What you describe is possible with a few simple commands. As you wrote batch file, you don't mean ShellScript so Windows CMD only right?

You need to store the filename found in an environment variable and then can do string manipulation on it

%myVar:~-N%

Returns the contents of myVar up to Length - N characters so you could replace N with 4 and then get the filename without “.ini”. Concatenation is also supported by just using set again

set "myVar=%myVar%.obj"

Doing the above in a for loop for each file found and if you want to make sure an corresponding obj file exists, you can also perform an

if exist "%myVar%" (do action here)

cozzie said:
I could write a simple c++ (console) application that does the above per folder

There are a ton of different solutions to perform that, starting with a Powershell script, C# script (available with .NET 5 for example), a make-ish tool up to complex build tools. Take whatever makes your liefe easy and if you are looking for a solution, you might also have a look at what we use in our game engine project on GitHub

This is the kind of task at which scripting languages like Python excel. You might be able to solve this particular problem in a batch file, but the more complex a batch file is, the more likely it is that you'll eventually want to add some functionality that can't be done in a batch file, at which point you'll have to rewrite it in a real language anyway. So why not skip the rewriting by using a real language from the beginning?