I already shared git-fetch-file in another comment here, but the .git-remote-files manifests seem a lot nicer than whatever this thing does:

    [file "lib/util.py" from "https://github.com/example/tools.git"]
    commit = a1b2c3d4e5f6789abcdef0123456789abcdef01
    branch = master
    comment = Common utility function

    [file "config.json" from "https://github.com/example/tools.git"]
    commit = b2c3d4e5f6789abcdef0123456789abcdef012
    branch = master
    target = vendor
    comment = Configuration from tools repo

    [file "helper.js" from "https://github.com/another/project.git"]
    commit = c3d4e5f6789abcdef0123456789abcdef0123
    branch = main
    comment = Helper from another project

    core.workflow(
        name = "default",
        origin = git.github_origin(
        url = "https://github.com/google/copybara.git",
        ref = "master",
        ),
        destination = git.destination(
            url = "file:///tmp/foo",
        ),

        # Copy everything but don't remove a README_INTERNAL.txt file if it exists.
        destination_files = glob(["third_party/copybara/**"], exclude = ["README_INTERNAL.txt"]),

        authoring = authoring.pass_thru("Default email <default@default.com>"),
        transformations = [
            core.replace(
                    before = "//third_party/bazel/bashunit",
                    after = "//another/path:bashunit",
                    paths = glob(["**/BUILD"])),
            core.move("", "third_party/copybara")
        ],
    )

There seems to be an absolute ton of reference at https://github.com/google/copybara/blob/master/docs/referenc..., whereas I feel like all the people using git-fetch-file just want files from other repos, and sometimes to make some changes on those.

Google copybara: moving code between repositories