You can't just work around the GPL by placing a command-line interface as a shim between your code and the function call interface of the GPL'd library. I'm talking about a contrived binary that just calls library functions, forwarding command line parameters to the arguments of that function as necessary.
Oh yes you can. The GPL gets its power from copyright - the rights that the authors of the original software have over their work. It does not and cannot place any restrictions on any software that you write, unless you literally incorporate the GPL'd source or binary into your software, which a CLI interface does not. The same would be true of an RPC interface.
For example, many databases are GPL'd and provide their entire functionality over RPC. Many CLI programs are GPL'd and (of course) provide their entire functionality over CLI. Neither of these cases place GPL obligations on clients, and it's no different for any given library which you wrap with a CLI.
FSF is neither authoritative nor unbiased source for answer to this question. I'd like to see few court cases that have gone through the motions before thinking this subject to be settled.
Now I am not a lawyer, but I think by analogy the FSFs interpretation would also be needed to enforce the CreativeCommons NoDerivatives licenses. Imagine someone creates an interview-based documentary video series on a controversial scientific topic say global warming and releases it under a NoDerivatives license because they are afraid that a clever edit of their videos would present the topic incorrectly and they have made promises to the scientists about how they will and will not present them.
Now imagine that I rather than edit the video files themself create a playlist, in a (fictive?) format which has the ability to play subsequences of the linked files, and then creates a version of the series which presents the complete opposite message of the original. Would a court find this to be a derivative work of the original videos? What if in my need to edit the video I want to insert certain new short sequences, and thus I distribute a second video along with the playlist, but this video is useless in itself since it just contains a number of short clips in sequence. Would this video be considered a derivative work of the original - remember it serves no purpose in itself except along with the playlist and the original? To me it is not clear, but if they are not derivatives, then this will practically render the concept moot. Since most derivatives could potentially be formulated as the original + a diff. Now I would expect in this case that the combination of the playlist + my video file + original series be considered a derivative work, remember that in the arts transferring a work from one format to another (a dramatization for example) is considered to be a derivative work, even if all the actors would be seen on stage to read from the original book.
As I read it, this is the center of the FSFs argument. Now whether this would apply equally to software I do not know. But I have a hard time imagining that copyright is not as easily circumvented as you seem to indicate.
That's a great question. Would this be a derivative work? I suspect the answer is yes, because in your scenario you've effectively shipped a piece of software which creates a derivative work on-the-fly. I guess it's sort of like an analogy of dynamic linking.
The default in copyright is that you have no rights to a copyrightable work. The GPL grants you some right under certain conditions. If the conditions fail to be met, your granted rights are revoked.
As the creators of the GPL license the FSFs widely published opinion is likely to matter to judges evaluating a case. But in the end noone knows outcomes until would come to pass. So seek to minimize legal risks.
Your comment is literally FUD. Copyright law gives the authors of the GPL'd work exactly no rights over your independent work. Distributing a GPL'd binary along side other works cannot have any impact on those other works. (Otherwise every Linux distribution would be in violation). The GPL is built on top of existing copyright laws which simply don't provide that kind of power. So there is no risk because there's no conceivable legal mechanism in copyright law which behaves like you claim.
I think it's pretty obvious that the GPL derives it's power from copyright. Reasoning: If the GPL does not apply, then you don't have any right to anybody else's code (by the Berne Convention), so it gets its power by granting you more rights than you would have had by default. Make sense?
