Rewrite git history by removing everything except desired files, which are represented by a line-separated list of regex patterns in ~/file_patterns.

git_filter_files

git filter-branch --tree-filter \
  'find . \
  \( -name ".gitignore" -o -path "./.git*" \) -prune -o \
  \( -type f -o -type l \) -exec echo \"{}\" ";" \
  | grep -vE -f ~/file_patterns \
  | xargs rm \
  && find . -empty -delete' \
  --prune-empty HEAD
  
# 1: rewrite git history by running the following command for each commit
# --- Command Start ---
# 2: breadth-first traversal of current directory
# 3: ignore (prune) `.gitignore` file and `.git` folder
# 4: echo any files or links surrounded by quotes (to prevent grep from getting tripped up by paths w/ spaces)
# 5: filter out the paths echoed by `find` which match the patterns in "~/file_patterns"
# 6: split outputs of `grep` to multiple calls of `rm` (delete the all files but those that match a line in "~/file_patterns")
# 7: find and delete any directories that are now empty
# --- Command End ---
# 8: prune any empty commits and run on the branch HEAD