Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!wuarchive!psuvax1!psuvm!cunyvm!ndsuvm1.bitnet!nu013809
From: NU013809@NDSUVM1.BITNET (Greg Wettstein)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Searching failure of COMMAND.COM
Message-ID: <2882NU013809@NDSUVM1>
Date: 5 Oct 89 13:36:28 GMT
References: <12957@pur-ee.UUCP>
Distribution: usa
Organization: North Dakota Higher Education Computer Network, Fargo, ND
Lines: 64
DISCLAIMER: Author bears full responsibility for contents of this article.

I experienced a similar problem just recently when I was porting GNU Make to
MS-DOS.  The symptoms were very similar to what the previous poster noticed,
make would attempt to spawn a copy of command.com to run a command.  I was
using the spawnve command to execute command.com with the /c switch which tells
command.com to execute its arguement and return to DOS.  The format of the
spawnve function call is MSC 5.1 is:  spawnve(mode, program, argv, envp)

    Where:  mode = Mode to use when spawning, P_WAIT is the only option
                   available in MS-DOS.

            program = Ghe name of the program to be spawned.

            argv = An array of character pointerw which point to the command
                   line arguements.

            envp = An array of character pointers which point to the
                   environment strings to be used by the child process.

The format of the argv strings were as follows:

   argv[0] = "c::command.com"       <---- The name of the program to execute.

   argv[1] = "-c"                   <---- The execute and return switch.

   argv[2] = "dir"                  <---- Command to execute.

   argv[3] = ""                     <---- Null to terminate arguement list.


When command.com was spawned with this arguement list an error was issued
repeatedly which said that an invalid search path was found.  Control then
returned to the daughter copy of command.com.  Typing an exit command would
return control back to MAKE.  Checking the environment revealed that the only
environment strings present were: PATH=  and COMSPEC=:command.com.

I scratched my head a couple of times, checked that the arguements were all
correct before the spawnve call and then started to look for problems.  Those
readers who have been observant have already spotted the problem.  I used a
-c instead of a /c as an arguement string.  Evidently command.com could not
cope with this and exits leaving an essentially empty operating shell.

I don't know for certain if this is happening with the poster's program but the
symptoms are notoriously similar.  Obvious solutions are to:

   1:=>  Check the source code if it is available for a spawn or exec command.

   2:=>  If source is not available check to see if the user can provide any
         type of configuration for how commands are to be spawned, arguements
         etc.

   3:=>  Use one of the programs floating around the net that uses the
         undocumented DOS function to change the current switch character
         setting.  I have heard conflicting reports on whether or not
         command.com checks the current switch character setting before
         parsing command lines passed to it.


Hopefully this information will cast some light on the problem.  I apologize
if people should find this excessively verbose.  This problem cost me some
time and I would like others to avoid it if possible.

                                        As always,
                                        Dr. G.W. Wettstein
                                        NU013809@NDSUVM1