Bash function to tell if a path is writeable by current user

is_writeable.sh

_is_writeable() {
  if [[ "$(uname)" == "Darwin" ]]; then
    mapfile -d $' ' -t stat < <(stat -L -f '%p %g %u' "${1}")
  else
    mapfile -d $' ' -t stat < <(stat -L -c '%a %g %u' "${1}")
  fi

  declare -i prm=${stat[0]}
  declare -i grp=${stat[1]}
  declare -i own=${stat[2]}

  mapfile -t prm_words < <(echo "${prm}" | fold -w1)
  declare -i prm_other=${prm_words[-1]}
  declare -i prm_group=${prm_words[-2]}
  declare -i prm_owner=${prm_words[-3]}

  # Is writeable by others
  if (( prm_other & 1<<1 )); then
    return 0

  # Is writeable by group
  elif (( prm_group & 1<<1 )); then
    mapfile -t groups < <(id -G)

    for g in "${groups[@]}"; do
      if (( g == grp )); then
        return 0;
      fi
    done

  # Is writeable by owner
  elif (( prm_owner & 1<<1 )); then
    declare -i user
    user=$(id -u)
    if [[ "${user}" == "${own}" ]]; then
      return 0;
    fi
  fi

  return 1
}