— Function: file-symlink-p filename

If the file filename is a symbolic link, the file-symlink-p function returns the file name to which it is linked. This may be the name of a text file, a directory, or even another symbolic link, or it may be a nonexistent file name.

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, symbolic link, named pipe, terminal, or other I/O device).