Parse JSON file in ruby script and store specific value

Question

Parse the JSON file in Ruby script and obtain value for "key"

My JSON file looks like

"terraform": [
    {
  "backend": [
    {
      "s3": [
        {
          "bucket": "terraform-dev",
          "dynamodb": "terraform_files",
          "encrypt": "true",
          "key": "Apple/Employee/Background/terraform.tfstate"
        }
      ]
     }
  ],
  "required_version": "~> 0.11.8"
}
]

I tried writing this script in Ruby

#!/usr/bin/env ruby
require "json"
file = File.open "/Users/Test/conf.json"
data = JSON.load file
mykey= data['terraform'].first['backend']['s3']['key']
print mykey
file.close

Expected result: Apple/Employee/Background/terraform.tfstate

Error Message: no implicit conversion of String into Integer (TypeError)

Lakshmi Swetha G · Accepted Answer · 2019-06-10 21:13:52Z

1

Due to the structure of the conf.json where it has a composition of {} with a [], accessing every key by its name is difficult. So use mykey = data['terraform'][0]['backend'][0]['s3'][0]['key']

Here, terraform is a single object in {} which can be accessed by its name. It contains an array object [] which have to be accessed by index [0], since there is only one element. The same follows for the inner elements also. '{ } ' used for key-value pair Object and '[]' is used for Arrays with values in json.

and enclose the whole "terraform" in {} in conf.json.

answered Jun 10, 2019 at 21:13

Lakshmi Swetha G

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Sebastián Palma · Accepted Answer · 2019-06-10 21:21:46Z

1

Hash#dig works for accessing arrays based in their index:

p hash.dig(:terraform, 0, :backend, 0, :s3, 0, :key)
# "Apple/Employee/Background/terraform.tfstate"

The plus is it returns nil if some intermediate step is nil:

p foo.dig(:terraform, 0, :backend, 0, :s3, 1, :key) # nil
p foo.dig(:terraform, 0, :backend, 0, :orale, 0, :key) # nil

answered Jun 10, 2019 at 21:21

Sebastián Palma

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2 Comments

Jay Dorsey Over a year ago

I did not know that you could dig by index, so even though this didn't explain that the data structure was being accessed incorrectly, this is a valuable answer. Thank you for sharing this

Sebastián Palma Over a year ago

Yes, that's in the docs g = { foo: [10, 11, 12] }; g.dig(:foo, 1) #=> 11. And yes, I didn't point that out, thanks!

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