Use git filter-branch to move all projects files to a subdir and rewrite all commits

git-filter-branch-move-files.md

1. Clone project

2. Checkout all branches that contain the files that should be moved

3. Delete the remote

4. Run the filter-branch command:

   git filter-branch --tree-filter 'mkdir -p /path/to/tmp; mv * /path/to/tmp; mkdir subdir; mv /path/to/tmp/* subdir/' --tag-name-filter cat --prune-empty -- --all

   • All files are first copied to a temporary dir and move from there to the new destination
   • Existing tags are updated
   • Empty commits are ignored
   • The filters are applied to all branches

5. Add the remote

6. Push (force) all branches and tags back to remote:

   git push -f --all
   git push -f --tags

Really helpful although I forgot to move something trivial so deleted then added in afterwards:
git filter-branch --tree-filter 'rm -f .gitignore' HEAD

This doesn't move hidden content (files or directories starting with ".") to the subdirectory.

@rosasurfer I found find utility to be helpful (3 levels of nested quotes is a little confusing, though).

git filter-branch --tree-filter 'mkdir subdir; find . -maxdepth 1 -not -name .git -not -name subdir -exec sh -c ''mv "$@" subdir'' {} +' --tag-name-filter cat --prune-empty -- --all