I will be writing a GUI for a GPL licensed command line code. The GUI will neither embed, nor link to the code. Instead, it prepares input files for the command line code, and visualizes the output.
My question is this. If I were to commercially release the GUI, would It need to be GPL licensed as well? I apologize if the answer to this should be obvious, I have not personally been able to confidently decipher the implications of this license.
Thank you.
In my opinion, no, you would not need to use the GPL.
See the GPL FAQ
Wikipedia's entry for GPL has a good explanation for this matter: http://en.wikipedia.org/wiki/GNU_General_Public_License#Communicating_and_bundling_with_non-GPL_programs
Especially the parts: "The mere act of communicating with other programs does not, by itself, require all software to be GPL; nor does distributing GPL software with non-GPL software. However, minor conditions must be followed that ensures the rights of GPL software is not restricted."
and:
"By contrast, pipes, sockets and command-line arguments are communication mechanisms normally used between two separate programs. So when they are used for communication, the modules normally are separate programs. But if the semantics of the communication are intimate enough, exchanging complex internal data structures, that too could be a basis to consider the two parts as combined into a larger program."
Software licenses, including the GPL, unfortunately cannot give a solid, 100% proof answer in all cases, so it is up to the programmer to try to figure out what the end result is. IANAL, but I think you might be safe, but this is just my opinion and you can't rely on that!
Edit: An additional link: http://ifross.org/en/program-forks-gpl-licensed-program-system-or-vice-versa-call-derivative-work IFROSS is according to itself "Institute for Legal Questions on Free and Open Source Software" and the explanation there is pretty good, and it says you're clear... maybe.
You should ask a lawyer or the authors of the GPL'd code. As far as I can tell, though, the GPL license doesn't stipulate the license of products which handle the code itself.
If you don't distribute the GPL code (or the derivation you could make of it), the no problem.
But your UI is pretty useless without the GPL project you are talking about right ?
I highly suggest you to contact the author and ask a special authorization.
I'm sure he will be more than happy to have his software used by more people thanks to you.