md5 Hash in a puppet custom function

Question

Currently I want to create an md5 hash from an argument. Then I want to write the hash into a file (the path is another argument).

That is the custom function:

   module Puppet::Parser::Functions
      newfunction(:write_line_to_file) do |args|
    require 'md5'
        filename = args[0]

        str = MD5.new(lookupvar(args[1])).to_s
        File.open(filename, 'a') {|fd| fd.puts str }
      end
    end

And the call in the puppet manifest:

write_line_to_file('/tmp/some_hash', "Hello world!")

The result I get is a file and the content is not the hash but the original string. (In the example Hello World!)

I know that this custom function has no practical use. I just want to understand how the md5 hash works.

---UPD---

new Function (it works properly):

   require 'digest'
   module Puppet::Parser::Functions
      newfunction(:lxwrite_line_to_file) do |args|
        filename = args[0]

        str = Digest::MD5.hexdigest args[1]
        File.open(filename, 'w') {|fd| fd.puts str }
      end
    end

Answer 1

Which ruby you are using?

In Ruby 2.0+ there is a Digest module (documentation here) - why you don't use it instead?.

You can use any hash, available in Digest, like this:

Digest::MD5.digest '123'
=> " ,\xB9b\xACY\a[\x96K\a\x15-#Kp"

or use hexdigest if you prefer hex representation

Digest::MD5.hexdigest '123'
=> "202cb962ac59075b964b07152d234b70"

There are also other hash-functions available there:

Digest::SHA2.hexdigest '123'
=> "a665a45920422f9d417e4867efdc4fb8a04a1f3fff1fa07e998e86f7f7a27ae3"