How to copy a single file's history form an old Git repo to a new repo?

user_355456 0
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I wanted to make my original complicated question much simpler.

I have the following file in a repo:

E:\\a\b\FooOld\foo.java

I copied the file to another directory a few weeks ago with a new repo:

E:\\c\d\FooNew\foo.java

Is there a way to copy the file history of foo.java from the old repo to the new repo?

git
2 Answers

It can be done, in two big steps. Let's say you have a repo A that contains files that you want to be added on a different repo B:

  1. Use git filter-branch to create a clone of repo A containing only the history of the files you want to preserve.

To achieve this, you can take a look at this answer if you need to preserve history of moves and renames, otherwise there are plenty of other answers on Stack Overflow that does that in a simpler way using git filter-branch. Or you can use filter-repo, which seems to be a much faster and simpler approach to re-write history.

Important: Remember to run git filter-branch on a clone of your repo. I also recommend running git remote rm origin on the clone so there is no chance of pushing this stripped version to origin by accident.

  1. Merge stripped A into B. In repo B, do this:

    2.1. Create a remote connection from B to A:

    git remote add repo-A <git repository stripped A directory>;

    2.2. Pull using the option --allow-unrelated-histories. Providing both repos are using the master branch, the following command will merge one repo into another:

    git pull repo-A master --allow-unrelated-histories

    2.3. Remove the remote connection:

    git remote rm repo-A

user_5340060

This is literally impossible, for the simple reason that there is no such thing as "file history" in Git. In Git, the history is simply the set of all commits. If you add commits, you add history. Whatever commits there are, those are the history. And, each commit represents a complete snapshot of all of your files (well, all the files that are in that commit, but that's a bit redundant).

You can ask git log to show you commits that modify some particular file. The way this works is that git log traipses along through history—backwards, through each commit, one at a time, in other words—and compares all the files in this commit to all the files in the previous commit. If the one specific file you're curious about has changed, git log now shows this one commit. Then it moves on—or rather, back—to the previous commit, whether or not it showed this one commit, and shows, or doesn't, that commit using the same rule, and so on.

user_12564520
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