root"

Source Code

// Defined in /usr/src/emacs/src/fileio.c
// Skipping highlighting due to helpful-max-highlight.
{
  /* These point to SDATA and need to be careful with string-relocation
     during GC (via DECODE_FILE).  */
  char *nm;
  char *nmlim;
  const char *newdir;
  const char *newdirlim;
  /* This should only point to alloca'd data.  */
  char *target;

  ptrdiff_t tlen;
#ifdef DOS_NT
  int drive = 0;
  bool collapse_newdir = true;
  bool is_escaped = 0;
#endif /* DOS_NT */
  ptrdiff_t length, nbytes;
  Lisp_Object handler, result, handled_name;
  bool multibyte;
  Lisp_Object hdir;
  USE_SAFE_ALLOCA;

  CHECK_STRING (name);
  CHECK_STRING_NULL_BYTES (name);

  /* If the file name has special constructs in it,
     call the corresponding file name handler.  */
  handler = Ffind_file_name_handler (name, Qexpand_file_name);
  if (!NILP (handler))
    {
      handled_name = calln (handler, Qexpand_file_name,
			    name, default_directory);
      if (STRINGP (handled_name))
	return handled_name;
      error ("Invalid handler in `file-name-handler-alist'");
    }

  /* As a last resort, we may have to use the root as
     default_directory below.  */
  Lisp_Object root;
#ifdef DOS_NT
      /* "/" is not considered a root directory on DOS_NT, so using it
	 as default_directory causes an infinite recursion in, e.g.,
	 the following:

            (let (default-directory)
	      (expand-file-name "a"))

	 To avoid this, we use the root of the current drive.  */
      root = build_string (emacs_root_dir ());
#else
      root = build_string ("/");
#endif

  /* Use the buffer's default-directory if DEFAULT_DIRECTORY is omitted.  */
  if (NILP (default_directory))
    {
      Lisp_Object dir = BVAR (current_buffer, directory);
      /* The buffer's default-directory should be absolute or should
	 start with `~'.  If it isn't absolute, we replace it by its
	 expansion relative to a known absolute name ABSDIR, which is
	 the invocation-directory if the latter is absolute, or the
	 root otherwise.

	 In case default-directory starts with `~' or `~user', where
	 USER is a valid user name, this correctly expands it (and
	 ABSDIR plays no role).  If USER is not a valid user name, the
	 leading `~' loses its special meaning and is retained as part
	 of the expanded name.  */
      if (STRINGP (dir))
	{
	  if (file_name_absolute_no_tilde_p (dir))
	    {
	      CHECK_STRING_NULL_BYTES (dir);
	      default_directory = dir;
	    }
	  else
	    {
	      Lisp_Object absdir
		= STRINGP (Vinvocation_directory)
		&& file_name_absolute_no_tilde_p (Vinvocation_directory)
		? Vinvocation_directory : root;
	      default_directory = Fexpand_file_name (dir, absdir);
	    }
	}
    }
  if (! STRINGP (default_directory))
    default_directory = root;

  handler = Ffind_file_name_handler (default_directory, Qexpand_file_name);
  if (!NILP (handler))
    {
      handled_name = calln (handler, Qexpand_file_name,
			    name, default_directory);
      if (STRINGP (handled_name))
	return handled_name;
      error ("Invalid handler in `file-name-handler-alist'");
    }

  {
    char *o = SSDATA (default_directory);

    /* Make sure DEFAULT_DIRECTORY is properly expanded.
       It would be better to do this down below where we actually use
       default_directory.  Unfortunately, calling Fexpand_file_name recursively
       could invoke GC, and the strings might be relocated.  This would
       be annoying because we have pointers into strings lying around
       that would need adjusting, and people would add new pointers to
       the code and forget to adjust them, resulting in intermittent bugs.
       Putting this call here avoids all that crud.

