Script for changing monitor brightness on Linux. Could be mapped to the XF86MonBrightnessUp and XF86MonBrightnessDown keys.

screen_brightness.sh

#!/usr/bin/env bash

# Changes the monitor brightness.
# Usage examples: "screen_brightness.sh +500", "screen_brightness 3000"

if (( $# >= 1 )); then
  argument="$1"

  # Writing to this file changes the monitor brightness.
  # The parentheses are used to have a wildcard for the
  # directory containing the brightness file. The directory
  # could be "intel_backlight" or "acpi_video0", for example
  brightness_file=(/sys/class/backlight/*/brightness)

  if [[ $argument = +* ]]; then
    amount=${argument#*+}
    current_brightness=$(cat "${brightness_file}")
    new_brightness=$((current_brightness + amount))
    echo $new_brightness > "${brightness_file}"

  elif [[ $argument = -* ]]; then
    amount=${argument#*-}
    current_brightness=$(cat "${brightness_file}")
    new_brightness=$((current_brightness - amount))
    echo $new_brightness > "${brightness_file}"
  else
    # If the argument is something else than an integer, this will
    # yield "write error: Invalid argument"
    echo "${argument}" > "${brightness_file}"
  fi

else
  echo "Please pass a single argument. Usage examples: \"screen_brightness.sh +500\", \"screen_brightness 3000\""
fi