Since UNIX has a tree-like directory structure in which directories
   are as easy to manipulate as ordinary files, it is useful to expand
   the FTP servers on these machines to include commands which deal with
   the creation of directories.  Since there are other hosts on the
   ARPA-Internet which have tree-like directories (including TOPS-20 and
   Multics), these commands are as general as possible.

      Four directory commands have been added to FTP:

         MKD pathname

            Make a directory with the name "pathname".

         RMD pathname

            Remove the directory with the name "pathname".


            Print the current working directory name.


            Change to the parent of the current working directory.

   The  "pathname"  argument should be created (removed) as a
   subdirectory of the current working directory, unless the "pathname"
   string contains sufficient information to specify otherwise to the
   server, e.g., "pathname" is an absolute pathname (in UNIX and
   Multics), or pathname is something like "<abso.lute.path>" to


      The CDUP command is a special case of CWD, and is included to
      simplify the implementation of programs for transferring directory
      trees between operating systems having different syntaxes for
      naming the parent directory.  The reply codes for CDUP be
      identical to the reply codes of CWD.

      The reply codes for RMD be identical to the reply codes for its
      file analogue, DELE.

      The reply codes for MKD, however, are a bit more complicated.  A
      freshly created directory will probably be the object of a future
      CWD command.  Unfortunately, the argument to MKD may not always be
      a suitable argument for CWD.  This is the case, for example, when
      a TOPS-20 subdirectory is created by giving just the subdirectory
      name.  That is, with a TOPS-20 server FTP, the command sequence

         MKD MYDIR
         CWD MYDIR

      will fail.  The new directory may only be referred to by its
      "absolute" name; e.g., if the MKD command above were issued while
      connected to the directory <DFRANKLIN>, the new subdirectory
      could only be referred to by the name <DFRANKLIN.MYDIR>.

      Even on UNIX and Multics, however, the argument given to MKD may
      not be suitable.  If it is a "relative" pathname (i.e., a pathname
      which is interpreted relative to the current directory), the user
      would need to be in the same current directory in order to reach
      the subdirectory.  Depending on the application, this may be
      inconvenient.  It is not very robust in any case.

      To solve these problems, upon successful completion of an MKD
      command, the server should return a line of the form:


      That is, the server will tell the user what string to use when
      referring to the created  directory.  The directory name can
      contain any character; embedded double-quotes should be escaped by
      double-quotes (the "quote-doubling" convention).

      For example, a user connects to the directory /usr/dm, and creates
      a subdirectory, named pathname:

         CWD /usr/dm
         200 directory changed to /usr/dm
         MKD pathname
         257 "/usr/dm/pathname" directory created

      An example with an embedded double quote:

         MKD foo"bar
         257 "/usr/dm/foo""bar" directory created
         CWD /usr/dm/foo"bar
         200 directory changed to /usr/dm/foo"bar

      The prior existence of a subdirectory with the same name is an
      error, and the server must return an "access denied" error reply
      in that case.

         CWD /usr/dm
         200 directory changed to /usr/dm
         MKD pathname
         521-"/usr/dm/pathname" directory already exists;
         521 taking no action.

      The failure replies for MKD are analogous to its file  creating
      cousin, STOR.  Also, an "access denied" return is given if a file
      name with the same name as the subdirectory will conflict with the
      creation of the subdirectory (this is a problem on UNIX, but
      shouldn't be one on TOPS-20).

      Essentially because the PWD command returns the same type of
      information as the successful MKD command, the successful PWD
      command uses the 257 reply code as well.


      Because these commands will be most useful in transferring
      subtrees from one machine to another, carefully observe that the
      argument to MKD is to be interpreted as a sub-directory of  the
      current working directory, unless it contains enough information
      for the destination host to tell otherwise.  A hypothetical
      example of its use in the TOPS-20 world:

         CWD <some.where>
         200 Working directory changed
         MKD overrainbow
         257 "<some.where.overrainbow>" directory created
         CWD overrainbow
         431 No such directory
         CWD <some.where.overrainbow>
         200 Working directory changed

         CWD <some.where>
         200 Working directory changed to <some.where>
         MKD <unambiguous>
         257 "<unambiguous>" directory created
         CWD <unambiguous>

      Note that the first example results in a subdirectory of the
      connected directory.  In contrast, the argument in the second
      example contains enough information for TOPS-20 to tell that  the
      <unambiguous> directory is a top-level directory.  Note also that
      in the first example the user "violated" the protocol by
      attempting to access the freshly created directory with a name
      other than the one returned by TOPS-20.  Problems could have
      resulted in this case had there been an <overrainbow> directory;
      this is an ambiguity inherent in some TOPS-20 implementations.
      Similar considerations apply to the RMD command.  The point is
      this: except where to do so would violate a host's conventions for
      denoting relative versus absolute pathnames, the host should treat
      the operands of the MKD and RMD commands as subdirectories.  The
      257 reply to the MKD command must always contain the absolute
      pathname of the created directory.