       The EQ test avoids infinite recursion.  */
    if (! NILP (default_directory) && !EQ (default_directory, name)
	/* Save time in some common cases - as long as default_directory
	   is not relative, it can be canonicalized with name below (if it
	   is needed at all) without requiring it to be expanded now.  */
#ifdef DOS_NT
	/* Detect MSDOS file names with drive specifiers.  */
	&& ! (IS_DRIVE (o[0]) && IS_DEVICE_SEP (o[1])
	      && IS_DIRECTORY_SEP (o[2]))
	/* Detect escaped file names without drive spec after "/:".
	   These should not be recursively expanded, to avoid
	   including the default directory twice in the expanded
	   result.  */
	&& ! (o[0] == '/' && o[1] == ':')
#ifdef WINDOWSNT
	/* Detect Windows file names in UNC format.  */
	&& ! (IS_DIRECTORY_SEP (o[0]) && IS_DIRECTORY_SEP (o[1]))
#endif
#else /* not DOS_NT */
      /* Detect Unix absolute file names (/... alone is not absolute on
	 DOS or Windows).  */
	&& ! (IS_DIRECTORY_SEP (o[0]))
#endif /* not DOS_NT */
	)
      {
	default_directory = Fexpand_file_name (default_directory, Qnil);

	/* The above expansion might have produced a remote file name,
	   so give the handlers one last chance to DTRT.  This can
	   happen when both NAME and DEFAULT-DIRECTORY arguments are
	   relative file names, and the buffer's default-directory is
	   remote.  */
	handler = Ffind_file_name_handler (default_directory,
					   Qexpand_file_name);
	if (!NILP (handler))
	  {
	    handled_name = calln (handler, Qexpand_file_name,
				  name, default_directory);
	    if (STRINGP (handled_name))
	      return handled_name;
	    error ("Invalid handler in `file-name-handler-alist'");
	  }
      }
  }
  multibyte = STRING_MULTIBYTE (name);
  bool defdir_multibyte = STRING_MULTIBYTE (default_directory);
  if (multibyte != defdir_multibyte)
    {
      /* We want to make both NAME and DEFAULT_DIRECTORY have the same
	 multibyteness.  Strategy:
	 . If either NAME or DEFAULT_DIRECTORY is pure-ASCII, they
	   can be converted to the multibyteness of the other one
	   while keeping the same byte sequence.
	 . If both are non-ASCII, the only safe conversion is to
	   convert the multibyte one to be unibyte, because the
	   reverse conversion potentially adds bytes while raw bytes
	   are converted to their multibyte forms, which we will be
	   unable to account for, since the information about the
	   original multibyteness is lost.  If those additional bytes
	   later leak to system APIs because they are not encoded or
	   because they are converted to unibyte strings by keeping
	   the data, file APIs will fail.

	 Note: One could argue that if we see a multibyte string, it
	 is evidence that file-name decoding was already set up, and
	 we could convert unibyte strings to multibyte using
	 DECODE_FILE.  However, this is risky, because the likes of
	 string_to_multibyte are able of creating multibyte strings
	 without any decoding.  */
      if (multibyte)
	{
	  bool name_ascii_p = SCHARS (name) == SBYTES (name);
	  unsigned char *p = SDATA (default_directory);

	  if (!name_ascii_p)
	    while (*p && ASCII_CHAR_P (*p))
	      p++;
	  if (name_ascii_p || *p != '\0')
	    {
	      /* DEFAULT_DIRECTORY is unibyte and possibly non-ASCII.
		 Make a unibyte string out of NAME, and arrange for
		 the result of this function to be a unibyte string.
		 This is needed during bootstrapping and dumping, when
		 Emacs cannot decode file names, because the locale
		 environment is not set up.  */
	      name = make_unibyte_string (SSDATA (name), SBYTES (name));
	      multibyte = 0;
	    }
	  else
	    {
	      /* NAME is non-ASCII and multibyte, and
		 DEFAULT_DIRECTORY is unibyte and pure-ASCII: make a
		 multibyte string out of DEFAULT_DIRECTORY's data.  */
	      default_directory =
		make_multibyte_string (SSDATA (default_directory),
				       SCHARS (default_directory),
				       SCHARS (default_directory));
	    }
	}
      else
	{
	  unsigned char *p = SDATA (name);

