Git subtree push --rejoin for all branches that changed a directory, using git merge-base.

migrate_branches.sh

#!/usr/bin/env bash
set -e
set -u

# Exit program with error message.
die() {
	echo -e "ERROR: $1"
	exit $2
}

# $1 = branch name
ignore_branch() {
	local branch branches=("HEAD" "develop" "master")
	local pattern="release"

	[[ "$1" == "$pattern"* ]] && return 0;
	for branch in "${branches[@]}"; do
		[[ "$1" == "$branch" ]] && return 0;
	done
	return 1
}

# $1 = remote name, $2 = branch name
modified_prefix() {
	local prefix='Web' master="$1/develop"
	local base="$(git merge-base ${1}/${2} "${master}")"
	local diff="$(git diff --stat ${1}/${2}..${base} -- "$prefix")"

	if [ -z "$diff" ]; then
		return 0
	fi
	return 1
}

# $1 = remote name, $2 = branch name
checkout_branch() {
	echo -n ":: Branch: ${1}/${2}"
	if git show-ref --verify --quiet "refs/heads/${2}"; then
		echo ' (checking out local branch...)'
		git checkout "${2}"
		git merge --ff-only "${1}/${2}" \
			|| die "Diverged local branch (${2}), synchronize with ${1} first." 2
	else
		echo ' (creating new branch...)'
		git checkout -b "${2}" "${1}/${2}"
	fi
}

# Main procedure.
main () {
	local remote='origin'
	local refs="refs/remotes/$remote"
	local branch branches=()

	eval "$(git for-each-ref --format='branches+=(%(refname))' "$refs" \
		| sed "s/refs\/remotes\/$remote\///g")"

	# Iterate through all branches in specific ref prefix
	for branch in "${branches[@]}"; do

		# Ignore certain branches, certainly those who didn't change prefix.
		if ignore_branch "$branch" || modified_prefix "$remote" "$branch"; then
			continue
		fi

		checkout_branch "$remote" "$branch"

		git log --decorate --oneline --graph -1

		echo ':: Performing subtree push'
		git subtree push --prefix Web webapp "$branch" --rejoin

		echo ":: Finished branch \`$branch\` successfully, hooray!"
		echo
	done
}
main