Use kubectl to get all running images in a Kubernetes cluster.

kubectl_get_images.sh

#! /bin/sh
set -Eeou pipefail

# kubectl_get_images.sh
# 
# Use kubectl to get all running images in a Kubernetes cluster.
# Ref: https://kubernetes.io/docs/tasks/access-application-cluster/list-all-running-container-images/

# if context is provided, switch context
if [[ ! -z ${1:-} ]]; then
  kubectl config use-context $1
fi

# build images list
IMAGES=
while read IMAGE_TAG; do
  IMAGE="${IMAGE_TAG%%:*}"
  # prefix docker.io images for clarity  
  if [[ $IMAGE =~ ^[^\.\/]+(\/|$) ]]; then
    IMAGE="docker.io/$IMAGE"
  fi
  IMAGES="$IMAGES\n$IMAGE"
done <<< "$(kubectl get pods --all-namespaces -o jsonpath="{.items[*].spec['initContainers', 'containers'][*].image}" | tr -s '[[:space:]]' '\n')"

# echo images sorted and de-duped
echo $IMAGES | sort -u