I have to step back and apologize for being so hard for IDEA.

The problem with the groovy script editing in IDEA is: IDEA doesn't only need a project to know where the classpath and all the required stuff for running and analyzing a groovy file can be found, it also needs a module inside this project, configured to be a groovy module! After that thing is created, I can easily edit my script with code-completion and everything and run it from inside the IDE.

Great! Much better than eclipse as far as I see.

I also tried to use netbeans to get the same thing done. This was worse than eclipse and IDEA - in netbeans, I could not find anything to simply create a groovy project in an existing location - all I could find was a groovy sample project with a lot of stuff in, and the possibility to create a new grails project - way too much to write a simple script...

The next thing I have to tackle is understanding the ant tar libs to get my drupal module files extracted... Allright, it's true, I'm doing a lot of stuff here, for something that I could easily do with a 5 line shell script. But for one, this is totally what I expected, I mainly chose groovy because I want to get deeper into it, and I'm going to add much more things later - downloading the modules/theme files from drupal.org, upgrading, etc.