You like clean commit histories. If something goes wrong you use
--amend and carry on. Life is good.
Then it hits you, you forgot something in an older commit. So you have to reach for a heavier gun in the form of
git rebase --interactive (or
git rebase -i), which offers a handy
f, fixup <commit> = like "squash", but discard this commit's log message
Let's see this in action. We are starting from this repository with 3 commits:
$ git log --oneline 4e69593 (HEAD -> trunk) Some more work happened ea75734 Some work happened 2a030ce First commit
We now notice that we messed up the second commit (
ea75734). So we fix the problem and make a new commit:
$ git log --oneline 22c85d6 (HEAD -> trunk) Oops 4e69593 Some more work happened ea75734 Some work happened 2a030ce First commit
Now we have to rebase the last 3 commits with
git rebase -i HEAD~3. This will drop us in an editor and list the commits as follows:
pick ea75734 Some work happened pick 4e69593 Some more work happened pick 22c85d6 Oops
We can now reorder them and change "pick" to "fixup" (or "f" for short).
pick ea75734 Some work happened fixup 22c85d6 Oops pick 4e69593 Some more work happened
After saving and exiting the editor, our commit history now is clean (notice the changed commit hashes):
$ git log --oneline 321e945 (HEAD -> trunk) Some more work happened 1b33eb6 Some work happened 2a030ce First commit
While this works, it's a somewhat cumbersome process. But
git offers a convenient alternative in the form of
git commit --fixup.
Let's go back to our previous example and change the "Some work happened" commit once again, but this time with a fixup commit:
git commit --fixup=1b33eb6 [trunk 3e12b6f] fixup! Some work happened
Not only does this automatically generate a commit message, if we now do the same interactive rebasing operation, the fixup commit will automatically be moved to the right position and have "pick" replaced with "fixup".
pick 1b33eb6 Some work happened fixup 3e12b6f fixup! Some work happened pick 321e945 Some more work happened