— Function: file-symlink-p filename

If the file filename is a symbolic link, the file-symlink-p function returns the (non-recursive) link target as a string. (Determining the file name that the link points to from the target is nontrivial.) First, this function recursively follows symbolic links at all levels of parent directories.

If the file filename is not a symbolic link (or there is no such file), file-symlink-p returns nil.

          (file-symlink-p "foo")
               ⇒ nil
          (file-symlink-p "sym-link")
               ⇒ "foo"
          (file-symlink-p "sym-link2")
               ⇒ "sym-link"
          (file-symlink-p "/bin")
               ⇒ "/pub/bin"

— Function: file-directory-p filename

This function returns t if filename is the name of an existing directory, nil otherwise.

          (file-directory-p "~rms")
               ⇒ t
          (file-directory-p "~rms/lewis/files.texi")
               ⇒ nil
          (file-directory-p "~rms/lewis/no-such-file")
               ⇒ nil
          (file-directory-p "$HOME")
               ⇒ nil
          (file-directory-p
           (substitute-in-file-name "$HOME"))
               ⇒ t

— Function: file-regular-p filename

This function returns t if the file filename exists and is a regular file (not a directory, named pipe, terminal, or other I/O device).