$ characters get removed from json - ruby

Question

I am currently improving the deployment process of our service.
In particular, I want to update the revision stored in the opsworks CustomJson stack property as soon as we have deployed a new one.
For this I created a new task in our rakefile. Here is the code:
desc "update revision in custom json of stack"
task :update_stack_revision, [:revision, :stack_id] do |t, arg|
revision = arg[:revision]
stack_id = arg[:stack_id]
# get stack config
stack_description = `aws opsworks \
--region us-east-1 \
describe-stacks \
--stack-id #{stack_id}`
# get the json config
raw_custom_json = JSON.parse(stack_description)["Stacks"][0]["CustomJson"]
# make it parseable by removing invalid chararcters
raw_custom_json = raw_custom_json.gsub(/(\\n)/, '')
raw_custom_json = raw_custom_json.gsub(/(\\")/, '"')
# parse json and update revision
parsed_custom_json = JSON.parse(raw_custom_json)
parsed_custom_json["git"]["revision"] = revision
# transform updated object back into json and bring it into a format required by aws opsworks
updated_json = JSON.generate(parsed_custom_json)
updated_json = updated_json.gsub('"', '\"')
# send update
`aws opsworks \
--region us-east-1 \
update-stack \
--stack-id #{stack_id} \
--custom-json "#{updated_json}"`
end
During this process $ characters are lost for some reason.
I tried reproducing this error by executing each command individually. Apparently the last one - aws opsworks update-stack - is at fault here. I'd really like to know why and how to stop this.