power.rb

#!/usr/bin/env ruby

def output_nicely(title, value)
  puts format('%-25s %6.2f', "#{title}:", value)
end

data = `/usr/sbin/system_profiler SPPowerDataType`

remaining = data[/Charge Remaining.*: (\d+)/, 1].to_f
capacity  = data[/Full Charge Capacity.*: (\d+)/, 1].to_f
amperage = data[/Amperage.*: (\d+)/, 1].to_f
voltage = data[/Voltage.*: (\d+)/, 1].to_f
calc_power = amperage * voltage / 1000000
calc_percent = remaining / capacity
calc_remaining_hours = remaining / amperage

output_nicely 'Remaining (%)',           (calc_percent * 100)
output_nicely 'Current Power Draw (W)', (calc_power)
output_nicely 'Remaining Time (H)',     (calc_remaining_hours)