How can I get the names of all namespaces containing the word "nginx" and store those names in an array

Question

Basically I want to automate this task where I have some namespaces in Kubernetes I need to delete and others that I want to leave alone. These namespaces contain the word nginx. So I was thinking in order to do that I could get the output of get namespace using some regex and store those namespaces in an array, then iterate through that array deleting them one by one.

array=($(kubectl get ns | jq -r 'keys[]'))
declare -p array
for n in {array};
do
    kubectl delete $n
done

I tried doing something like this but this is very basic and doesn't even have the regex. But I just left it here as an example to show what I'm trying to achieve. Any help is appreciated and thanks in advance.

Answer 1

kubectl get ns doesn't output JSON unless you add -o json. This:

array=($(kubectl get ns | jq -r 'keys[]'))

Should result in an error like:

parse error: Invalid numeric literal at line 1, column 5

---

kubectl get ns -o json emits a JSON response that contains a list of Namespace resources in the items key. You need to get the metadata.name attribute from each item, so:

kubectl get ns -o json | jq -r  '.items[].metadata.name'

---

You only want namespaces that contain the word "nginx". We could filter the above list with grep, or we could add that condition to our jq expression:

kubectl get ns -o json | jq -r  '.items[]|select(.metadata.name|test("nginx"))|.metadata.name'

This will output your desired namespaces. At this point, there's no reason to store this in array and use a for loop; you can just pipe the output to xargs:

kubectl get ns -o json |
jq -r  '.items[]|select(.metadata.name|test("nginx"))|.metadata.name' |
xargs kubectl delete ns

Answer 2

kubectl get ns 

output

NAME                          STATUS        AGE
default                       Active        75d
kube-public                   Active        75d
kube-system                   Active        75d
oci-service-operator-system   Active        31d
olm                           Active        31d

command

kubectl get ns --no-headers |  awk '{if ($1 ~ "de") print $1}'

Output

default
kube-node-lease

this will give you a list of namespaces

array=$(kubectl get ns --no-headers |  awk '{if ($1 ~ "de") print $1}')

Testing

bash-4.2$ array=$(kubectl get ns --no-headers |  awk '{if ($1 ~ "de") print $1}')
bash-4.2$ echo $array
default kube-node-lease
bash-4.2$ for n in $array; do echo $n; done
default
kube-node-lease
bash-4.2$