split a git commit per file

git-split.sh

#!/bin/bash
# to split all commits since origin/master run:
# git rebase --interactive --exec git-split.sh origin/master

set -e

LF=$'\n'
SHA=$(git rev-parse --short HEAD)
MSG=$(git show -s --format=%B HEAD)
set -f; IFS=$'\n'
FILES=($(git diff-tree --no-commit-id --name-only -r HEAD))
set +f; unset IFS

git reset HEAD^

for f in "${FILES[@]}"; do
  git add "$f"
  git commit -m "$SHA $f$LF$LF$MSG"
done