List all Memcached keys using Ruby (inspired by https://gist.github.com/bkimble/1365005/b0a4566f3abdd43dad79bec6542929bf927a0ab3)

keys.rb

require "net/telnet"

def keys(hosts, pattern = nil)
  [hosts].flatten.each do |host|
    slabs = {}

    telnet = Net::Telnet::new("Host" => host, "Port" => 11211, "Timeout" => 3)
    telnet.cmd("String" => "stats items", "Match" => /^END/) do |stats|
      slabs = Hash[stats.scan(/STAT items:(\d+):number (\d+)/)]
    end

    puts "HOST: #{host}"

    slabs.each do |(id, count)|
      puts "SLAB: #{id} (#{count})"
      telnet.cmd("String" => "stats cachedump #{id} #{count}", "Match" => /^END/) do |stats|
        stats.scan(/^ITEM (.+?) \[(\d+) b; (\d+) s\]$/).each do |item|
          key, bytes, expires_time = item
          puts key if pattern.nil? || key.match(pattern)
        end
      end
    end

    telnet.close
  end
  nil
end

keys "<your memcached host or hosts>", "<your optional filter pattern>"