Ruby wrapper for brightness CLI (https://github.com/nriley/brightness)

brightness.rb

#!/usr/bin/env ruby
# Brett Terpstra 2019
# This script adds the ability to increment/decrement display brightness
# levels to the nriley/brightness CLI (Copyright (c) 2014-2019, Nicholas Riley)
# Requires CLI installation: `brew install brightness`
# See https://github.com/nriley/brightness
CMD = "/usr/local/bin/brightness"

# Display usage and exit
def usage(code)
  puts "Usage: #{File.basename(__FILE__)} [+-=]X"
  puts "  [+-]X increment/decrement by integer 0-100"
  puts "  =X set brightness 0-100"
  Process.exit code
end

# Returns current brightness of the first display as a percentage
# (0-100). All displays will end up set to the same level, so we're only
# checking for the first display.
def get_brightness
  details = %x{#{CMD} -l}

  return (details.match(/display 0: brightness (\d\.\d+)/)[1].to_f.round(2) * 100).to_i
end

# Set brightness of all displays to a percentage (0-100)
def set_brightness(level)
  target = level * 0.01
  return system %Q{"#{CMD}" #{target} &> /dev/null}
end


def main(arg)
  # if the argument starts with =, set brightness
  if arg =~ /^=(\d{1,3})/
    target = $1.to_i

    if target < 0 || target > 100
      puts "Error: #{target} is out of range"
      usage(1)
    end

  # if argument is a positive or negative integer, increment or decrement
  # brightness
  else
    inc = arg.to_i
    current = get_brightness
    target = (current + inc)

    # ensure the adjusted level is in range. Don't throw an error, allow
    # overruns and just compensate
    if target > 100
      target = 100
    elsif target < 0
      target = 0
    end
  end

  # Execute CLI
  res = set_brightness(target)
  if res
    $stdout.print get_brightness
  else
    $stdout.puts "Error setting brightness"
    Process.exit 1
  end
end

# Ensure brightness CLI is installed
unless File.executable?(CMD)
  puts "Error: brightness executable missing"
  puts "Requires brightness CLI (brew install brightness)"
  Process.exit 1
end

# Ensure the argument is valid
if ARGV.length != 1 || ARGV[0] !~ /^[+-=]?\d{1,3}$/
  usage(1)
else
  main(ARGV[0])
end