Selectively revert or checkout changes to a file in Git?

Question

Is there a command that allows you to partially undo the changes to a file (or files) in the working directory?

Suppose you have edited a file a lot but you realize that

Answer 1

How many commits do you need to go back and select from? If it's just one, maybe take a branch just before it, checkout the file you committed and then use git add -p to add it how you wanted it. Then you can go back to where you were and checkout the file from your temp branch.

that is:

git checkout -b temp troublesome-commit^
git checkout troublesome-commit -- path/to/file
git add -p path/to/file
git commit -c troublesome-commit
git checkout @{-1}
git checkout temp -- path/to/file
git commit path/to/file
git branch -D temp

Other alternatives include going back and editing the commit with git rebase -i (marking the commit as edit, then doing a git reset HEAD^ and redoing the commit when dropped back into the shell).

If the changes you need to select from are spread over a series of commits, it may be better to extract them as patches (or a patch covering all of them) and hand-edit the patch, taking out the changes you want to keep, and feeding the residual into git apply --reverse.