mgibian has asked for the wisdom of the Perl Monks concerning the following question:

I have a fairly sizable perl module that I'm building that contains a large set of function/methods implementing the build and related tasks for a software product. I have a great deal of it working. Late yesterday I ran across the following error which I am having trouble diagnosing: 
Can't spawn "cmd.exe": No error at file.pm line xxx.

[download]
This line is a system function call. What makes this so difficult to understand is the the code at the line in question is no different from similar code just a few lines earlier. Here is a slice of the relevent code, with first the system call that works followed by the system call that is failing: 
      $cstring = $vc6cmd . " " . $project . " " . $cargs;
      @cmd = ("$cstring");
      $status = system("@cmd 1>>$sout 2>&1");

      $cstring = $bldcheck . " vc " . $sout;
      $self->trace("--- $cstring\n");
      @cmd = ("$cstring");
      $status = system("@cmd 1>>$logfile 2>&1");

[download]
Thanks in advance for you assistance in diagnosing this problem. I should note that I am running ActiveState build 806, v5.8.0.

-Marc

Replies are listed 'Best First'.
Re: Can't spawn "cmd.exe": No error at
by eweaverp (Scribe) on Jul 17, 2003 at 18:00 UTC

    Caveat: I'm not a windows or an activestate person, and I don't entirely understand what you're trying to accomplish here.

    But... why are you wrapping $cstring into an array, and then calling the array, if the array only has one member? What if you just:

          $cstring = "$vc6cmd $project $cargs";
      $status = system("$cstring 1>>$sout 2>&1");

      $cstring = "$bldcheck vc $sout";
      $self->trace("--- $cstring\n");
      $status = system("$cstring 1>>$logfile 2>&1");

    [download]

    Is there any reason that wouldn't work too? It's clearer.

    If I were you I would have it print out exactly what is in $cstring, $logfile, et cetera, and try to run the command by hand. That might clear things up slightly? Also, keep in mind that it could be the previous line ($self->trace()) that is causing the real error.

    Hope this is marginally useful...

    ~evan

[reply]
[d/l]
Re: Can't spawn "cmd.exe": No error at
by jsprat (Curate) on Jul 17, 2003 at 18:28 UTC
    What are $vc6cmd and $bldcheck, and why are you stuffing them into an array? I'm guessing (swag) that one is a console program, one is a windows program (which may or may not display a window). Second question, is this a CGI?

    I'm thinking (this time an educated guess) that this is a permissions problem. The user this script is running under doesn't have execute access to cmd.exe.

    anyway, HTH

[reply]
[d/l]
[select]
Re: Can't spawn "cmd.exe": No error at
by traveler (Parson) on Jul 17, 2003 at 20:58 UTC
    I second the earlier requests for more information, but have an additional idea: is it possible that you have exceeded Windows' "process table" or whatever its called? That is, might you have too many processes running? Also, what version of Windows are you using?

    --traveler

[reply]
      Time for a follow up to my original posting...

      First, and more immediately important, I am no longer encountering the problem. I do not say that I have fixed or resolved it, as I am really not sure what was wrong and why it is no longer happening. The only thing I can say is that I copied the system statement from my example, inserted it next to the one that was failing, and then edited it to reflect the few differences between the one that was working and what I needed the failing statement to do. At this point it started working. I do not see WHY it should have started working, nor why it was failing. But the bottom line is that it is now working.

      There was a question as to why I was using the @cmd array variable. I am embarrased to say that it was just sloppiness. I had copied sections of code from various examples around the Internet and apparently had included this extraneous step when I copied the system usage code. I have removed that extra bit of logic and tested things successfully, so thank you for the observation.

      I am running this on both Windows 2000 Pro and Windows XP Pro. The machines themselves are quite big, (System 1 - P4 3.GHz with hyperthreading, 1GB, 800MHz FSB, Serial ATA disks in RAID configuration, 875 chipset ASUS motherboard; System 2 - dual P4 2.2 GHz, 1GB, IDE RAID) so there is no way I should be running into a process table size limitation. Certainly not with the small number of processes I'm using for this build vs. the large number that run when I'm performing some other tasks.

      There are a few things I still need to add to this script set:

      1 - Concurrency - There are steps that can run concurrently, particularly when I'm building bits on other machines (a set of Unix/Linux systems for example). I haven't taken the leap into multi-threading my Perl, though I've done plenty of C/C++ multi-threaded code, so I'm not entirely clueless. I'd appreciate some advise and/or pointers to good example code that I can copy from rather than having to spin my own from scratch.

      2 - Improved logging - right now I have a mishmash of logging going on. Some things get written directly to a "trace" log, things building on remote systems don't get results until the entire build on them has finished when I'd really like to get some interactive feedback of what is happening, some system commands get redirected to their own log file (primarily so their results can be checked), which also makes useful progress reports far more difficult. I'd love some advise and/or pointers on how I might clean this up.

      3 - I need to automate some tasks that actually occur on an MVS system (VSAM+CICS, VSE+CICS, "Started Task+CICS" with some VM sprinkled in). Doing this stuff manually with a "green screen" emulator takes far too long and is much too error prone. But my local MVS system analyst/software developer/administrator keeps telling me it can't be done. I'm sure it CAN be done, though not sure how, and certainly it still could take a LOT of effort. Any advise and/or pointers would be quite appreciated.

      So, thank you everyone for your help. It is invaluable as always, even if in this specific case the initial problem seems rather elusive and has vanished of its own accord.

      -Marc

[reply]

        I do concurrent builds on many different Unix boxes from Windows, not by using threads, but by using remote shell (rsh client comes standard with Windows). The remote shell fires off a nohup Unix build script that writes its output to a Unix log file. After starting the Unix build script, the local rsh exits; this puts no strain on my Windows box at all and by firing off builds like this on 10 different Unix boxes, I am getting concurrent Unix builds; and I can check the status of the builds simply by running a remote shell that greps/tails the Unix log files. This whole process is easily automated via a Perl script.

        On a system lacking remote shell (such as MVS perhaps) you might try using CPAN Net::Telnet module to automate everything you currently do by hand via telnet. This is not as nice as rsh because you need to "delay here" and "expect this", but it can be done (I have used this technique to control remote builds and regression tests on remote systems lacking rsh).

[reply]
        2&>error_file is not DOS/WindowsCMD/WhateverSoftCommandPrompt's syntax, it is 2>error_file
        2&>error_file is (I luv) Unix.
        you should always be careful about pasting code that uses system calls, as it is very different between OS'es.
[reply]

Back to Seekers of Perl Wisdom