in reply to How to monitor a child process from a perl script

If the pmemd executable in question is this one, then you shoudl be able to ahieve your goal by redirecting the output back to your script through a pipe using the piped open.

One Windows the syntax would be something like: 

my $pid = open KID,  '-|', 'pmemd -O con' or die $!;

while( <KID> ) {
     kill 'INT', $pid if m[some data];
}

[download]

On *nix, you'd probably use something like tty (or pty?) instead of con to direct the output through the pipe.

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Re^2: How to monitor a child process from a perl script
by oscarjiao (Novice) on Aug 13, 2009 at 04:31 UTC
    Yes, you are right about the pmemd. However it has multiple output files. The whole command looks something like this:

    pmemd -i mdin -c inpcrd -p prmtop -r restrt -o mdout -x mdcrd

    restrt mdout and mdcrd are outputs while mdout is the one I am going to moniter changes.
    So how do you specify that very file in open?
[reply]
      you are right about the pmemd. However it has multiple output files.

      But you only wish to monitor one of them, right?

      If so, then do as I suggested above, but with the extra options required. And if you need to retain the file (mdout) that would have been produced had you not redirected it, just write it yourself as you monitor the output.

      On Win*, it might look something like: 

      my $pid = open KID,  '-|', 
    'pmemd -i mdin -c inpcrd -p prmtop -r restrt -o con -x mdcrd' 
    or die $!;

open OUT, '>', 'mdout' or die $!;

while( <KID> ) {
    kill 'INT', $pid if m[some data];
    print OUT;
}

      [download]

      Again, I don't know the correct syntax for *nix. Maybe something like this would work?: 

      my $pid = open KID,  '-|', 
    qq[pmemd -i mdin -c inpcrd -p prmtop -r restrt -o /dev/tty -x mdcr
+d] 
    or die $!;

open OUT, '>', 'mdout' or die $!;

while( <KID> ) {
    kill 'INT', $pid if m[some data];
    print OUT;
}

      [download]

      Note the use of the list form of open to avoid a shell process.

      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
[select]
        I don't quite get your code, could you explain little bit to me?

        1. Is KID a Filehandle, which file does it point to?
        2. '-|' allows reading from the output file of pmemd command?
        3. Since I'm using Linux, so what is /dev/tty
[reply]

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