git rebase -i — why is it changing commit hashes?

Question

So I\'m more or less familiar with how rebasing works, but up until recently I usually just did a git rebase -i HEAD~20, and modified whatever needed to be modified

Answer 1

From the rebase doc:

The commits that were previously saved into the temporary area are then reapplied to the current branch, one by one, in order.

When the commits are "reapplied" it's really creating a brand new commit...it's content may be the same, but it will have a different timestamp which is part of how it's SHA is generated...thus the new commits will have a new SHA's.

You can read more about how SHA's are calculated here.