3 approaches to time string parse and calculate

gistfile1.txt

# regexp parser and eval variant
str = "1 year 2 months 3 days 2 hours 3 minutes 59 seconds"
t = {'minute[s]?': '*60+', 'hour[s]?': '*60*60+', 'day[s]?': '*60*60*24+', 'second[s]?': '+0', 'month[s]?': '*30*60*60*24+', 'year[s]?': '*12*30*60*60*24+'}
s = t.each {|x,y| str.gsub!(Regexp.new(x.to_s), y)}
seconds = eval(str)

# hash parser and inject variant
SECOND = SECONDS = 1
MINUTE = MINUTES = 60
HOUR = HOURS = 3600
DAY = DAYS = 86400
WEEK = WEEKS = 604800
MONTH = MONTHS = 2419200
YEAR = YEARS = 29030400
def str_to_sec_with_const(str)
  Hash[*str.strip.split(" ")].invert.inject(0){|result,(k,v)| result + Object.const_get(k.upcase) * v.to_i}
end

# RoR variant
"1 year 2 second 3 hours 17 days".scan(/(\d+)\s+(\w+)/).map{ |m| m[0].to_i.send(m[1]) }.sum.seconds