Can I merge/sync a sub-folder from one branch to the root of another in git?

Question

I want to have a /doc folder in master and easily merge/sync it to the root of a gh-pages branch. What is the easiest way to do this?

Answer 1

One nice trick would be to declare the branch gh-branch as a submodule in your master branch (also more detailed in "How to add a git repo as a submodule of itself?").

That way, when you are in your master branch, you see a folder gh-branch which represents the gh-branch content.

You could then:

• version doc only in the gh-branch
• have a symlink doc in your master branch, linked to gh-branch/doc

That way, you maintain the doc/ content only in one place.

Answer 2

#!/bin/sh

# if there's a docbranch tree and it matches master:doc,
# then get out now, there's nothing to do:

current=`git rev-parse -q --verify docbranch:` \
&& test $current = "`git rev-parse -q --verify master:doc`" \
&& exit 0

# update the docbranch ref to a new commit ...    
git update-ref refs/heads/docbranch $(
        # ... which has master:doc, parented on docbranch if that exists yet
        git commit-tree ${current:+-p docbranch} -m "updating" master:doc
)

You can use that as your post-commit hook and chmod +x it, every time you commit anything, if the master doc directory has changed it will commit it to the head of docbranch.

Since the tree's already committed, the only thing this adds is the (~200 byte) commit object itself.