Teaches migration of git repo from one url to another + git submodule

migrate_git_submodule

### To simply clone as git submodule do:

git submodule add <clone_repo_url>
git commit -am "new submodule added"

### To migrate git repo into submodule

git clone <old_repo_url>
git remote add <new_repo_name> <new_repo_url>
git push <new_repo_name> master
git remote rm origin
<edit .git/config to replace "new_repo_name" to "origin">
git push new_repo_name master
<edit .git/config to add branch "master" three lines>
[branch "master"]
        remote = origin
        merge = refs/heads/master

git clone <top_repo_url>
git submodule add <new_repo_url>
git commit -am "adding new_repo as submodule"
git push origin master

git clone <top_repo_url>
git submodule init
git submodule update

git pull --recurse-submodules

# The submodule init + update can be done with:

git submodule update --init

# The recurse submodules above makes all submodules HEAD detached, fix it by:

git submodule foreach -q --recursive 'git checkout $(git config -f $toplevel/.gitmodules submodule.$name.branch || echo master)'

# Display status of submodules when doing git status:

git config --global status.submoduleSummary true

# Scripting for pulling the main repo and updating submodules automatically:

#!/usr/bin/env bash

git pull "$@" &&
  git submodule sync --recursive &&
  git submodule update --init --recursive