add_timestamp.rb

#!/usr/bin/env ruby
# frozen_string_literal: true

ARGV.each do |original_file|
  unless File.exist? original_file
    puts "#{original_file} does not exist"
    next
  end

  timestamp = Time.now.utc.strftime("%Y%m%d%s")
  file_parts = original_file.match(/(.*)\.(png|jpg)/)
  new_file = "#{file_parts[1]}-#{timestamp}.#{file_parts[2]}"

  puts "Changing #{original_file} to #{new_file}"
  `mv #{original_file} #{new_file}`
end