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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

This function returns the truename of the file filename. If the argument is not an absolute file name, this function first expands it against default-directory.

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, you should make sure to call file-truename without prior direct or indirect calls to expand-file-name, as otherwise the file name component immediately preceding ‘..’ will be “simplified away” before file-truename is called. To eliminate the need for a call to expand-file-name, file-truename handles ‘~’ in the same way that expand-file-name does. See Functions that Expand Filenames.

— Function: file-chase-links filename &optional limit

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-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.