Your best bet is to contact the maintainer (he's know to be very responsive) and ask for a clarification of the license.

BTW you have to check the license of every module that you use, not just Tk.

Update: Found it now, it was just in a non-standard location. It's ini Tk/license.terms and says:

The authors hereby grant permission to use, copy, modify, distribute, and license this software and its documentation for any purpose, provided that existing copyright notices are retained in all copies and that this notice is included verbatim in any distributions. No written agreement, license, or royalty fee is required for any of the authorized uses. Modifications to this software may be copyrighted by their authors and need not follow the licensing terms described here, provided that the new terms are clearly indicated on the first page of each file where they apply.

So, in general, one can say: I am allowed to do as I described - as long as I check the licenses on every module I use and as long as I do a copyright note with all the used-modules authors (if the license is as above). Right?

I can't give you legal advise (it's illegal in Germany unless you're an attorney), all I can do is quote some files and hope that you understand them as intended.

If you don't understand the license texts, it's best to consult an attorney anyway - relying on answers in internet forums isn't a very good idea when it comes to jurisdiction.

Your best bet is to put a copyright on your work, have your clients sign an agreement not to sell or give your program away, then charge consultant fees for installation, maintenance, training, etc. Give the program for free, but charge for installing/ consulting on it. Free software can have an advantage..... you can put a clause in the software that you are limited in liability to the cost. :-)

Every so often there is an article in Wired about changing economies, and offering items for free. Chris Anderson talks about it in Wired 16.03. I couldn't find the article on line, however his blog is here.

Note, I'm not advertising for him or anything, I just thought the article and his approach is interesting. FWIW.


tubaandy

It is safe to say that you should follow the license under which perl itself is.

I would for myself restate the question - Could I sell perl without source, with some limitations- charge for it?

No.

We write software at work and we make money hacking together systems. We don't sell software or charge for it. We charge for time and we may rent out systems- servers with software.

I think anything in the gist of creating proprietary software, which is what your idea sounds like here- is going to fly into problems. You can still make money with your programs. You'll just have to learn a different way of how to do that. It's so much better in the long run.

Besides, anything you can code- I will code. Only mine will be gnu or some other that lets everyone contribute and redistribute with source- so mine will be better than yours very quickly and easily.

With your tactic, the only advantage you can have is that you think you've seen some untapped market share of the industry. It won't remain hidden for long. And you can't compete against all of us.

But we can work together very well.