Interact with octave using TProcess

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[FangQ]

I want to interact to an octave or matlab session using pipe functions. I read about TProcess from wiki page (http://wiki.freepascal.org/Executing_External_Programs), particularly the example at https://lazarus-ccr.svn.sourceforge.net/svnroot/lazarus-ccr/examples/process/

After some experiments, I wrote the attached code. A button to start an octave process (POctave:TProcess), and then call POctave.Input.Write() to input a user specified command, and  POctave.Output.Read() to get the output.

In my tests, the octave process started fine. However, when I sent the command 'version#10' to the pipe, the Output.Read only returned the copyright info printed at the beginning of octave console. This message ended at "type `news'", not even including the "octave:1>" prompt, not mention the output for "version" command.

I tried the same thing for matlab (started with  "matlab -nojvm -nodesktop"), I got the same results: Output.Read only returned the copyright info, and no more text available no matter what command I send.

I had a feeling that once octave or matlab started its own console, it somehow does not connect to the stdin/stdout/stderr pipes anymore. I am wondering if anyone can help me out on this? I compiled my code on CentOS5.2, with Lazarus 0.9.26 and fpc 2.2.2. My code are attached below.

thank you in advance.

Code:

// start octave process in the background
procedure TForm1.btStartServerClick(Sender: TObject);
begin
     POctave := TProcess.Create(nil);
     if(not POctave.Running) then begin
          POctave.CommandLine:='matlab -nojvm -nodesktop';
          POctave.Options := [poUsePipes];
          mmLog.Lines.Add('-- Executing octave --');
          POctave.Execute;
     end
end;

// input a command from user
procedure TForm1.btRunCommandClick(Sender: TObject);
var
   cmd: String;
begin
     cmd:=InputBox('Input','Please type your command','');
     RunOctaveCommand(cmd+'#10');
end;   

// and print the output
procedure TForm1.RunOctaveCommand(cmd: String);
var
    Buffer: string;
    BytesAvailable: DWord;
    BytesRead:LongInt;
    NoMoreOutput: boolean;
begin
   if(POctave.Running) then
      POctave.Input.Write(cmd[1], Length(cmd));

   if(POctave.Running) then
    begin
      BytesAvailable := POctave.Output.NumBytesAvailable;
      BytesRead := 0;
      while BytesAvailable>0 do
      begin
        SetLength(Buffer, BytesAvailable);
        BytesRead := POctave.OutPut.Read(Buffer[1], BytesAvailable);
        mmLog.Text := mmLog.Text + copy(Buffer,1, BytesRead);
        BytesAvailable := POctave.Output.NumBytesAvailable;
        NoMoreOutput := false;
      end;
      if BytesRead>0 then
        mmLog.SelStart := Length(mmLog.Text);
    end;
end;   

[arnoldb]

You are only checking the octave output results very quickly (and one time only).

Try adding a timer to your application with a 5 or 10 ms interval, and put the

Code:

   if(POctave.Running) then
    begin
      BytesAvailable := POctave.Output.NumBytesAvailable;
      BytesRead := 0;
      while BytesAvailable>0 do
      begin
        SetLength(Buffer, BytesAvailable);
        BytesRead := POctave.OutPut.Read(Buffer[1], BytesAvailable);
        mmLog.Text := mmLog.Text + copy(Buffer,1, BytesRead);
        BytesAvailable := POctave.Output.NumBytesAvailable;
        NoMoreOutput := false;
      end;
      if BytesRead>0 then
        mmLog.SelStart := Length(mmLog.Text);
    end;

code in the OnTimer Event.

[FangQ]

You are only checking the octave output results very quickly (and one time only).

Try adding a timer to your application with a 5 or 10 ms interval, and put the

thanks for the reply. I tried what you suggested, but got the same result. Only the header copyright info were printed, nothing more.

I attached my test unit with this post, the unit looks like the following. I appreciate for more suggestions.

