For a given Git repository, how do I find the path to its index file?

Question

Suppose that I am running a script inside a Git repository and want to access the index file directly. How can I get the path to the index file, in a way that also respects e.g. worktrees?

Answer 1

You can use git rev-parse with the --git-path option. From the man-pages:

       --git-path <path>
           Resolve "$GIT_DIR/<path>" and takes other path relocation variables such as $GIT_OBJECT_DIRECTORY, $GIT_INDEX_FILE... into account. For
           example, if $GIT_OBJECT_DIRECTORY is set to /foo/bar then "git rev-parse --git-path objects/abc" returns /foo/bar/abc.

To get the index file specifically, you can write this:

$ git rev-parse --git-path index
.git/index

This also respects worktrees:

$ git -C /path/to/my-worktree rev-parse --git-path index
/path/to/main/repo/.git/worktrees/my-worktree/index

And respects environment variables like GIT_INDEX_FILE:

$ GIT_INDEX_FILE=foo git -C /path/to/my-worktree rev-parse --git-path index
foo

Note that other solutions, such as manually calculating the .git directory and appending a path, might not work due to the lack of handling the above.