Jenkins build failed because of an no value to a variable - jenkins

Question

I have a Jenkins file as like below:
stage("Deploy artifact for k8s sync")
{
sh '''
ns_exists=`kubectl get ns | grep ${target_cluster}`
if [ -z "$ns_exists" ]
then
echo "No namespace ${consider_namespace} exists in the cluster ${target_cluster}"
echo "Creating namespace ${consider_namespace} in the cluster ${target_cluster}"
kubectl apply "some yaml file"
else
if [ "${consider_kinds}" = "all" ] || [ "${consider_kinds}" = "serviceaccounts" ]
then
echo "Applying source serviceaccounts on target cluster ${target_cluster}"
kubectl "some yaml file"
fi
if [ "${consider_kinds}" = "all" ] || [ "${consider_kinds}" = "secrets" ]
then
echo "Applying source secrets on target cluster ${target_cluster}"
kubectl "some yaml file"
fi
if [ "${consider_kinds}" = "all" ] || [ "${consider_kinds}" = "configmaps" ]
then
echo "Applying source configmaps on target cluster ${target_cluster}"
kubectl apply -f ${BUILD_NUMBER}-${source_cluster}-${consider_namespace}-configmaps.yaml
fi
However, when I run, it fails with the error like below:
[Pipeline] }
[Pipeline] // stage
[Pipeline] stage
[Pipeline] { (Deploy artefact for k8s sync) (hide)
[Pipeline] sh
+ kubectl get ns
+ grep test-central-eks
+ ns_exists=
[Pipeline] }
[Pipeline] // stage
[Pipeline] }
[Pipeline] // node
[Pipeline] End of Pipeline
ERROR: script returned exit code 1
Finished: FAILURE
Wondering how to resolve it and why it should fail in first place?

Answer 1

As far as I can see you have a couple of things that make this to fail.
From your pipeline extract I can see that you are using variables that are not defined in the script, so I guess those are somehow environment variables or coming from previous step. In order to be able to use it, you will need string interpolation, in your case, a triple double quote https://groovy-lang.org/syntax.html#_triple_double_quoted_string
stage("Deploy artifact for k8s sync")
{
sh """
In the other hand, grep exit code is 1 when there is not match, in case you need to continue in the case that there is not match you can put a block command with a true condition
ns_exists=`kubectl get ns | {grep ${target_cluster} || true; }`
Finally, a good way to catch this problems is to replay the pipeline with debug in the shell blocks by adding set -x at the beginning of the sh sh block.
Please note as well that stderr is not printed, in case you need it you would need to redirect to the stdout and readed from returnStdout: true option of jenkins sh or a custom file where the stdout is redirected