[SOLVED] Convert json structure and conditional update values using environment variables with JQ

Convert json structure and conditional update values using environment variables with JQ

I have the following json:

{
  "Parameters": {
    "AmiId": "/my/image/id/latest",
    "InstanceType": "t3.medium",
    "Environment": "$ENV_DEFINITION"
  }
}

And I have exported the $ENV_DEFINITION with the value dev.

NOTE: I want to keep the literal value $ENV_DEFINTION if the environment variable is not set. That's why I'm using the // . part when accessing the env[] array in the command below.

I need to obtain the following output:

'AmiId=/my/image/id/latest' 'InstanceType=t3.medium' 'Environment=dev'

I'm able to get the above output witht he following jq command:

jq -r '[ .Parameters | to_entries[] | .value |= (env[.[1:]] // .) | [.key, .value] | join("=") ] | @sh' < myfile.json

But then I needed to add a few more parameters to json:

{
  "Parameters": {
    "AmiId": "/my/image/id/latest",
    "InstanceType": "t3.medium",
    "Environment": "$ENV_DEFINITION",
    "MinSize": 0,
    "MaxSize": 0,
    "DesiredCapacity": 0,
  }
}

And jq started to fail with the following message:

jq: error (at myfile:10): Cannot index number with object

Well, looks like it fails when the json values are integer as it cannont index integer values at the following place: env[.[1:]].

Then I came up with this new jq command:

jq -r '[ .Parameters | to_entries[] | select((.value|tostring)|startswith("$")) |= (env[.[1:]] // .) | [.key, .value] | join("=") ] | @sh' < myfile.json

But now, this fail when trying to replace the $ENV_DEFINITION. If I take it out of the json file, the above command works.

The error message is:

jq: error (at myfile.json:5): Cannot index object with object

I have tried the following

jq -r '[ .Parameters | to_entries[] | .value |= if ((.value|tostring)|startswith("$")) then (env[.[1:]] // .) else . end | [.key, .value] | join("=") ]' < myfile.json

But:

jq: error (at myfile.json:5): Cannot index string with string "value"

I'm still fighting with jq and it's documentation here to figure out what to do but any help will be welcome.

Solution

To only trigger the lookup if the value is a string, you can use select(type == "string"), which also has the strings shortcut. So, in your first attempt, just replace .[1:] with strings[1:], and you should be good to go.

jq -r '[ .Parameters | to_entries[] | .value |= (env[strings[1:]] // .) | [.key, .value] | join("=") ] | @sh' < myfile.json