Maybe this is not the best place to ask, but it's one of the few I know.

Suppose sed ("the stream editor") is released under the GPL v2. Now suppose I build a CGI-based Web site where anyone can input some text and regex. My Web site will take that user input, process it, submit it to sed by means of an 'exec' command, make a few other decisions and output almost exactly whatever sed outputs. My Web site will need some backend code to process user input, submit it to sed and display the result to the visitor.

Question: does that backend code have to be released under the GLP too?

Before you dismiss this question as simple and/or answer it off the top of your head, please consider the very TEXT of the GPL, not your opinion, and read these answers I have found in the official FAQ file.

Some of those answers seem to suggest that no, my Web site code would not be subject to the terms of the GPL because it is a completely independent program:

What is the difference between "mere aggregation" and "combining two modules into one program"?

If a program released under the GPL uses plug-ins, what are the requirements for the licenses of a plug-in?

In what cases is the output of a GPL program covered by the GPL too?

Can I release a non-free program that's designed to load a GPL-covered plug-in?

Can I apply the GPL when writing a plug-in for a non-free program?


But nothing seems so simple anymore after I read these other answers:

A company is running a modified version of a GPL'ed program on a web site. Does the GPL say they must release their modified sources? (This is the worst of all, it kind of says "No, it isn't, but it definitely should be." Well, is it or is it not?

If a library is released under the GPL (not the LGPL), does that mean that any program which uses it has to be under the GPL?

I'd like to incorporate GPL-covered software in my proprietary system. Can I do this by putting a "wrapper" module, under a GPL-compatible lax permissive license (such as the X11 license) in between the GPL-covered part and the proprietary part?

I really don't know what conclusion to take. Do you?

The answer is no, as long as you do not modify the source of sed and you provide links to the real sed then your backend does not need to be open sourced, the only time you have to include the source is when you make changes to that source, since you aren't making any changes to sed, you are not breaking copyright because the GPLv2 clearly states that you only have to provide the changes made to the program which is already under the GPLv2, meaning (if you changed sed in any way, you must provide the source with those changes)

I perfect example of this is the nVidia driver, its not opensource yet interacts with the kernel in such away that it doesnt need to be GPL'd code. nVidia uses a GPL's shim to load a propritary driver into the kernel, they do not need to provide the source to that driver because they are in no way modifying the kernel.

Ask licensing@fsf.org

No, just because you use a GPL program as part of your site doesn't obligate you to GPL everything else involved with your site. Just comply with the GPL with regard to the GPL'ed software and you have no problem.

Where you run into problems is if you take GPL software and try to incorporate it into closed source software. Nothing wrong with having them work together.

WRT networked services, this is the difference between the GPL and the Affero license. (The latter IIRC meaning that code provided over a network service must be released, whereas in the GPL it is not considered redistribution per se and therefore modified sources don't need to be distributed.) Note: I am not a lawyer and specifically not a GNU lawyer especially when it comes to all the complicated crap that got thrown into GPLv3. I prefer the BSD licenses, the simpler the better. And these kinds of questions are exactly why.