D-ers,

I am attempting to use pipeProcess for interacting with an external process.
My simplified routine can work somewhat. But, trying to print any messages
that process writes to stderr yields the message:

(master) gnuplot > gnuplot_example
core.exception.InvalidMemoryOperationError@src/core/exception.d(647): Invalid memory operation

Simplified code:

    import std.stdio;
    import std.process;

    class Gnuplot {
       ProcessPipes pipe;

       void cmd(string txt){
          pipe.stdin.writeln(txt);
          pipe.stdin.flush();
       }

       this(){
          this.pipe = pipeProcess("/usr/local/bin/gnuplot", Redirect.stdin |
          Redirect.stdout | Redirect.stderr);
       }

       ~this(){
          pipe.stdin.close();
          pipe.stdout.flush();
          pipe.stderr.flush();

          foreach( line ; pipe.stdout.byLine ) writeln("stdout: ", line);
          foreach( line ; pipe.stderr.byLine ) writeln("stderr: ", line);
       }
    }

    void main(){

       auto gp = new Gnuplot();
       gp.cmd("plot sin(x)");
       gp.cmd("pause 2");
       gp.cmd("plot line contains error ... should create output to stderr");
       gp.cmd("quit");
    }

Also, I have found a few examples on similar programs (for example in Adam Ruppe's
D-Cookbook - page 107), which provide some very good information and examples.
But, I do not understand what I am seeing in my program example.

Any pointers are gratefully received. ... especially tutorials or example code

Best Regards,
James

PS You may note that I do not have the line "scope (exit) wait pipe.pid".
Two reasons for this are: I do not understand what this is supposed to do,
and attempts to add this froze my program.

PPS I have seen some of Steven Schveighoffers helpful descriptions about
piped processes and child process hanging with excessive outputs ... this
should not be the case here ... only a handful of bytes might possibly be written.