How to commit without an index file?

In my program, I have the file paths, permissions and Git object IDs of everything that I want to appear in the next commit. Hence, I want to create a commit without creating an index file.

Essentially it's like to combining `--cacheinfo` from `update-index` with `commit` like:

	git commit \
		-m "Commit message" \
		--branch my-branch \
		--cacheinfo "100644,0123456789abcdef0123456789abcdef01234567,path/to/first/file” \
		--cacheinfo "100755,123456789abcdef0123456789abcdef012345670,path/to/second/file” \
		--cacheinfo "100644,23456789abcdef0123456789abcdef0123456701,path/to/third/file"

In this example, the command would not read the index file, but would get the information necessary to create the commit tree as arguments (or from STDIN). The command would handle recursively creating trees for the intermediate directories. The object ID for the final tree would be used for the `tree` field of the commit.

I tried tricks for simulating standard streams as an index file to Git, but they didn't work out:

	$ GIT_INDEX_FILE=/dev/stdout git read-tree HEAD
	fatal: Unable to create '/dev/stdout.lock': No such file or directory

The best I could come up with is creating a no checkout worktree for `my-branch` and using a FIFO for the index file, instead of a conventional file. The shell script equivalent of it would be as follows (I would be happy if you can point out any errors in this script as well):

	set -e
	
	git_dir=$(git rev-parse --git-dir)
	worktree_name=my-program
	worktree_location=$git_dir/$worktree_name
	
	# Ran only once
	function init_worktree {
		branch_name=my-branch
		worktree_gitdir=$git_dir/worktrees/$worktree_name
		
		git worktree add "$worktree_location" "$branch_name" --no-checkout
		rm -f "$worktree_gitdir/index”
		mkfifo "$worktree_gitdir/index”
		
		echo "Initialized worktree at $worktree_location”
	}

	# Ran on every commit
	function commit_worktree {
		cd "$worktree_location”
		git read-tree —empty
		git update-index --add \
		--cacheinfo "100644,0123456789abcdef0123456789abcdef01234567,path/to/first/file” \
		--cacheinfo "100755,123456789abcdef0123456789abcdef012345670,path/to/second/file” \
		--cacheinfo "100644,23456789abcdef0123456789abcdef0123456701,path/to/third/file”
		# etc. Will be received as arguments or from STDIN.
		git commit -m "Commit message”
	}

So I guess this is the best it gets? If I wanna make it better, I guess I will need to use libgit2?

Thank you