Oh, I hadn't thought of that, my slightly extended code was: 

    $pid=open3($wtr, '>&reader', $err, $cmd);
    waitpid($pid, 0);

    my %Results=();
    while(<$rdr>){
        chomp;
        @temp=split(/\t/);
        if(!exists($Results{$temp[0]}) || $Results{$temp[0]}<$temp[10]
+){
            $Results{$temp[0]}=$temp[10];
        }
    }

[download]

So I take it that I should've used waitpid after I finished "reading" the pipe. Duh(!) Moving waitpid til after <$rdr> worked. Upon reflection, I realized that the output from running this particular file was far larger than any other, and was thus the first to fill the I/O buffer.

In related news, I gave myself a crash course in buffering and also tried using IPC::Run() with pty, and worked too, but which is recommended?

In reply to Re^4: waitpid stalling on one particular file by seaver
in thread waitpid stalling on one particular file by seaver

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