	  while (*p && ASCII_CHAR_P (*p))
	    p++;
	  if (*p == '\0')
	    {
	      /* DEFAULT_DIRECTORY is multibyte and NAME is unibyte
		 and pure-ASCII.  Make a multibyte string out of
		 NAME's data.  */
	      name = make_multibyte_string (SSDATA (name),
					    SCHARS (name), SCHARS (name));
	      multibyte = 1;
	    }
	  else
	    default_directory = make_unibyte_string (SSDATA (default_directory),
						     SBYTES (default_directory));
	}
    }

#ifdef WINDOWSNT
  if (!NILP (Vw32_downcase_file_names))
    default_directory = Fdowncase (default_directory);
#endif

  /* Make a local copy of NAME to protect it from GC in DECODE_FILE below.  */
  SAFE_ALLOCA_STRING (nm, name);
  nmlim = nm + SBYTES (name);

#ifdef DOS_NT
  /* Note if special escape prefix is present, but remove for now.  */
  if (nm[0] == '/' && nm[1] == ':')
    {
      is_escaped = 1;
      nm += 2;
    }

  /* Find and remove drive specifier if present; this makes nm absolute
     even if the rest of the name appears to be relative.  Only look for
     drive specifier at the beginning.  */
  if (IS_DRIVE (nm[0]) && IS_DEVICE_SEP (nm[1]))
    {
      drive = (unsigned char) nm[0];
      nm += 2;
    }

#ifdef WINDOWSNT
  /* If we see "c://somedir", we want to strip the first slash after the
     colon when stripping the drive letter.  Otherwise, this expands to
     "//somedir".  */
  if (drive && IS_DIRECTORY_SEP (nm[0]) && IS_DIRECTORY_SEP (nm[1]))
    nm++;

  /* Discard any previous drive specifier if nm is now in UNC format.  */
  if (IS_DIRECTORY_SEP (nm[0]) && IS_DIRECTORY_SEP (nm[1])
      && !IS_DIRECTORY_SEP (nm[2]))
    drive = 0;
#endif /* WINDOWSNT */
#endif /* DOS_NT */

  /* If nm is absolute, look for `/./' or `/../' or `//''sequences; if
     none are found, we can probably return right away.  We will avoid
     allocating a new string if name is already fully expanded.  */
  if (
      IS_DIRECTORY_SEP (nm[0])
#ifdef MSDOS
      && drive && !is_escaped
#endif
#ifdef WINDOWSNT
      && (drive || IS_DIRECTORY_SEP (nm[1])) && !is_escaped
#endif
      )
    {
      /* If it turns out that the filename we want to return is just a
	 suffix of FILENAME, we don't need to go through and edit
	 things; we just need to construct a new string using data
	 starting at the middle of FILENAME.  If we set LOSE, that
	 means we've discovered that we can't do that cool trick.  */
      bool lose = 0;
      char *p = nm;

      while (*p)
	{
	  /* Since we know the name is absolute, we can assume that each
	     element starts with a "/".  */

