How to use `jq` to obtain the keys

Question

My json looks like this :

{   "20160522201409-jobsv1-1": {     "vmStateDisplayName": "Ready",     "servers": {       "20160522201409 jobs_v1 1": {         "serverStateDisplayName": "Ready",         "creationDate": "2016-05-22T20:14:22.000+0000",         "state": "READY",         "provisionStatus": "PENDING",         "serverRole": "ROLE",         "serverType": "SERVER",         "serverName": "20160522201409 jobs_v1 1",         "serverId": 2902       }     },     "isAdminNode": true,     "creationDate": "2016-05-22T20:14:23.000+0000",     "totalStorage": 15360,     "shapeId": "ot1",     "state": "READY",     "vmId": 4353,     "hostName": "20160522201409-jobsv1-1",     "label": "20160522201409 jobs_v1 ADMIN_SERVER 1",     "ipAddress": "10.252.159.39",     "publicIpAddress": "10.252.159.39",     "usageType": "ADMIN_SERVER",     "role": "ADMIN_SERVER",     "componentType": "jobs_v1"   } } 

My key keeps changing from time to time. So for example 20160522201409-jobsv1-1 may be something else tomorrow. Also I may more than one such entry in the json payload.

I want to echo $KEYS and I am trying to do it using jq.

Things I have tried : | jq .KEYS is the command i use frequently.

Is there a jq command to display all the primary keys in the json?

I only care about the hostname field. And I would like to extract that out. I know how to do it using grep but it is NOT a clean approach.

Answer 1

You can simply use: keys:

% jq 'keys' my.json [   "20160522201409-jobsv1-1" ] 

And to get the first:

% jq -r 'keys[0]' my.json 20160522201409-jobsv1-1 

-r is for raw output:

--raw-output / -r: With this option, if the filter’s result is a string then it will be written directly to standard output rather than being formatted as a JSON string with quotes. This can be useful for making jq filters talk to non-JSON-based systems.

Source

If you want a known value below an unknown property, eg xxx.hostName:

% jq -r '.[].hostName' my.json 20160522201409-jobsv1-1