How To Set Jenkins Pipeline Environment Variables?

pipeline{
    agent any

    stages{
        stage("Env Variables"){
            steps{
                bat ‘set’                                                     
            }
        }
    }
}

pipeline{
    agent any

    stages{
        stage("Env Build Number"){
            steps{
                echo "The build number is ${env.BUILD_NUMBER}"
                echo "You can also use \${BUILD_NUMBER} -> ${BUILD_NUMBER}"                                                
            }
        }
    }
}

import hudson.EnvVars;
import hudson.slaves.EnvironmentVariablesNodeProperty;
import hudson.slaves.NodeProperty;
import hudson.slaves.NodePropertyDescriptor;
import hudson.util.DescribableList;
import jenkins.model.Jenkins;
public createGlobalEnvironmentVariables(String key, String value){

       Jenkins instance = Jenkins.getInstance();

       DescribableList<NodeProperty<?>, NodePropertyDescriptor> globalNodeProperties = instance.getGlobalNodeProperties();
       List<EnvironmentVariablesNodeProperty> envVarsNodePropertyList = globalNodeProperties.getAll(EnvironmentVariablesNodeProperty.class);

       EnvironmentVariablesNodeProperty newEnvVarsNodeProperty = null;
       EnvVars envVars = null;

       if ( envVarsNodePropertyList == null || envVarsNodePropertyList.size() == 0 ) {
           newEnvVarsNodeProperty = new hudson.slaves.EnvironmentVariablesNodeProperty();
           globalNodeProperties.add(newEnvVarsNodeProperty);
           envVars = newEnvVarsNodeProperty.getEnvVars();
       } else {
           envVars = envVarsNodePropertyList.get(0).getEnvVars();
       }
       envVars.put(key, value)
       instance.save()
}
createGlobalEnvironmentVariables('Var1','Dummy')

Username = root
Access_Token = ***************

stage(“reading properties from properties file”) {
    steps {
        // Use a script block to do custom scripting
        script {
            def props = readProperties file: 'extravars.properties' 
            env.Username = props.Username
        }
        echo "The username  is $Username"
    }
}

environment {
       DISABLE_AUTH = 'true'
   }

pipeline {
   agent any
   environment {
       DISABLE_AUTH = 'true'                               //can be used in whole pipeline
   }
   stages {
       stage(“Build”) {
           steps {
               echo env.DISABLE_AUTH
           }
       }
   }
}

pipeline {
   agent any
   environment {
       DISABLE_AUTH = 'true'
   }
   stages {
       stage(“Build”) {
           environment {
                   ENABLE_AUTH = ‘false’                                 //can be used in this stage only
              }
           steps {
               echo env.DISABLE_AUTH
               echo env.ENABLE_AUTH
           }
       }
   }
}

node{
   stage('Build') {
       withEnv(["DISABLE_AUTH=true"]) {
         echo env.DISABLE_AUTH   }
   }
 }

pipeline {
    agent any

    stages {
        stage("capturing output in Environment Variables") {
            steps {
                script {
                    env.LS = bat(script:'dir', returnStdout: true).trim()
                   // if you access environment variable in the batch command
                    echo $LS
                }
            }
        }
    }

pipeline{
    agent any
    environment{
          LT_USERNAME='racha10r@gmail.com'
          LT_ACCESS_KEY='iHnnmi0atXDjDKIqckdBH0gU72Uf8zJb76EyNlXjzvGPzvr54'
          LT_TUNNEL=true
        }
    stages{
        stage('printing the environment variables'){
            steps{
                echo env.LT_USERNAME
                echo env.LT_ACCESS_KEY
                echo env.LT_TUNNEL
            }
        }
    }
}

#!/usr/bin/env groovy

node {
    // Sets the environment variables from LambdaTest for testing
    withEnv(["LT_USERNAME=rachna10r@gmail.com",
    "LT_ACCESS_KEY=z71l7Q9ohS9HhKiCqd690mH0sDu5AYrz8VSB0whO3mZ2JEkNAN",
    "LT_TUNNEL=true"]){

    // Just printing the above set environment variables
    echo env.LT_USERNAME
    echo env.LT_ACCESS_KEY 

   stage('setup') { 

      // Get some code from a GitHub repository
    try{
      git 'https://github.com/LambdaTest/nightwatch-selenium-sample.git'

      //Download Tunnel Binary
     bat 'wget "https://downloads.lambdatest.com/tunnel/v3/windows/64bit/LT_Windows.zip"'

     //Required if unzip is not installed
      bat 'unzip -o LT_Windows.zip'

      //Starting Tunnel Process 
     'LT --user ${LT_USERNAME} --key ${LT_ACCESS_KEY}'
         }
    catch (err){
      echo err
        }
   }
   stage('build') {
      // Installing Dependencies
      bat 'npm install'
      bat 'npm install nightwatch'
    }

   stage('test') {
          try{
        // Running the nightwatch tests with environment set as Chrome
          bat 'node_modules/.bin/nightwatch -e chrome tests'
          }
          catch (err){
          echo err
          }  
   }
   stage('end') {  
    // Printing the success message
     echo "Success" 
     }
 }
}