	  /* "." and ".." are hairy.  */
	  if (IS_DIRECTORY_SEP (p[0])
	      && p[1] == '.'
	      && (IS_DIRECTORY_SEP (p[2])
		  || p[2] == 0
		  || (p[2] == '.' && (IS_DIRECTORY_SEP (p[3])
				      || p[3] == 0))))
	    lose = 1;
	  /* Replace multiple slashes with a single one, except
	     leave leading "//" alone.  */
	  else if (IS_DIRECTORY_SEP (p[0])
		   && IS_DIRECTORY_SEP (p[1])
		   && (p != nm || IS_DIRECTORY_SEP (p[2])))
	    lose = 1;
	  p++;
	}
      if (!lose)
	{
#ifdef DOS_NT
	  /* Make sure directories are all separated with /, but
	     avoid allocation of a new string when not required. */
	  dostounix_filename (nm);
#ifdef WINDOWSNT
	  if (IS_DIRECTORY_SEP (nm[1]))
	    {
	      if (strcmp (nm, SSDATA (name)) != 0)
		name = make_specified_string (nm, -1, nmlim - nm, multibyte);
	    }
	  else
#endif
	  /* Drive must be set, so this is okay.  */
	  if (strcmp (nm - 2, SSDATA (name)) != 0)
	    {
	      name = make_specified_string (nm, -1, p - nm, multibyte);
	      char temp[] = { DRIVE_LETTER (drive), ':', 0 };
	      AUTO_STRING_WITH_LEN (drive_prefix, temp, 2);
	      name = concat2 (drive_prefix, name);
	    }
#ifdef WINDOWSNT
	  if (!NILP (Vw32_downcase_file_names))
	    name = Fdowncase (name);
#endif
#else /* not DOS_NT */
	  if (strcmp (nm, SSDATA (name)) != 0)
	    name = make_specified_string (nm, -1, nmlim - nm, multibyte);
#endif /* not DOS_NT */
	  SAFE_FREE ();
	  return name;
	}
    }

  /* At this point, nm might or might not be an absolute file name.  We
     need to expand ~ or ~user if present, otherwise prefix nm with
     default_directory if nm is not absolute, and finally collapse /./
     and /foo/../ sequences.

     We set newdir to be the appropriate prefix if one is needed:
       - the relevant user directory if nm starts with ~ or ~user
       - the specified drive's working dir (DOS/NT only) if nm does not
         start with /
       - the value of default_directory.

     Note that these prefixes are not guaranteed to be absolute (except
     for the working dir of a drive).  Therefore, to ensure we always
     return an absolute name, if the final prefix is not absolute we
     append it to the current working directory.  */

  newdir = newdirlim = 0;

  if (nm[0] == '~'		/* prefix ~ */
#ifdef DOS_NT
    && !is_escaped		/* don't expand ~ in escaped file names */
#endif
      )
    {
      if (IS_DIRECTORY_SEP (nm[1])
	  || nm[1] == 0)	/* ~ by itself */
	{
	  Lisp_Object tem;

	  newdir = get_homedir ();
	  nm++;
	  tem = build_string (newdir);
	  newdirlim = newdir + SBYTES (tem);
	  /* get_homedir may return a unibyte string, which will bite us
	     if we expect the directory to be multibyte.  */
	  if (multibyte && !STRING_MULTIBYTE (tem))
	    {
	      hdir = DECODE_FILE (tem);
	      newdir = SSDATA (hdir);
	      newdirlim = newdir + SBYTES (hdir);
	    }
	  else if (!multibyte && STRING_MULTIBYTE (tem))
	    multibyte = 1;
#ifdef DOS_NT
	  collapse_newdir = false;
#endif
	}
      else			/* ~user/filename */
	{
	  char *nmhome = user_homedir (nm + 1);
	  if (nmhome)
	    {
	      ptrdiff_t nmhomelen = strlen (nmhome);
	      newdir = nmhome;
	      newdirlim = newdir + nmhomelen;
	      if (multibyte)
		{
		  AUTO_STRING_WITH_LEN (lisp_nmhome, nmhome, nmhomelen);
		  hdir = DECODE_FILE (lisp_nmhome);
		  newdir = SSDATA (hdir);
		  newdirlim = newdir + SBYTES (hdir);
		}

	      while (*++nm && !IS_DIRECTORY_SEP (*nm))
		continue;
#ifdef DOS_NT
	      collapse_newdir = false;
#endif
	    }

