if where git &>/dev/null; then
  function prompt-git-branch() {
    local branch_name

      # TODO: show proper name if some heads point the same branch.
    branch_name="$(git name-rev --name-only HEAD 2>/dev/null)"
    if [ $? = 0 ]; then
      echo " [$branch_name]"
      return 0
    else
      return 1
    fi
  }
else
  function prompt-git-branch() {
    echo ''
  }
fi