Code:

unit calloctave;

{$mode objfpc}{$H+}

interface

uses
  Classes, Process, SysUtils, FileUtil, LResources, Forms, Controls, Graphics, Dialogs,
  StdCtrls, ExtCtrls;

type

  { TForm1 }

  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    mmLog: TMemo;
    POctave : TProcess;
    Timer1: TTimer;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
    procedure Timer1Timer(Sender: TObject);
  private
    { private declarations }
  public
    { public declarations }
  end;

var
  Form1: TForm1;

implementation

{ TForm1 }

procedure TForm1.Button1Click(Sender: TObject);
begin
     POctave := TProcess.Create(nil);
     if(not POctave.Running) then begin
          POctave.CommandLine:='octave';
          POctave.Options := [poUsePipes];
          mmLog.Lines.Add('-- Executing octave --');
          POctave.Execute;
          Timer1.Enabled:=true;
     end
end;

procedure TForm1.Button2Click(Sender: TObject);
var
     cmd: String;
begin
     cmd:=InputBox('Input','Please type your command','');
     cmd:=cmd+'#10';
     if(POctave.Running) then
      POctave.Input.Write(cmd[1], Length(cmd));
end;

procedure TForm1.Button3Click(Sender: TObject);
begin
    if(POctave.Running) then POctave.Terminate(0);
    POctave.Free;
end;

procedure TForm1.Timer1Timer(Sender: TObject);
var
    Buffer: string;
    BytesAvailable: DWord;
    BytesRead:LongInt;
    NoMoreOutput: boolean;
begin
   if(POctave.Running) then
    begin
      BytesAvailable := POctave.Output.NumBytesAvailable;
      BytesRead := 0;
      while BytesAvailable>0 do
      begin
        SetLength(Buffer, BytesAvailable);
        BytesRead := POctave.OutPut.Read(Buffer[1], BytesAvailable);
        mmLog.Text := mmLog.Text + copy(Buffer,1, BytesRead);
        BytesAvailable := POctave.Output.NumBytesAvailable;
        NoMoreOutput := false;
      end;
      if BytesRead>0 then
        mmLog.SelStart := Length(mmLog.Text);
    end;
end;

initialization
  {$I calloctave.lrs}

end.

[FangQ]

now I tend to believe the issue is from TProcess.

I wrote a simple perl script to test the interactive read/write from stdin/stdout, as below

Code:

#!/usr/bin/perl
my $b;
print "begin interactive mode\n";
while(1){
   $b=<STDIN>;
   $b=~s/[\r\n]+$//g;
   if($b eq "quit"){
       last;
   }
   print "you typed: $b\n";
}

I saved this file as test.pl, I ran the above program and execute test.pl, pstree shows that the thread test.pl is a sub-process of my gui, however, no matter what I send to this program via TProcess.Input.Write, nothing I can read out of TProcess.Output, even the first "begin interactive mode" message. Isn't that strange?

Running the example code at https://lazarus-ccr.svn.sourceforge.net/svnroot/lazarus-ccr/examples/process/  gave me the same behavior. Can someone explain?

[Marc]

now I tend to believe the issue is from TProcess.

iirc tprocess cannot execute scripts (it doesn't interepret them, thats something of your shell)

I saved this file as test.pl, I ran the above program and execute test.pl, pstree shows that the thread test.pl is a sub-process of my gui, ...

do you see "test.pl" as subprocess or do you see "/usr/bin/perl ./test.pl" as subprocess ?
If the first try executing "/usr/bin/perl ./test.pl"

[Leledumbo]

Wanna try my OctaveGUI? It uses TProcess and input output mechanism similar to what you're trying to achieve.

[FangQ]

Wanna try my OctaveGUI? It uses TProcess and input output mechanism similar to what you're trying to achieve.

thank you Leledumbo for sharing your code, it looks very promising. However, I am unable to compile it. Lazarus complains about missing uCmdBox, can you tell me where I can find this unit?

thanks

[FangQ]

Wanna try my OctaveGUI? It uses TProcess and input output mechanism similar to what you're trying to achieve.

My stupid. After reading your code, I realized I appended newline incorrectly. After changing cmd+'#10' to cmd+#10, my GUI now works!

thank you so much for showing me your implementation, a working example is really important

[Leledumbo]

Lazarus complains about missing uCmdBox, can you tell me where I can find this unit?

Whoops! Forgot to tell that I'm using TCmdBox component from CmdLine package. Take it from Lazarus CCR.

thank you so much for showing me your implementation, a working example is really important

You're welcome. Glad I can be of help

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