How to create batch file and run it after install is done with Inno Setup?

I want to create a batch file and run it, after the installation is done. I found a tutorial here: https://web.archive.org/web/20240227180634/https://www.codeproject.com/Questions/477984/createplusandpluswriteplusbatchplusfileplusinplusi

So I started to type this bunch of code here into my [Code] section:

function CreateInstallDatabaseBatch(): boolean;
var
  fileName: string;
  line: string;
begin
  Result:= True;
  fileName:= ExpandConstant('{sd}\{#MyAppName}\Temp\installdatabase.bat');
  line:= 'sqlcmd -S ' + srvName + ' -i {sd}\{#MyAppName}\Temp\installdatabase.sql';
  Result:= SaveStringToFile(fileName, line, true);
  exit;
end;

procedure installdb(CurStep: TSetupStep);
begin
  if CurStep=ssDone then
  begin
    CreateInstallDatabaseBatch();
  end;
end;

It compiles without any error and install my package without any errors, but it doesn't create the batch file with that one line. Do I have to add something? I just added the code parts that are showed in the tutorial and edited them a bit (i.e. I just need one line, not lines).

1. The CurStepChanged from the original code is an Inno Setup event function. You cannot rename it.

2. Make sure the {sd}\{#MyAppName}\Temp exists. Why don't you use an installer temporary folder ({tmp}) instead?

3. You have to use the ExpandConstant function to expand the {sd} constant in the {sd}\{#MyAppName}\Temp\installdatabase.sql (just as with the path to the batch file). You should better wrap the path to double-quotes too.

4. For a single command, you do not need to create a batch file. Just run the command directly using the ShellExec function:

procedure CurStepChanged(CurStep: TSetupStep);
var
  Params: string;
  ErrorCode: Integer;
begin
  if CurStep = ssDone then
  begin
    Params :=
      '-S ' + srvName + ' ' +
      '-i "' + ExpandConstant('{sd}\{#MyAppName}\Temp\installdatabase.sql') + '"';
    ShellExec('', 'sqlcmd', Params, '', SW_SHOW, ewWaitUntilTerminated, ErrorCode);
  end;
end;