Adding GNU license

[matteoredaelli]

GNU license is used by many people for many projects. Please add it.

Regards Matteo

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[willnorris]

You're absolutely right that the GPL is used by many projects. We've recently shifted to using standard SPDX style license identifiers, with the existing "apache", "mit", "bsd" values supported only for compatibility. So for the header you've included, the correct value would be "GPL-3.0-or-later". But then there are quite a few variants... three different versions of the GPL, two versions of the AGPL, and all of them with and without the "or-later" option.

Would using SPDX style headers work in your case, rather than the GPL-suggested header? Many projects are already moving in that direction for per-file license headers. If so, you could do that today with:

addlicense -c "Name" -l "GPL-3.0-or-later" -s .