in reply to Setting up 2 way pipe for a command

When it's up to me to implement this, I almost always reach for IPC::Run. The documentation is a bit unwieldy, but once you work through it the implementation is about as straightforward as it can be.
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Re^2: Setting up 2 way pipe for a command
by gw1500se (Beadle) on Jun 30, 2008 at 22:32 UTC
    Thanks for the suggestion. I may have to switch to IPC::Run as I cannot get open2 to work. It seems to block when I try to read the output. I tried setting autoflush for the output but it doesn't seem to help. I should make it clear that I am trying to make this interactive so I need the output for each input (if there is one) while the command is running. I believe there is a 1:1 correspondence between a line into the command and a line out. The line in does what it is supposed to but at that point the script hangs waiting for a line on the output side so the next input line never goes. However, it is possible that there is not a 1:1 correspondence but until I can manage the blocking I won't really know. It appears like pump might do what I need but I have to read up on it more and see some examples.
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Re^2: Setting up 2 way pipe for a command
by gw1500se (Beadle) on Jul 02, 2008 at 22:55 UTC
    I switched to IPC::Run but has not faired any better. I keep getting a premature end error even though there is input data. Here is the relevent code segment I have now after many various iterations: 
    my $h=start(\@cmd,\$in,\$out,\$err);
                while (!eof(FILELIST)) {
                        $thisline=readline(FILELIST);
                        ($thisfile,$thisfilesize)=split(/\t/,$thisline
+);
                        $in="$thisfile\n";
                        $h->pump;
                        while ($h->pumpable) {
                                $h->pump;
                        }
                        if (length($out)>0) {
                                putmsg($out);
                        }
                        $total+=$thisfilesize;
                        $complete=sprintf("%.2f",$total/$dumpsize);
                        putmsg("$complete%\n");
                }
                finish $h;

    [download]
    In one of my iterations I avoided the premature end message however, the script simply quits on the first call of 'pump'. No error message, nothing. Does anyone one see anything obvious? Thanks.
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[d/l]
      Uh... "premature end error"? As in HTTP server error response? If this is indeed the case, try running the thing from the command line, or at least printing a text/plain header somewhere ahead of the block above.

      Maybe on that iteration that didn't puke, the application being run via IPC::Run didn't output anything?

[reply]
        Thanks for the reply. Its the "process ended prematurely" error. Sorry I didn't take the time to look up the error rather than go from poor memory. Perhaps I am misunderstanding how this works but there indeed may not be any output on the first call to 'pump'. However, there is definitely input. I then try to drain any output in the 'pumpable' loop before going on to the next input string. Therefore the way I think it works this condition should never happen unless there is a bug in the 'pumpable' function. If I am misunderstanding, please correct me as that would be the solution to my problem.
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