battery-status.rb

#!/usr/bin/env ruby
require 'optparse'

class Battery
  DEFAULT_FORMAT = "P (S: R)"

  def self.status
    _, percent, status, remaining, _ = %x{pmset -g batt|grep InternalBattery}.split(/\t|;/).map(&:strip)
    percent.gsub!(/%/, '')
    remaining.gsub!(/[\(\)]/, '')
    remaining.gsub!(/\s*remaining/, '')

    new(percent, status, remaining)
  end

  attr_reader :percent, :status, :remaining

  def initialize(percent, status, remaining)
    @percent, @status, @remaining = percent, status, remaining
  end

  def charging?
    status != 'discharging'
  end

  def to_s(format = nil)
    format ||= DEFAULT_FORMAT
    format
      .gsub(/P/, percent)
      .gsub(/R/, remaining)
      .gsub(/S/, status)
  end
end

options = {
  discharging: false
}

OptionParser.new do |opts|
  opts.banner = "Usage: #{$0} [options]"

  opts.on("-d", "Only show when discharging") do |d|
    options[:discharging] = true
  end
end.parse!

battery = Battery.status

if options[:discharging]
  if battery.charging?
    exit 0
  end
end

print battery.to_s(ARGV[0])