#!/bin/bash

mod_bl () {
  # Customizable configuration constants
  local -r DEFAULT_PRE=' '
  local -r DEFAULT_SUF='%'

  local -r pre="${1-${DEFAULT_PRE}}"
  local -r suf="${2-${DEFAULT_SUF}}"

  local bl_file bl max_bl_file max_bl

  bl_file="$(find /sys/class/backlight/*/brightness | head -n 1)"
  max_bl_file="$(dirname "${bl_file}")/max_brightness"
  read -r bl < "${bl_file}"
  read -r max_bl < "${max_bl_file}"
  # Use printf to do floating point arithmetic
  printf '%b%3.0f%b' "${pre}" "$((bl * 1000 / max_bl))e-1" "${suf}"
}