GNU GPL questions

[Bani]

I know this is very off-topic, but does any developer/law person here know what you can do with the GPL? :hi:

Specifically, I want to
1. Redistribute a compiled GNU GPL program (called LilyPond) with a piece of software I might want to sell. At least I don't want to publish the source
2. Generate an input file for LilyPond, then from my program call lilypond, and use the .png file LilyPond generates. Again, I really don't want to publish my source or be stopped from some day making money with this program.

Is that possible/legal? The internet attacks me with walls of legal text whenever I search so I am really really confused I seem to recall that lots of commercial software does almost the same thing with LAME, so it could be possible....

 

[Croga]

There is some commercial software that *can* use LAME but my experience is that you always need to manually download and install LAME for it.

All I know about GPL is that if you use any code under GNU/GPL IN something you write you're automatically bound by the GNU/GPL as well.
Your situation is different though in that you have a piece of software that REQUIRES Lilypond to operate but you don't actually use GNU/GPL code in your own software. That is a very tricky situation.....

Could you rewrite your program to be independant from Lilypond yet able to work with it? 'cause then you would surely be free from GNU/GPL license.
So for example:
User installs your software but not Lilypond. Your software generates the input file for Lilypond and that's it.
User now installs Lilypond and configures your software to trigger Lilypond upon completion of the input file.

This is basically how Exact Audio Copy works together with LAME. EAC will generate a WAV file from an audio CD. If you install LAME and configure EAC then EAC will trigger LAME to convert the WAV into MP3.
I'm quite sure that this way of working doesn't require you to abide by the GNU/GPL license.

 

[Braque]

What you describe doing is fine, Bani.

Just don't link your app against any GPL code.

 

[Bani]

Just realized I haven't expressed my thanks yet <3
Seems like I'll be okay as long as my program doesn't crash without Lilypond installed and I word some things correctly. Great!