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25.6.3 Truenames

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.

— Function: file-truename filename

The function file-truename returns the truename of the file filename. The argument must be an absolute file name.

— Function: file-chase-links filename

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.

To illustrate the difference between file-chase-links and 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"

See Buffer File Name, for related information.