	  /* If we don't find a user of that name, leave the name
	     unchanged.  */
	}
    }

#ifdef DOS_NT
  /* On DOS and Windows, nm is absolute if a drive name was specified;
     use the drive's current directory as the prefix if needed.  */
  if (!newdir && drive)
    {
      /* Get default directory if needed to make nm absolute.  */
      char *adir = NULL;
      if (!IS_DIRECTORY_SEP (nm[0]))
	{
	  adir = SAFE_ALLOCA (MAXPATHLEN + 1);
	  if (!getdefdir (c_toupper (drive) - 'A' + 1, adir))
	    adir = NULL;
	  else if (multibyte)
	    {
	      Lisp_Object tem = build_string (adir);

	      tem = DECODE_FILE (tem);
	      newdirlim = adir + SBYTES (tem);
	      memcpy (adir, SSDATA (tem), SBYTES (tem) + 1);
	    }
	  else
	    newdirlim = adir + strlen (adir);
	}
      if (!adir)
	{
	  /* Either nm starts with /, or drive isn't mounted.  */
	  adir = SAFE_ALLOCA (4);
	  adir[0] = DRIVE_LETTER (drive);
	  adir[1] = ':';
	  adir[2] = '/';
	  adir[3] = 0;
	  newdirlim = adir + 3;
	}
      newdir = adir;
    }
#endif /* DOS_NT */

  /* Finally, if no prefix has been specified and nm is not absolute,
     then it must be expanded relative to default_directory.  */

  if (1
#ifndef DOS_NT
      /* /... alone is not absolute on DOS and Windows.  */
      && !IS_DIRECTORY_SEP (nm[0])
#endif
#ifdef WINDOWSNT
      && !(IS_DIRECTORY_SEP (nm[0]) && IS_DIRECTORY_SEP (nm[1])
	   && !IS_DIRECTORY_SEP (nm[2]))
#endif
      && !newdir)
    {
      newdir = SSDATA (default_directory);
      newdirlim = newdir + SBYTES (default_directory);
#ifdef DOS_NT
      /* Note if special escape prefix is present, but remove for now.  */
      if (newdir[0] == '/' && newdir[1] == ':')
	{
	  is_escaped = 1;
	  newdir += 2;
	}
#endif
    }

#ifdef DOS_NT
  if (newdir)
    {
      /* First ensure newdir is an absolute name.  */
      if (
	  /* Detect MSDOS file names with drive specifiers.  */
	  ! (IS_DRIVE (newdir[0])
	     && IS_DEVICE_SEP (newdir[1]) && IS_DIRECTORY_SEP (newdir[2]))
#ifdef WINDOWSNT
	  /* Detect Windows file names in UNC format.  */
	  && ! (IS_DIRECTORY_SEP (newdir[0]) && IS_DIRECTORY_SEP (newdir[1])
		&& !IS_DIRECTORY_SEP (newdir[2]))
#endif
	  )
	{
	  /* Effectively, let newdir be (expand-file-name newdir cwd).
	     Because of the admonition against calling expand-file-name
	     when we have pointers into lisp strings, we accomplish this
	     indirectly by prepending newdir to nm if necessary, and using
	     cwd (or the wd of newdir's drive) as the new newdir.  */
	  char *adir;
#ifdef WINDOWSNT
	  const int adir_size = MAX_UTF8_PATH;
#else
	  const int adir_size = MAXPATHLEN + 1;
#endif

