PC Media 3/PC MEDIA CD03.iso/share/udos/pppd/pppd.doc

Text File | 1990-04-17 | 7.7 KB | 153 lines

____PPPD (Push/Pop Path & Directory)                                  Ver. 3.01

Purpose: Batch file utility.  Allows current drive:\directory and path to
         be pushed (saved) into and later popped (restored) from a file.
         It keeps its data in a file.

Format:        PPPD PUSH
           or
               PPPD POP [M]

         M pops to the master environment as well as the current one.

Remarks: PPPD PUSH causes the current drive, directory and path to be
         placed in a file.  Repeated PPPD PUSHes keep stacking the then-
         current drive, &c. in the file.

         PPPD POP switches to the most recently PUSHed drive:\directory &
         path and removes it from the file.  When it's popped all the data,
         it deletes the file.

         By default, the path is popped into the current active environ-
         ment, the one from which PPPD is called.  This is what you normal-
         ly require.  If you run with an extra layer of COMMAND.COM or any
         other shell (like DESQview), and especially if you do a lot of
         switching shells (stepping through the DOS door in a program, for
         instance), you might want to use the M option.  That makes PPPD
         pop the path into the master environment (the environment belong-
         ing to the lowest layer of DOS) also.

         If you don't know what I'm talking about, don't worry.  Use PPPD
         POP.  If it seems that PPPD isn't restoring the path properly, try
         PPPD POP M.

         To use PPPD in a batch file, first, put a line, PPPD PUSH.  Then
         put your lines setting up and switching to an application, even
         changing the path string; when the application is finished, PPPD
         POP puts the computer back the way it was.

         If something goes wrong (usually an attempt to pop from an empty
         stack file, but possibly insufficient room in the environment for
         the PATH string), PPPD exits, setting the  DOS errorlevel as fol-
         lows:

            0   No error.  Everything went well.

            1   Complete failure.  No data file to pop, couldn't open
                data file to push etc.  Path not popped.

            2   (M option only) Popped path into the active environment
                but couldn't pop it to the master environment.

            3   (M option only) Popped path into the master environment
                but couldn't pop it to the active environment.

            255 Syntax error: (no PUSH or POP, Option other than M, &c.)

         For most purposes, it's probably wise to make sure PPPD starts
         with a fresh stack file at boot-up.  Put a line in AUTOEXEC.BAT to
         DEL C:\STACK3.PPD (or whatever you're using for PPPD's stack).  On
         the other hand, if you make a point to PPPD PUSH just before you
____PPPD (Push/Pop Path & Directory)                                     Page 2

         turn off the computer, PPPD POP in AUTOEXEC.BAT will bring the ma-
         chine up just as you left it.


Why Change the Path?

         Restoring the DOS path string is PPPD's special feature.  Why do
         you need it?  Many people set a path which runs through all the
         directories that contain executable files and never change it.  If
         you use your PC to do just one or two kinds of task and always
         need the whole set of executable files on tap, then you don't need
         to change the path and you don't need PPPD.  (An earlier program
         of mine called "PPD" and several other programs with names like
         "PUSHDIR" and "POPDIR" do all you need.)

         On the other hand, if you do many different kinds of things on
                                          ___         your PC, you probably don't need all the executable files avail-
                  _____         able for every kind of task.  When you're writing letters, you
         really don't need the debugger handy, and you don't need the thes-
         aurus when you're debugging.  The main reason for changing the
         path string, is to keep it short.  DOS will find a program faster
         if the path it has to hunt through is short.  In addition, occa-
         sionally, you may find it convenient to make sure certain files
             ___         are off the path at certain times.

         So, it's useful to change the path when you change tasks.  Nor-
         mally, you'll do it with a batch file or a CED synonym.  PPPD can
         be called from either of these, when you want to make a temporary
         change.  It's especially handy when you're setting up a disk for
         other people who may not be swift about putting things back when
         they depart.


To Customize PPPD's File:

         As supplied, PPPD will build its stack of data in a file called
         STACK3.PPD on the root directory of drive C:.  If this is incon-
         venient, you can change the specification with DEBUG or with a
         disk editor like Peter Norton's NU.  Search the file for "FLAG:".
         Immediately thereafter, begins the filespec.  You should see:

            FLAG:C:\STACK3.PPD

         Leave the FLAG: and change the rest to what you will.  One thing
         is important: after my C:\STACK3.PPD, you'll see a lot of zeros
         (00 - not the character "0", 30).  Your filespec must begin with
         the character next after the colon in "FLAG:" and must not exceed
         the field of zeros.  There must be at least one zero IMMEDIATELY
         after the end of the file spec you insert, thus:

            1. Do not overwrite all the zeros; leave at least one.

            2. If your file spec is shorter than mine, fill out the
               unused parts of the field with zeros.
____PPPD (Push/Pop Path & Directory)                                     Page 3

Notes:   The hard part of this program (getting and setting the path) is
         done by Kim Kokkonen's TPENV.  He distributes it free, and I here-
         by gratefully acknowledge it.

         The routines used in version 2 ff to write to the current active
         environment are modeled on those in Barry Simon's piece in "Lab
                 ___________         Notes," PC Magazine, v8n20, pp 309-14.

Versions:

         2.00 (Nov. 1989) changes the way the POP function works.  Version
             1 popped the path from the data file to the master environ-
             ment.  It was satisfactory if you run with the ordinary single
             layer of COMMAND.COM but not if you operate with an extra
             shell.  Since POP restored the path to the master environment
             only, you wouldn't see it until you EXITed the extra shell.

             Version 2's M option does something to correct that.  The
             ordinary POP function puts the path into the active environ-
             ment (the one active when PPPD is run).  The M option writes
             to the master environment also.  PPPD could still be flummox-
             ed, however, by a sufficiently balled up sequence of shells
             and DOS doors.

         3.00 (Jan. 1990) enlarges the size of the maximum path string that
             can be handled to 254 characters.  The DOS command line can't
             hold more than 128 characters, but it's possible to make a
             longer strings by playing tricks.  Stack file name changed to
             STACK3.PPD to avoid confusion with previous versions.  3.01
             corrects a bug in errorlevel setting.


                                                   R. N. Wisan --April 1990
                                          37 Clinton St., Oneonta, NY 13820