utility to quickly dim or brighten all monitors on linux with xrandr

monitor_dim.rb

#!/usr/bin/env ruby
# frozen_string_literal: true

LOWEST=0.3
HIGHEST=4


def sys(cmd, *args, **kwargs)
  puts("*** running: \e[1m\e[33m#{cmd} #{args}\e[0m\e[22m")
  system(cmd, *args, exception: true, **kwargs)
  #return $?.exitstatus
  $?.success?
end


#  use Integer(str) and see if it raises:
def is_float?(str)
  !!Float(str)
rescue ArgumentError, TypeError
  false
end

def show_usage(error_msg)
  puts "\n***\n*** ERROR: #{error_msg}\n***"
  
  puts "*** brighteness of (#{ARGV[0]}) is not valid\n\n" unless ARGV.empty?

  exe_name = File.basename(__FILE__)
  
  puts "usage #{exe_name} (brightness)"
  puts "      (brightness) must be in range #{LOWEST} - #{HIGHEST}"
  puts ""
  puts "      for example: ruby #{exe_name} 1.2"
  exit 1;
end

def get_brightness
  show_usage('invalid argument: brightness must be a decimal number') unless is_float?(ARGV[0])
  brightness = ARGV[0].to_f
  show_usage("brightness out of allowed range [#{LOWEST} - #{HIGHEST}]") unless brightness.between?(LOWEST, HIGHEST)
  brightness
end

def set_monitor_brightness(brightness)
  puts "setting brightness to  #{brightness}"
  monitor_list = `xrandr -q | grep " connected" | cut -d ' ' -f 1`
  monitors = monitor_list.split("\n")
  puts "updating brightness for monitors: #{monitors}"
  monitors.each do |monitor|
    cmd="xrandr --output #{monitor} --brightness #{brightness}"
    sys(cmd)
  end
end

set_monitor_brightness(get_brightness)