	  if (IS_DRIVE (newdir[0]) && IS_DEVICE_SEP (newdir[1]))
	    {
	      drive = (unsigned char) newdir[0];
	      newdir += 2;
	    }
	  if (!IS_DIRECTORY_SEP (nm[0]))
	    {
	      ptrdiff_t nmlen = nmlim - nm;
	      ptrdiff_t newdirlen = newdirlim - newdir;
	      char *tmp = SAFE_ALLOCA (newdirlen + file_name_as_directory_slop
				  + nmlen + 1);
	      ptrdiff_t dlen = file_name_as_directory (tmp, newdir, newdirlen,
						       multibyte);
	      memcpy (tmp + dlen, nm, nmlen + 1);
	      nm = tmp;
	      nmlim = nm + dlen + nmlen;
	    }
	  adir = SAFE_ALLOCA (adir_size);
	  if (drive)
	    {
	      if (!getdefdir (c_toupper (drive) - 'A' + 1, adir))
		strcpy (adir, "/");
	    }
	  else
	    getcwd (adir, adir_size);
	  if (multibyte)
	    {
	      Lisp_Object tem = build_string (adir);

	      tem = DECODE_FILE (tem);
	      newdirlim = adir + SBYTES (tem);
	      memcpy (adir, SSDATA (tem), SBYTES (tem) + 1);
	    }
	  else
	    newdirlim = adir + strlen (adir);
	  newdir = adir;
	}

      /* Strip off drive name from prefix, if present.  */
      if (IS_DRIVE (newdir[0]) && IS_DEVICE_SEP (newdir[1]))
	{
	  drive = newdir[0];
	  newdir += 2;
	}

      /* Keep only a prefix from newdir if nm starts with slash
         (//server/share for UNC, nothing otherwise).  */
      if (IS_DIRECTORY_SEP (nm[0]) && collapse_newdir)
	{
#ifdef WINDOWSNT
	  if (IS_DIRECTORY_SEP (newdir[0]) && IS_DIRECTORY_SEP (newdir[1])
	      && !IS_DIRECTORY_SEP (newdir[2]))
	    {
	      char *adir = strcpy (SAFE_ALLOCA (newdirlim - newdir + 1), newdir);
	      char *p = adir + 2;
	      while (*p && !IS_DIRECTORY_SEP (*p)) p++;
	      p++;
	      while (*p && !IS_DIRECTORY_SEP (*p)) p++;
	      *p = 0;
	      newdir = adir;
	      newdirlim = newdir + strlen (adir);
	    }
	  else
#endif
	    newdir = newdirlim = "";
	}
    }
#endif /* DOS_NT */

  /* Ignore any slash at the end of newdir, unless newdir is
     just "/" or "//".  */
  length = newdirlim - newdir;
  while (length > 1 && IS_DIRECTORY_SEP (newdir[length - 1])
	 && ! (length == 2 && IS_DIRECTORY_SEP (newdir[0])))
    length--;

  /* Now concatenate the directory and name to new space in the stack frame.  */
  tlen = length + file_name_as_directory_slop + (nmlim - nm) + 1;
  eassert (tlen >= file_name_as_directory_slop + 1);
#ifdef DOS_NT
  /* Reserve space for drive specifier and escape prefix, since either
     or both may need to be inserted.  (The Microsoft x86 compiler
     produces incorrect code if the following two lines are combined.)  */
  target = SAFE_ALLOCA (tlen + 4);
  target += 4;
#else  /* not DOS_NT */
  target = SAFE_ALLOCA (tlen);
#endif /* not DOS_NT */
  *target = 0;
  nbytes = 0;

  if (newdir)
    {
      if (nm[0] == 0 || IS_DIRECTORY_SEP (nm[0]))
	{
#ifdef DOS_NT
	  /* If newdir is effectively "C:/", then the drive letter will have
	     been stripped and newdir will be "/".  Concatenating with an
	     absolute directory in nm produces "//", which will then be
	     incorrectly treated as a network share.  Ignore newdir in
	     this case (keeping the drive letter).  */
	  if (!(drive && nm[0] && IS_DIRECTORY_SEP (newdir[0])
		&& newdir[1] == '\0'))
#endif
	    {
	      memcpy (target, newdir, length);
	      target[length] = 0;
	      nbytes = length;
	    }
	}
      else
	nbytes = file_name_as_directory (target, newdir, length, multibyte);
    }

  memcpy (target + nbytes, nm, nmlim - nm + 1);

