How to specify a filter for Kubectl -o flag=custom-column

Question

I want to use kubectl get -o=custom-columns to extract information with specific columns. The cropped yaml response is like this

{
    "apiVersion": "v1",
    "items": [
        {
            "apiVersion": "v1",
            "kind": "Pod",
            "metadata": {
                "creationTimestamp": "2018-11-27T14:37:46Z",
                "generateName": "kubernetes-bootcamp-5c69669756-",
                "labels": {
                    "pod-template-hash": "1725225312",
                    "run": "kubernetes-bootcamp"
                },
                "name": "kubernetes-bootcamp-5c69669756-cxhwf",
                "namespace": "default",
                "ownerReferences": [
                    {
                        "apiVersion": "extensions/v1beta1",
                        "blockOwnerDeletion": true,
                        "controller": true,
                        "kind": "ReplicaSet",
                        "name": "kubernetes-bootcamp-5c69669756",
                        "uid": "950aac8e-f24f-11e8-bf5d-065b6ba59aa8"
                    }
                ],
                "resourceVersion": "118035",
                "selfLink": "/api/v1/namespaces/default/pods/kubernetes-bootcamp-5c69669756-cxhwf",
                "uid": "0190c234-f252-11e8-bf5d-065b6ba59aa8"
            },

I want to extract the name from items[0].metadata.name, but I don't know the syntax.

My questions:

1. What is the query syntax used in this situation. Is it JSON path? I don't see it documented.
2. What is the specific query in my case?

Answer 1

Since the result is JSON, pipe the result to jq and go from there.

kubectl get | jq '.items[0].metadata.name'

yields

➜ cat abc.json | jq '.items[0].metadata.name'
"kubernetes-bootcamp-5c69669756-cxhwf"

Answer 2

The syntax of the command is as follows;

$ kubectl get pods <optional_pod_name> --output custom-columns="NAME:.metadata.name"
NAME
kubernetes-bootcamp-5c69669756-cxhwf

You can add more columns by separating them with commas. For example;

$ kubectl get pods <optional_pod_name> -o custom-columns="NAME:.metadata.name,STATUS:.status.phase"

NAME                                   STATUS
kubernetes-bootcamp-5c69669756-cxhwf   Running

Answer 3

You can also use JSONPath:

kubectl get nodes --output=custom-columns='$COLUMN_NAME:$JSON_PATH'
kubectl get nodes --output=custom-columns='NAME:{.metadata.name}' # optional curly bracket
kubectl get nodes --output=custom-columns='NAME:.metadata.name,POD_CIDR:{.spec.podCIDR}'
kubectl get nodes --output=jsonpath='{range .items[*]}{.metadata.name}{" "}{.spec.podCIDR}{"\n"}{end}'