How can I mirror a directory in a git repo into another git repo?

I have a directory /amp in RepoA and a RepoB (populated with the contents of /amp initially). I want to mirror any changes to the /amp in RepoA into RepoB.

Is it possible ?

P.S: RepoA contains many other directories. I only want to mirror the /amp dir. Whereas RepoB is only going to have the /amp contents not any other.

Solution

You could use git submodules for this, the first step would be to create a repository from your dir /amp and later use it as a submodule in your other repositories.

To make /amp a repository you could do:

$ cd /path/to/amp
$ git init
$ git add .
$ git commit -m "First commit"

Now let's assume you will be using github, you could publish your repo by doing:

$ git remote add origin git@github.com:<your-user>/amp.git
$ git push -u origin master

Now on repoA and repoB you will need to add the new amp repo as a submodule, this can be done by doing something like this:

$ cd /path/to/repoA
$ git submodule add -b master git@github.com:<you-user>/amp ampMirror

Same for repo repoB

$ cd /path/to/repoB
$ git submodule add -b master git@github.com:<you-user>/amp ampMirror
$ git commit -m "added appMirror submodule"

Notice that the name I am giving to the directory within repoA and repoB is ampMirror but it can be anything you want, indeed you can use the same name by just using:

git submodule add -b master git@github.com:<you-user>/amp

The directory structure would look something like:

repo(A/B)
├── .git/
├── .gitmodules   <-- created after adding the submodule
├── foo
└── ampMirror
    ├── .git/     <-- repo to keep/track changes for app (need to git pull)
    └── foo

Now every time a change is made into your amp repo you will need to update "pull" the changes in your repositories for example:

$ cd /path/to/repoB
$ cd appMirror
$ git pull
$ cd ..    <--- get back to your project root
$ git commit -am "update submodule"

Another way of doing this and become useful if have more than one submodule is:

$ cd /path/to/repo(A/B)
$ git submodule foreach git pull origin master
$ git commit -am "updated submodules"

I hope this can help to give you a better idea.