Selectively merging *parts* of a file with git?

Question

I'm looking to selectively merge parts of a file with git.

I've got two branches -- call them master and changed -- that are one commit apart; if I merge master into changed, it would just fast-forward.

However, I just want to incorporate a number of parts -- within one file -- from changed to master.

Is there a clean way to do this -- e.g. git asking before making each change? Or am I stuck doing it by hand? (Not the end of the world, but I'd prefer not to, and -- yes -- this could have been avoided with more planning on my part -- such is life.)

Answer 1

Try this:

git merge --no-ff --no-commit changed    # Merge in 'changed' but don't commit
git reset <path/to/your/file>            # Reset the stage state but not 
                                         # the working version of the file
git add -p <path/to/your/file>           # Start adding in interactive mode

(Git will prompt you for each hunk; you can split hunks up if necessary.)

git commit                               # Finally commit the merge with only
                                         # the bits you chose to stage

Note, however, that doing this will make Git think that the file is fully merged, so if someone were to then merge in the same branch again, the other changes from that commit would still not be merged in. This may or may not be what you want.

If you need help with the meanings of the various options in git add's interactive mode, see the output of git help add in the "INTERACTIVE MODE" section.