Lets say I design an entertainment app and when I finish the app I realize that there is a lot of fowl language and want to use a GNU library for something like checking for curse words.

Would using a library as such be a problem legally for selling my product later? (or having it as a closed source project)

  • The best answer for something that simple is to avoid the problem. All you are looking for is profanity; use regexes in code you build yourself, or add them to whatever you are using for input validation to prevent XSS attacks and SQL injection. – Tom Mar 23 '16 at 22:38
  • @TomW Regexes are a clbuttically bad idea for this problem. – Olathe Mar 24 '16 at 2:18

Yes and no.

There's two situations to this.

You own all the copyright:

If you own all the copyright, then you're clear. you can license your software under the GPL, sell it, and bring it back to a closed source application later on. There's one detail: If someone has an open source copy of your software, they are entitled to use it subject to terms of the GPL. You can't take back their license.

You do not own all the copyright:

You can sell the product, however, everything has to be under the GPL, and you can't bring it closed source afterwards, especially if you continue to sell it. This is because through selling it, you convey a form of the software, and an offer of source code must accompany it.

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  • so I would have to own the GNU software (such as the profanity filter) in order to ship my app that is using it? – Travis Tubbs Mar 23 '16 at 20:04
  • You can sell GPL that isn't yours, but it must come with an offer of source code - you need to make all the source code available to anyone who requests it. – Zizouz212 Mar 23 '16 at 20:05
  • so what you're saying is that I can sell my app and simply offer the source code of the profanity filter, but keep the rest of the app closed source? – Travis Tubbs Mar 23 '16 at 20:07
  • @TravisTubbs No. The entire app must be open source - this is because the GPL is a strong copyleft open source licence. You need to offer the entire thing, especially if there is code that isn't yours. Do you own all the code? – Zizouz212 Mar 23 '16 at 20:08

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