  /* Now canonicalize by removing `//', `/.' and `/foo/..' if they
     appear.  */
  {
    char *p = target;
    char *o = target;

    while (*p)
      {
	if (!IS_DIRECTORY_SEP (*p))
	  {
	    *o++ = *p++;
	  }
	else if (p[1] == '.'
		 && (IS_DIRECTORY_SEP (p[2])
		     || p[2] == 0))
	  {
	    /* If "/." is the entire filename, keep the "/".  Otherwise,
	       just delete the whole "/.".  */
	    if (o == target && p[2] == '\0')
	      *o++ = *p;
	    p += 2;
	  }
	else if (p[1] == '.' && p[2] == '.'
		 /* `/../' is the "superroot" on certain file systems.
		    Turned off on DOS_NT systems because they have no
		    "superroot" and because this causes us to produce
		    file names like "d:/../foo" which fail file-related
		    functions of the underlying OS.  (To reproduce, try a
		    long series of "../../" in default_directory, longer
		    than the number of levels from the root.)  */
#ifndef DOS_NT
		 && o != target
#endif
		 && (IS_DIRECTORY_SEP (p[3]) || p[3] == 0))
	  {
#ifdef WINDOWSNT
	    char *prev_o = o;
#endif
	    while (o != target && (--o, !IS_DIRECTORY_SEP (*o)))
	      continue;
#ifdef WINDOWSNT
	    /* Don't go below server level in UNC filenames.  */
	    if (o == target + 1 && IS_DIRECTORY_SEP (*o)
		&& IS_DIRECTORY_SEP (*target))
	      o = prev_o;
	    else
#endif
	    /* Keep initial / only if this is the whole name.  */
	    if (o == target && IS_ANY_SEP (*o) && p[3] == 0)
	      ++o;
	    p += 3;
	  }
	else if (IS_DIRECTORY_SEP (p[1])
		 && (p != target || IS_DIRECTORY_SEP (p[2])))
	  /* Collapse multiple "/", except leave leading "//" alone.  */
	  p++;
	else
	  {
	    *o++ = *p++;
	  }
      }

#ifdef DOS_NT
    /* At last, set drive name.  */
#ifdef WINDOWSNT
    /* Except for network file name.  */
    if (!(IS_DIRECTORY_SEP (target[0]) && IS_DIRECTORY_SEP (target[1])))
#endif /* WINDOWSNT */
      {
	if (!drive) emacs_abort ();
	target -= 2;
	target[0] = DRIVE_LETTER (drive);
	target[1] = ':';
      }
    /* Reinsert the escape prefix if required.  */
    if (is_escaped)
      {
	target -= 2;
	target[0] = '/';
	target[1] = ':';
      }
    result = make_specified_string (target, -1, o - target, multibyte);
    dostounix_filename (SSDATA (result));
#ifdef WINDOWSNT
    if (!NILP (Vw32_downcase_file_names))
      result = Fdowncase (result);
#endif
#else  /* !DOS_NT */
    result = make_specified_string (target, -1, o - target, multibyte);
#endif /* !DOS_NT */
  }

  /* Again look to see if the file name has special constructs in it
     and perhaps call the corresponding file name handler.  This is needed
     for filenames such as "/foo/../user@host:/bar/../baz".  Expanding
     the ".." component gives us "/user@host:/bar/../baz" which needs
     to be expanded again.  */
  handler = Ffind_file_name_handler (result, Qexpand_file_name);
  if (!NILP (handler))
    {
      handled_name = calln (handler, Qexpand_file_name,
			    result, default_directory);
      if (! STRINGP (handled_name))
	error ("Invalid handler in `file-name-handler-alist'");
      result = handled_name;
    }

  SAFE_FREE ();
  return result;
}