From raster@highfiber.com Mon Sep 30 23:08:42 2002
Newsgroups: alt.msdos.batch
Subject: Win95Cmd piping, was: Batch File for Win XP
From: raster@highfiber.com (Charles Dye)
Date: 30 Sep 2002 21:08:42 -0700

On Mon, 30 Sep 2002 15:35:48 +0100, "William Allen"
<newsFR3q2@mayfly13.fsnet.co.uk> wrote:

>c) Using Pipes
>
>You'll find that a direct pipe operation won't work in a Win95cmd
>custom DVM.

Actually, piping *does* work in Win95Cmd with a very trivial tweak.
The problem is so stupid I'm actually ashamed it took me this long
to figure it out.  Here's the scoop:

Win95Cmd, like CMD.EXE and 4NT but unlike COMMAND.COM and 4DOS,
supports true pipes:  both sides of the pipe run simultaneously in
separate command shells.  When a command like

  type c:\autoexec.bat | more

is encountered, Win95Cmd spawns a second command shell as a separate
process, passes it the command-line arguments

  /S /D /c"type c:\autoexec.bat"

and pipes the output from that shell back to the original instance
of Win95Cmd, which in turn runs MORE with input from the pipe.

The second instance of the command shell is launched using the
COMSPEC environment variable -- and therein lies the problem.  In
DOS environments (including Windows 95/98/Me) COMSPEC will point to
a shell like COMMAND.COM or 4DOS, which won't know what to make of
those strange command-line arguments!  If COMSPEC points to Win95Cmd
instead, pipes will function as intended.  The programmer who ported
Win95Cmd really should have made the program record its own pathname
at startup and used *that* to spawn pipe shells, rather than the
COMSPEC variable.

We only want COMSPEC to point to Win95Cmd within that program; it
should point to an MS-DOS shell the rest of the time.  Probably the
simplest way to arrange this is to plug an appropriate SET command
into Win95Cmd's autorun registry key:

  HKEY_LOCAL_MACHINE\Software\Microsoft\Command Processor\AutoRun

Make it a string value, for example

  "set comspec=c:\bin\util\win95cmd.exe"

If the executable is in your search path, you can probably get
away with "set comspec=win95cmd.exe" but I recommend the full form.
While you're in there, you might as well create a doubleword value
named CompletionChar and give it a value of 9, to assign filename
completion to the Tab key like more professional shells.

Once this tweak is made, you can experiment with true piping
instead of the temp-file emulation provided by single-tasking
DOS shells like COMMAND.COM and 4DOS.  Enjoy!

  Microsoft Windows 2000 [Version 4.10.0000]
  (C) Copyright 1985-1999 Microsoft Corp.

  D:\WINDOWS\Desktop>set | sort
  BLASTER=A220 I5 D1 H5 P330 T6 E620
  CMDLINE=win
  COMSPEC=c:\bin\util\win95cmd.exe
  PATH=D:\WINDOWS;D:\WINDOWS\COMMAND;C:\NASM;C:\A86;D:\WINDOWS\BAT;C:\BIN\BAT;
C:\BIN\UTIL;C:\BIN\4DOS;C:\BIN\ELVIS;E:\NU
  PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.JS;.WS
  PROMPT=$p$g
  TEMP=D:\windows\temp
  TMP=d:\windows\temp
  UNZIP=-C
  winbootdir=D:\WINDOWS
  windir=D:\WINDOWS

  D:\WINDOWS\Desktop>


-- 
Charles Dye     raster@highfiber.com