how to roll back changes in a file in a previous commit in git

Question

Hi,

I made 3 'git commit' but I have not done a 'git push'.

1. commit 1
2. commit 2
   touches fileA
   touches fileB
   touches fileC
3. commit 3

So How can I

1. roll back changes I made in file b for commit 2? (I can't do a 'git checkout -- fileB' anymore since I already 'git commit', how can i roll back my changes?
2. make changes in fileC and make it like part of commit 2? I think I can go and change the file now and then run a 'git rebase -i HEAD~2' Correct?

Answer 1

Use git rebase -i HEAD~2 and edit the second commit.

Answer 2

This should work:

1. git rebase -i HEAD~2
2. in your editor, select the following:

edit 9b86592 commit 2
pick f3907cb commit 3

3. at this point roll back the changes you made in fileB, for example with
   `git checkout <version_you_want>` or by manually editing the file
4. make the changes in fileC you want to be part of commit 2
5. `git add fileB fileC`
6. `git commit --amend`
7. `git rebase --continue`

You may need to resolve merging issues if there are conflicts when git tries to apply commit 3. After you resolve those, run git rebase --continue again.

Answer 3

Assuming that you are on branch master and have a clean tree:

# checkout incorrect commit
git checkout <sha1_of_commit2>

# revert the changes to fileB by checking out the parent version
git checkout HEAD^ -- fileB

# make an amended commit
git commit --amend

# go back to master
git checkout master

# transplant the changes since the bad commit onto the amended commit
git rebase --onto HEAD@{1} <sha1_of_commit2>

Answer 4

This is how I would do it.

Checkout the old version of fileB and commit it

git checkout HEAD~3 -- fileB
git commit -m"fix fileB" fileB

Now rebase to squash in your fix with the old commit

git rebase -i HEAD~3

now move your most recent commit "fix fileB" to be after commit 2, and change the "pick" instruction to "squash", joining the commit changing fileB with the commit resetting it.