ref. http://moznion.hatenadiary.com/entry/2015/03/20/175035

git-export-branch

#!/bin/bash

set -e

repository_name() {
  basename "$(git rev-parse --show-toplevel)"
}

export_branch() {
  branch_name="$1"
  git archive \
    --format=tar \
    --prefix "$(repository_name)-${branch_name}/" \
    ${branch_name} \
    | tar -C . -xf -
}

export_all_branch() {
  branches=($(git for-each-ref --format='%(refname:short)' -- refs/heads))
  for b in "${branches[@]}"; do
    export_branch $b
  done
}

while getopts a opt ; do
  case "$opt" in
    a)
      export_all_branch $@
      ;;
    *)
      export_branch $@
      ;;
  esac
done