Jenkins - Assign variable inside sh script - bash

Question

I would like to create a variable name as POD inside script to assign kubectl output and then pass this variable while running kubectl port-forward pods..
But I received below error
org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
WorkflowScript: 151: illegal string body character after dollar sign;
solution: either escape a literal dollar sign "\$5" or bracket the value expression "${5}" # line 151, column 80.
e-context ${KUBE_CLUSTER_STAGE}
Here is my script.
environment {
POD = ''
}
steps {
script {
withCredentials([file(credentialsId: 'mbtkubeconfig', variable: 'config')]){
try {
// Expose PostreSQL
sh '''#!/bin/sh
chmod ug+w ${config}
export KUBECONFIG=\${config}
kubectl config use-context ${KUBE_CLUSTER_STAGE}
kubectl config set-context --current --namespace=database
POD = `$(kubectl get po -n database --selector='role==master' -o jsonpath="{.items[0].metadata.name}")`
kubectl port-forward pods/$POD 5432:64000 & echo \$! > filename.txt
'''
When I tried without variable there is no any error.Here is the script running without any error.
sh """#!/bin/sh
chmod ug+w ${config}
export KUBECONFIG=\${config}
kubectl config use-context ${KUBE_CLUSTER_STAGE}
kubectl config set-context --current --namespace=database
kubectl get pods -n database
kubectl port-forward pods/my-postgres-postgresql-helm-0 5432:64000 & echo \$! > filename.txt
"""

Answer 1

When you run commands with sh make sure you are using " not '. Groovy variables will only be resolved when using "${config}".
By the way, it is considered best practice to mark variables with env. although not needed to resolve the variable. For instance, try to mark your cluster stage with ${env.KUBE_CLUSTER_STAGE}