[Lazarus] Run 3 extrenal program, pipeline

[Lukasz Sokol]

On 02/02/2012 11:00, xmldom at seznam.cz wrote:
> Hi, I need run 3 external program and redirected output: first | second | third
> 
> For example: 
>    df -hT | grep -v -E 'tmpfs|ecryptfs' | grep 'sda2'
> it gives
>    /dev/sda2     ext4     19G   11G  7,6G  58% /
> 
> I use this http://wiki.lazarus.freepascal.org/Executing_External_Programs#How_to_redirect_output_with_TProcess sample code. It works fine for  first | second.
> 
> For three programs I try edit it:
> 
> 
> function threePipe(inputA, inputB, inputC: string): string;
> var
>  FirstProcess, SecondProcess, ThirdProcess: TProcess;
>  Buffer: array[0..127] of char;
>  ReadCount: Integer;
>  ReadSize: Integer;
> begin
>  FirstProcess  := TProcess.Create(nil);
>  SecondProcess := TProcess.Create(nil);
>  ThirdProcess := TProcess.Create(nil);
> 
>  FirstProcess.Options  := [poUsePipes];
>  SecondProcess.Options := [poUsePipes];
>  ThirdProcess.Options  := [poUsePipes,poStderrToOutPut];
> 
>  FirstProcess.CommandLine  := inputA;
>  SecondProcess.CommandLine := inputB;
>  ThirdProcess.CommandLine := inputC;
> 
>  FirstProcess.Execute;
>  SecondProcess.Execute;
>  ThirdProcess.Execute;
> 

while (Firstprocess.Running or SecondProcess.Running or ThirdProcess.Running) do
begin
  if Firstprocess.Running then
    begin
      if (FirstProcess.Output.NumbytesAvailable > 0) then 
        begin								
          ReadSize := FirstProcess.Output.NumBytesAvailable;
          if ReadSize > SizeOf(Buffer) then 
            ReadSize := SizeOf(Buffer); 
          ReadCount := FirstProcess.Output.Read(Buffer[0], ReadSize);
          SecondProcess.Input.Write(Buffer[0], ReadCount);
          // at the end of this, we have written max. 128 bytes to SecondProcess' input
        end;  // if no more bytes, we could terminate the FirstProcess but having it here
              // may race when the lot starts: when FirstProcess just started but has no output yet
              // or if for some reason it stops on the way; 
              // some checking for first process's errors may be a good idea too, here.
    end
  else
    SecondProcess.CloseInput;  // when first process ends, input to second also ends

  if SecondProcess.Running then
    begin
      if (SecondProcess.Output.NumBytesAvailable > 0) then
        begin
          ReadSize := SecondProcess.Output.NumBytesAvailable;
          if ReadSize > SizeOf(Buffer) then  
            ReadSize := SizeOf(Buffer);  
          ReadCount := SecondProcess.Output.Read(Buffer[0], ReadSize);
          ThirdProcess.Input.Write(Buffer[0], ReadCount);
        end;
    end
  else
    ThirdProcess.CloseInput;
	
  if ThirdProcess.Running then
    begin
      if (ThirdProcess.Output.NumbytesAvailable >0) then
        begin
          ReadSize := ThirdProcess.Output.NumBytesAvailable;
          if ReadSize > SizeOf(Buffer) then  
            ReadSize := SizeOf(Buffer);  
          if ReadSize > 0 then
            begin
              ReadCount := ThirdProcess.Output.Read(Buffer, ReadSize);
              Write(Copy(Buffer,0, ReadCount));  // i think no writeln, but write (grep gives you ^M on each line IIRC)
            end;
        end;
    end;

end;

>  while FirstProcess.Running or (FirstProcess.Output.NumBytesAvailable > 0) do
>  begin
>    if FirstProcess.Output.NumBytesAvailable > 0 then
>    begin
>      ReadSize := FirstProcess.Output.NumBytesAvailable;
>      if ReadSize > SizeOf(Buffer) then
>        ReadSize := SizeOf(Buffer);
>      ReadCount := FirstProcess.Output.Read(Buffer[0], ReadSize);
>      SecondProcess.Input.Write(Buffer[0], ReadCount);
>    end;
>  end;
>  SecondProcess.CloseInput;
> 
>  while SecondProcess.Running or (SecondProcess.Output.NumBytesAvailable > 0) do
>  begin
>    if SecondProcess.Output.NumBytesAvailable > 0 then
>    begin
>      ReadSize := SecondProcess.Output.NumBytesAvailable;
>      if ReadSize > SizeOf(Buffer) then
>        ReadSize := SizeOf(Buffer);
>      ReadCount := SecondProcess.Output.Read(Buffer[0], ReadSize);
>      ThirdProcess.Input.Write(Buffer[0], ReadCount);
>    end;
>  end;
>  ThirdProcess.CloseInput;
> 
> 
>  while ThirdProcess.Running do
>    Sleep(1);
>  ReadSize := ThirdProcess.Output.NumBytesAvailable;
>  if ReadSize > SizeOf(Buffer) then
>    ReadSize := SizeOf(Buffer);
>  if ReadSize > 0 then
>  begin
>    ReadCount := ThirdProcess.Output.Read(Buffer, ReadSize);
>    //WriteLn(Copy(Buffer,0, ReadCount));
>  end
>  else
>    WriteLn('grep did not find what we searched for. ', ThirdProcess.ExitStatus);
> 

//  here;
>  FirstProcess.Free;
>  SecondProcess.Free;
>  ThirdProcess.Free;
>  threePipe := Copy(Buffer,0, ReadCount); // and this will be nonsense - better have another variable accounting all bytes out from third process
> end;
> 
> 
> 
> But after i call 
>    Label1.Caption:=threePipe('df -hT', 'grep -v -E ''tmpfs|ecryptfs''', 'grep ''sda2''');
> function my application end with infinite loop.
> 
> Where I do an error?
> 

Thought compiled only.

But:
- uses same buffer to pass between stages, adjusts buffer to size between reads, does not
stop to read the whole buffer output from first process or second process, just passes buffer
as it comes