amending a single file in a past commit in git

Question

I want to fix a file in past commit. This might affect all ascending commits.

Is there an easy way to do that?

Many times when I commit twice I find that I've had error in the first commit, and I wish to fix the error without having to git reset my last good commit.

For clarification, I want to change the actual commit, that is, I want the content of the past commit to be changed. In other words, I want to change history!

Answer 1

If you only want to amend the second to last commit (eg. not long ago, especially not before many branches and merges), then I use this procedure:

1. git checkout -b tmp bad-commit
2. fix the files
3. git commit --amend
4. git rebase tmp master

If you have merges in between, you may wanna try rebase -i -p, but the results may vary.

Answer 2

It looks like:

• a filter-branch (complex command which could do what you want)
• and amend and rebase as described by jpalecek. You will find the same solution slightly more detailed in this other related question.

You can find an example of rebase interactive in this comment: you could then avoid the temporary branch, but again, it is more complex.

I also rebase often to clean up the history of development so that changes are correct and grouped properly.

A made-up example:
I rename function foo to bar and commit it with a comment that says, "renamed foo to bar".
Then I move on to the next feature or fix, and commit that, and move on to the next.
Halfway through that, I find that I missed an instance of foo!
I commit my work in progress (or use git-stash), fix the missing 'foo' and commit that, then use git-rebase --interactive to merge the all the foo fixes together into one clean commit.
If I didn't use git-stash, then I'll use git-commit --amend (another form of rebasing) when I finally finish the feature that was in progress.

When my patches are pushed for review, all the pieces are correct and tell a coherent story. Sometimes I use git-rebase --interactive just to make adjacent temporally-separated changes which affect the same bits, so that changes are in context.