The truename of a file is the name that you get by following symbolic links at all levels until none remain, then simplifying away ‘.’ and ‘..’ appearing as name components. This results in a sort of canonical name for the file. A file does not always have a unique truename; the number of distinct truenames a file has is equal to the number of hard links to the file. However, truenames are useful because they eliminate symbolic links as a cause of name variation.
This function returns the truename of the file filename. If the
argument is not an absolute file name, this function first expands it
This function does not expand environment variables. Only
substitute-in-file-name does that. See Definition of substitute-in-file-name.
If you may need to follow symbolic links preceding ‘..’
appearing as a name component, call
file-truename without prior
direct or indirect calls to
expand-file-name. Otherwise, the
file name component immediately preceding ‘..’ will be
simplified away before
file-truename is called. To
eliminate the need for a call to
file-truename handles ‘~’ in the same way that
If the target of a symbolic links has remote file name syntax,
file-truename returns it quoted. See Functions that Expand Filenames.
This function follows symbolic links, starting with filename, until it finds a file name which is not the name of a symbolic link. Then it returns that file name. This function does not follow symbolic links at the level of parent directories.
If you specify a number for limit, then after chasing through that many links, the function just returns what it has even if that is still a symbolic link.
To illustrate the difference between
file-truename, suppose that /usr/foo is a symbolic link to
the directory /home/foo, and /home/foo/hello is an
ordinary file (or at least, not a symbolic link) or nonexistent. Then
we would have:
(file-chase-links "/usr/foo/hello") ;; This does not follow the links in the parent directories. ⇒ "/usr/foo/hello" (file-truename "/usr/foo/hello") ;; Assuming that /home is not a symbolic link. ⇒ "/home/foo/hello"
This function returns
t if the files file1 and
file2 name the same file. This is similar to comparing their
truenames, except that remote file names are also handled in an
appropriate manner. If file1 or file2 does not exist, the
return value is unspecified.
Sometimes file names or their parts need to be compared as strings, in
which case it’s important to know whether the underlying filesystem is
case-insensitive. This function returns
t if file
filename is on a case-insensitive filesystem. It always returns
t on MS-DOS and MS-Windows. On Cygwin and macOS,
filesystems may or may not be case-insensitive, and the function tries
to determine case-sensitivity by a runtime test. If the test is
inconclusive, the function returns
t on Cygwin and
Currently this function always returns
nil on platforms other
than MS-DOS, MS-Windows, Cygwin, and macOS. It does not detect
case-insensitivity of mounted filesystems, such as Samba shares or
NFS-mounted Windows volumes. On remote hosts, it assumes
the ‘smb’ method. For all other connection methods, runtime
tests are performed.
This function returns
t if file is a file in directory
dir, or in a subdirectory of dir. It also returns
t if file and dir are the same directory. It
compares the truenames of the two directories. If dir does not
name an existing directory, the return value is
This function determines the responsible VC backend of the given
file. For example, if emacs.c is a file tracked by Git,
(vc-responsible-backend "emacs.c") returns ‘Git’.
Note that if file is a symbolic link,
vc-responsible-backend will not resolve it—the backend of the
symbolic link file itself is reported. To get the backend VC of the
file to which file refers, wrap file with a symbolic link
resolving function such as
(vc-responsible-backend (file-chase-links "emacs.c"))