Adventures in Ruby

I’m learning ruby. Finding time to work towards this goal is proving difficult but I’m forcing myself to use ruby wherever possible to aid in my learning. I’ll be putting some of my lame code on here to chronicle my learning and hopefully get some feedback on how I can improve things. I recently came across a good opportunity when I needed to generate a list of nodes to use with the puppet catalog preview tool

I wanted to get a full picture of my infrastructure and represent all our nodes in the report output without having to manually type a large node list. Puppet already has all my node names so I just need to extract them . My first step was to query the nodes endpoint in puppetdb for all nodes and pipe it into a file.

curl > nodesout.txt

The output of this is json with an array of hashes.

"name" : "",
"deactivated" : null,
"catalog_timestamp" : "2016-11-28T19:28:14.828Z",
"facts_timestamp" : "2016-11-28T19:28:12.112Z",
"report_timestamp" : "2016-11-28T19:28:13.443Z"
"name" : "",
"deactivated" : null,
"catalog_timestamp" : "2016-11-28T19:28:14.828Z",
"facts_timestamp" : "2016-11-28T19:28:12.112Z",
"report_timestamp" : "2016-11-28T19:28:13.443Z"

I only want the name of each node so I need to parse that out. It was a great opportunity to open pry and get some practice!

  • load json so I can parse the file
[1] pry(main)> require 'json'
=> true
  • read in the file
[2] pry(main)> file ='nodesout.txt')
  • parse the file into a variable
pry(main)> data_hash = JSON.parse(file)
=> [{"name"=>"",
[4] pry(main)> data_hash.class
=> Array
  • setup a method to iterate over the data and write each hostname to a new line in a file
[5] pry(main)> def list_nodes(input)
[5] pry(main)*'nodes_out.txt', 'a') do |f|
[5] pry(main)*     input.each do |i|
[5] pry(main)*       f.puts i["name"]
[5] pry(main)*     end
[5] pry(main)*   end
[5] pry(main)* end
=> :list_nodes
  • run the method against my data_hash
[6] pry(main)> list_nodes(data_hash)
[7] pry(main)> exit

I now have the list of nodes I was looking for!

$ cat nodes_out.txt

This accomplished what I needed and also saved me a lot of time (like putting the puppetdb query directly in the ruby stuff). I’m certain there may be a cleaner way to do this, but that’s what learning is for!

2 thoughts on “Adventures in Ruby

  1. Yay for Ruby! If you’re looking for a few nifty tricks, here’s something worth mentioning about the `JSON.parse` method: While `JSON.parse` is slightly more secure with untrusted sources, it will only take a String as input (like you provided via the contents of the `file` variable). `JSON.load` however, will take a String or anything that responds to `#read()`, which includes IO objects like the result of `‘nodesout.txt’)`. This can be combined with the `Kernel#open` method (after it is patched via the OpenURI standard library) to avoid the call to curl and the first file altogether. Check it out:

    require ‘json’
    require ‘open-uri’
    data_hash = JSON.load open(‘’)

    This leaves you with the same Array, but with less curl calls and files cluttering your filesystem. 🙂

    Liked by 1 person

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