pipeline {

    environment {
        registry = "test/testnginx1"
        registryCredential = 'dockerhub-creds'
        dockerImage = ''
        }
    agent { label 'jenkins-slave' }
    stages {
      stage('Building image') {
                steps{
                  script {
                    dockerImage = docker.build registry + ":latest"
                  }
                }
              }
      stage('Push image to registry') {
           steps{
              script {
                 docker.withRegistry( '', registryCredential ) {
                 dockerImage.push()
               }
             }
           }
         }
      }
  }

return (["DO NOT UPDATE"] + sout.tokenize())

+ docker build -t test/test1nginx:latest .
/home/jenkins/agent/workspace/test-pipelines4@tmp/durable-4de421ac/script.sh: 1: /home/jenkins/agent/workspace/test-pipelines4@tmp/durable-4de421ac/script.sh: docker: not found