Question

I am working on replacing environment variables with values in Ruby, and I’m trying to figure out the best way to do this. I have a JSON feed that I am parsing, which looks like this: %MY_SERVER/json/data/mydata?someparameter and another that looks like %MY_OTHER_SERVER/json/data/mydata?somethingdifferent=thisorthat

Each of the servers has a different URL that needs to be input. I have looked around and have seen things talking about using replace or looking for a specific pattern, but I don’t think that is the most effective way.

Can anyone point me in the right direction, or offer some advice on the best way to accomplish my task?

Answer 1

Here’s the dynamic approach you seek:

urls = [
  '%MY_SERVER/json/data/mydata?someparameter',
  '%MY_OTHER_SERVER/json/data/mydata?somethingdifferent=thisorthat'
  ]

name_regex = /(%\w+)/

ENV['%MY_SERVER'] = 'http://google.com'

replaced = urls.map do |s|
  s.gsub name_regex do |env_name|
    if ENV[env_name]
      ENV[env_name] # replace
    else
      env_name # leave it untouched
    end

    # or, the same thing, but shorter
    # ENV[env_name] || env_name
  end
end

puts replaced
# >> http://google.com/json/data/mydata?someparameter
# >> %MY_OTHER_SERVER/json/data/mydata?somethingdifferent=thisorthat

You just need to scan your input string and find all things that look like a placeholder. Luckily, your strings have them clearly formatted. Then you just supply values in your ENV. If a value for placeholder is missing, it won’t be replaced.