installation - How does output redirection work in Inno Setup?

Question

I saw this question here: How to get an output of an Exec'ed program in Inno Setup?

But I can't get it to work myself, the commented out code are my attempts to make this work, but I resorted to a bat file because I couldn't make my redirection work. CacheInstanceName and CacheInstanceDir are global variable defined elsewhere:

function CheckCacheExists(): Integer;
var
  args: String;
  buffer: String;
  ResultCode: Integer;
begin
  // args := 'qlist ' + CacheInstanceName + ExpandConstant(' nodisplay > {tmp}appcheck.txt');
  // MsgBox(args, mbInformation, MB_OK);
  // Exec(CacheInstanceDir + 'inccontrol.exe', 'qlist ' + CacheInstanceName + ExpandConstant(' nodisplay > "{tmp}appcheck.txt"'), '', SW_SHOW,

  ExtractTemporaryFile('checkup.BAT');
  Exec(ExpandConstant('{tmp}checkup.BAT'), CacheInstanceDir + ' ' + 
    CacheInstanceName + ' ' + ExpandConstant('{tmp}'), '', SW_SHOW,
    ewWaitUntilTerminated, ResultCode);
  LoadStringFromFile(ExpandConstant('{tmp}appcheck.txt'),buffer);
  if Pos('^', buffer) = 0 then
  begin
    Result := 0
  end
  else 
  begin
    Result := 1
  end 
end;

What am I doing wrong?

Answer 1

The output redirection syntax is a feature of the command prompt, not the core Windows APIs. Therefore if you want to redirect output then you need to invoke the command via {cmd} /c actual-command-line > output-file. Don't forget to include quotes where appropriate, as {tmp} (and other constants) may contain spaces.

However, you should strongly consider rewriting whatever is in that batch file into actual code. Anything you can do in a batch file you can do either directly in the Inno script or in a DLL that you call from the script. And this permits you greater control over error checking and the format of whatever data you want to retrieve.