Script for creating a branch that combines multiple other branches

build-merge-branch.sh

#!/usr/bin/env bash

set -euo pipefail

destination_branch_name="${1:-merge-pile}"
branch_list="${2:-branch-list.txt}"

if [[ ! -f "${branch_list}" ]] ; then
  echo "ERROR: Branch list file (${branch_list}) doesn't exist" >&2
  exit 1
fi

# @see https://stackoverflow.com/a/30781568
if git merge HEAD &> /dev/null ; then
  git checkout master
  git fetch origin master
  git pull origin master \
    --ff

  # recreate branch from master
  git branch \
    --delete \
    --force \
    "${destination_branch_name}" \
    &>/dev/null \
    || true
  git checkout \
    -B \
    "${destination_branch_name}" \
    origin/master
  git checkout \
    "${destination_branch_name}"
else
  git merge \
    --continue
fi

while IFS= read -r branch ; do
  git merge \
    --ff \
    "${branch}"
done < "${branch_list}"

git branch \
  --unset-upstream \
  || true