How does GPL differ from CC BY-NC-SA?

Question

Am I right that:

Copyleft is not equal to Creative Commons (CC BY-NC-SA "This license lets others remix, adapt, and build upon your work non-commercially, as long as they credit you and license their new creations under the identical terms.") and such copyleft licenses as GPL allows commercial use somehow?
Creative commons license gives rights among others to sell modificated code?
Is the GPL copyleft and doesn't bar commercial use in future versions? The GPL is a copyleft license, as far as I know. But it allows us to commercialize future code modifications without author notification, as I understood it: "A “contributor” is a copyright holder who authorizes use under this License of the Program or a work on which the Program is based. The work thus licensed is called the contributor's “contributor version”.

Comments on the answer in its previous form have been moved to chat; please do not continue the earlier discussion here. Comments continuing discussion may be removed. — MadHatter, May 25 at 11:18
Part of Q 2 (using CC BY NC for code) may have been answered here: opensource.stackexchange.com/questions/11134/… — Brandin, May 25 at 11:33
For Q 1, the way you've phrased the question is potentially confusing "Copyleft is/is not equal to X?". It would make more sense to ask "is X copyleft?" A particular license X could be copyleft or not, depending on which license X we're talking about. — Brandin, May 25 at 11:36
You can sell GPL software but in practice this is nearly impossible. Everyone can get the software for free. Probably you can add Donate link and get money from satisfied users who want to encourage you to continue development (in case you are the author of software). — i486, May 26 at 9:13
The GPL is specifically designed for programs as part of a larger software ecosystem with many contributors, so it has special handling rules for different kinds of derived works to enable reuse. The CC license family anticipates a few use cases and gives authors more choice about how to handle them, but assumes that reuse of works will happen on a case-by-case basis, not en masse (like a Linux distribution that ships thousands of packages). — Simon Richter, May 26 at 9:14

MadHatter · Accepted Answer · 2023-05-25 11:39:12Z

CC BY-NC-SA is a copyleft-style licence (the "SA" bit), but there exist many other copyleft licences besides CC BY-NC-SA. The GPL is pretty clear that selling GPL-covered code is permissible; but it requires that freedom be delivered along with the code.
Nobody's entirely sure what "non-commercial" use, as defined by CC BY-NC-SA, involves, but I think there's general agreement that selling the source or binary versions of covered code isn't permitted. Since it's a share-alike / copyleft-style licence (as you quote above), modified versions can only be conveyed under the same terms, so broadly: no, CC BY-NC-SA doesn't permit selling modified code.
The GPL is a copyleft licence. Since commercialisation of current versions is permitted, as the link above makes clear, it is also permitted for future versions; but again, it restricts the ability of those future developers to hold their customers hostage by refusing to give them the four freedoms.

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