Ok, je pense avoir compris. La réponse a déjà été donnée sur le forum : http://www.delphifr.com/forum.v2.aspx?ID=182840

En clair, tu veux rediriger la sortie standard vers ton application
procedure RunDosInMemo(DosApp: string; AMemo: TMemo);
const
  ReadBuffer = 2400;
var
  Security: TSecurityAttributes;
  ReadPipe, WritePipe: THandle;
  start: TStartUpInfo;
  ProcessInfo: TProcessInformation;
  Buffer: Pchar;
  BytesRead: DWord;
  Apprunning: DWord;
begin
  with Security do
  begin
    nlength := SizeOf(TSecurityAttributes);
    binherithandle := true;
    lpsecuritydescriptor := nil;
  end;
  if Createpipe(ReadPipe, WritePipe,
    @Security, 0) then
  begin
    Buffer := AllocMem(ReadBuffer + 1);
    FillChar(Start, Sizeof(Start), #0);
    start.cb := SizeOf(start);
    start.hStdOutput := WritePipe;
    start.hStdInput := ReadPipe;
    start.dwFlags := STARTF_USESTDHANDLES +
      STARTF_USESHOWWINDOW;
    start.wShowWindow := SW_HIDE;

    if CreateProcess(nil,
      PChar(DosApp),
      @Security,
      @Security,
      true,
      NORMAL_PRIORITY_CLASS,
      nil,
      nil,
      start,
      ProcessInfo) then
    begin
      repeat
        Apprunning := WaitForSingleObject
          (ProcessInfo.hProcess, 100);
        Application.ProcessMessages;
      until (Apprunning <> WAIT_TIMEOUT);
      repeat
        BytesRead := 0;
        ReadFile(ReadPipe, Buffer[0],
          ReadBuffer, BytesRead, nil);
        Buffer[BytesRead] := #0;
        OemToAnsi(Buffer, Buffer);
        AMemo.Text := AMemo.text + string(Buffer);
      until (BytesRead < ReadBuffer);
    end;
    FreeMem(Buffer);
    CloseHandle(ProcessInfo.hProcess);
    CloseHandle(ProcessInfo.hThread);
    CloseHandle(ReadPipe);
    CloseHandle(WritePipe);
  end;
end;

procedure TForm1.btnCaptureDosWindowClick(Sender: TObject);
begin
  RunDosInMemo('command.com /C dir c:', Memo1);
end;

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