creating variable from command output in jenkins pipeline

Preferred one is with temporary file, as it gets success/error code also.

sh "echo foo > result";
def output=readFile('result').trim()
echo "output=$output";

More detailed

stage('Starting Tomcat')
        {
            steps{
            node('master'){
                    sh 'docker run -d -p 9000:8080 tomcatserver > tomcat_server'
                    script
                    {
                        env.containerid = readFile('tomcat_server')
                        sh 'rm -f tomcatserver'
                        sh 'echo Containerd ID of Tomcat $containerid'
                    }
                }
           
            }
           
        }
       
        stage('Stop and Delete Tomcat')
        {
            steps{
            node('master'){
                echo "Stopping ${env.containerid}"
                sh 'docker stop $containerid'
                sh 'docker rm $containerid'
            }
            }
           
        }

 Reference