Managing contents of another "sub" repo inside a "main" repo using `git subtree`

.gitignore

/main
/sub
/.main
/.sub

test.sh

#!/bin/sh
set -e

DIR=$PWD

commits() {
  repo=$1
  shift
  for f in $@; do
    touch $f
    git add $f
    git commit -m "added $f for $repo"
  done
  git push -u origin master
}

show() {
  ls -R
  read -p "show: Press Return." anything
}

sync() {
  cd main
  git subtree pull --prefix sub sub master -m "Merging from sub"
  git subtree push --prefix sub sub master -m "Merging to sub"
  cd ..
  #read -p "sync: Press Return." anything
}

# Init two repositories "main" and "sub", add a corresponding --bare repository
# as origin
for r in main sub; do
  rm -rf $r .$r
  git init --bare .$r
  git init $r
  cd $r
  git remote add origin $DIR/.$r
  cd ..
done

# Populate with some independent commits
cd main
commits main a b c
cd ..
cd sub
commits sub d e f
cd ..

# Add "sub" repository as subdir to "main" repository
cd main
git remote add sub $DIR/.sub
git fetch --all
git branch sub sub/master
git subtree add --prefix sub sub
git subtree pull --prefix sub sub master
git subtree push --prefix sub sub master
git push
cd ..

show

# Add somme commits to "sub", push
cd sub
commits sub g h i
cd ..

# Pull the newly added commits into "main/sub"
sync
show

# Add somme commits to "main/sub", push
cd main/sub
commits main/sub j k l
cd ../..

# Push the newly added commits to "sub"
sync
cd sub
git pull
cd ..

show