Check certificate expiration

certcheck.rb

#!/usr/bin/env ruby

require 'date'
require 'time'

domain = ARGV[0]
if !domain
  STDERR.puts "no domain given"
  exit(-1)
end
dates = `openssl s_client -connect #{domain}:443 2>/dev/null </dev/null | openssl x509 -noout -dates`

dates = dates.split("\n").map(&:strip).map{|date| date.split("=")}.map{|key, date| [key, Time.parse(date)]}.to_h

def date_diff(d1, d2)
  (d1.to_date - d2.to_date).to_i
end

puts '=== SSL Cert Check ==='
puts "Domain: #{domain}"
days_used = date_diff(Date.today, dates['notBefore'])
days_left = date_diff(dates['notAfter'], Date.today)
duration = date_diff(dates['notAfter'], dates['notBefore'])
printf "#{days_used} of #{duration} days used (%.0f%%)\n", days_used.to_f/duration*100
puts "#{days_left} days left"