Do this:

export KUBECONFIG=~/.kube/config:~/someotherconfig 
kubectl config view --flatten

You can then pipe that out to a new file if needed.

If you find doing this a lot.. There is now also the 'krew' plugin package manager for kubectl. And there is a plugin for managing your ./kube/config file.

Using the 'konfig' plugin the syntax will be:

kubectl konfig import -s new.yaml

To install krew: https://github.com/kubernetes-sigs/krew

Using multiple kubeconfigs at once

Sometimes you have a bunch of small kubeconfig files (e.g. one per cluster) but you want to use them all at once, with tools like kubectl or kubectx that work with multiple contexts at once.

To do that, you need a “merged” kubeconfig file. In the section "Merging kubeconfig files" below, we explain how you can merge the kubeconfigs into a single file, but you can also merge them in-memory.

By specifying multiple files in KUBECONFIG environment variable, you can temporarily stitch kubeconfig files together and use them all in kubectl .

#
# Kubeconfig in-memory merge
#
export KUBECONFIG=file1:file2
kubectl get pods --context=cluster-1
kubectl get pods --context=cluster-2

#
# For your example
# merging your kubeconfig file w/ $HOME/.kube/config (w/ cp backup)
#
cp $HOME/.kube/config $HOME/.kube/config.backup.$(date +%Y-%m-%d.%H:%M:%S)
KUBECONFIG= $HOME/.kube/config:file2: kubectl config view --merge --flatten > \
~/.kube/merged_kubeconfig && mv ~/.kube/merged_kubeconfig ~/.kube/config
kubectl get pods --context=cluster-1
kubectl get pods --context=cluster-2

Merging kubeconfig files

Since kubeconfig files are structured YAML files, you can’t just append them to get one big kubeconfig file, but kubectl can help you merge these files:

#
# Merging your kubeconfig file w/ $HOME/.kube/config (w/ cp backup)
#
cp $HOME/.kube/config $HOME/.kube/config.backup.$(date +%Y-%m-%d.%H:%M:%S)
KUBECONFIG=$HOME/.kube/config:file2:file3 kubectl config view --merge --flatten > \
~/.kube/merged_kubeconfig && mv ~/.kube/merged_kubeconfig ~/.kube/config
kubectl get pods --context=cluster-1
kubectl get pods --context=cluster-2

Extracting a context from a kubeconfig file

Let’s say you followed the before merging kubeconfig files and have a merged kubeconfig file in $HOME/.kube/config. Now you want to extract a cluster’s information to a portable kubeconfig file that only has the parts you need to connect to that cluster.

Run:

KUBECONFIG=$HOME/.kube/config kubectl config view \
    --minify --flatten --context=context-1 > $HOME/.kube/config-context-1

#
# using --kubeconfig flag
#
kubectl get pods --kubeconfig=$HOME/.kube/config-context-1

#
# or 
# using `KUBECONFIG` environment variable
#
KUBECONFIG=$HOME/.kube/config-context-1 kubectl get pods

#
# or 
# keep using kubeconfig file at $HOME/.kube/config (which has the merged context)
#
kubectl get pods --context=cluster-1

In this command, we extract data about context-1 from $HOME/.kube/config to config-context-1 file. The --minify flag allows us to extract only info about that context, and the --flatten flag allows us to keep the credentials unredacted.

ref article: https://ahmet.im/blog/mastering-kubeconfig/

If you want to merge two config files in a single one

I found this way (not sure if this is the simplest)

# Add the two config files to the env var
export KUBECONFIG=~/.kube/config:~/Desktop/configFile2.yaml

# Review that you have two configurations in one view
kubectl config view

# View the raw config and output to a new file
kubectl config view --raw > /tmp/config

Then copy the new config file where you want, also do not forget to unset KUBECONFIG the env variable