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In this lesson we cover how Jenkins exposes environment variables and how to manage secrets and credentials securely. Environment variables store dynamic values—paths, versions, IDs, and tokens—that pipelines and jobs can reference during builds. There are two main categories of environment variables in Jenkins:
CategoryDescriptionExamples / Notes
Predefined (built-in)Variables Jenkins sets automatically for each build. Useful for metadata and workspace info.BUILD_NUMBER, JOB_NAME, WORKSPACE
User-definedSet globally (Manage Jenkins > Configure System) or per job/pipeline. Available to Declarative and Scripted Pipelines and Freestyle jobs once defined.Set via the UI or environment block in a pipeline
A presentation slide titled "Environment Variables" explaining Jenkins environment variables and showing that they store dynamic values accessible across pipelines. It lists predefined built-in variables (BUILD_NUMBER, JOB_NAME, WORKSPACE) on the left and notes user-defined variables can be set globally or per job on the right.
Example — Declarative Pipeline with a global GREETING environment variable that prints together with the build number: 
pipeline {
    agent any
    environment {
        GREETING = "Hello, world!"
    }
    stages {
        stage('Simple Print') {
            steps {
                // Reference environment variables with ${...}
                echo "${GREETING} Build number: ${BUILD_NUMBER}"
            }
        }
    }
}
Accessing environment variables:
  • In shell steps and many Pipeline steps use the ${VAR} (dollar-curly) syntax, e.g. ${GREETING}.
  • Inside Groovy Pipeline code you can access the same variables via the env map, e.g. env.BUILD_NUMBER or ${env.BUILD_NUMBER} in strings.
Best practice: prefer env.VAR in scripted logic and ${VAR} in step strings to make intent clear. Secure handling of secrets When integrating Jenkins with external services (artifact repositories, cloud providers, APIs, databases), never embed secrets directly in job definitions or source-controlled pipeline files. Use Jenkins’ credentials store to manage sensitive data. Jenkins credentials UI (example):
A dark-themed Jenkins "New credentials" screen showing a form to add credentials (kind, scope, username, password, ID) with a "Create" button. The page header and breadcrumb navigation are visible at the top.
Common credential kinds supported by Jenkins:
Credential KindUse Case / Example
Secret textAPI tokens and personal access tokens (e.g. GH_TOKEN)
Username + passwordBasic auth for services or DB credentials
Secret fileUpload a PEM, config, or other file used at runtime
SSH Username with private keySSH keys for cloning or remote access
CertificatePKCS#12 certificates (optionally with a password)
Plugins may add additional credential types. Credentials are encrypted on the Jenkins controller and referenced in Pipelines by their credential IDs. Give each credential a meaningful, unique ID (for example, mongo-db-creds). Binding credentials in pipelines Use the withCredentials step to fetch and expose credentials only for the lifetime of a block. Example: bind a username/password credential into environment variables and use them in a shell command: 
pipeline {
    agent any
    stages {
        stage('MongoDB Backup') {
            steps {
                withCredentials([usernamePassword(
                    credentialsId: 'mongo-db-creds',
                    usernameVariable: 'MONGO_USER',
                    passwordVariable: 'MONGO_PASSWORD'
                )]) {
                    sh """
                        mongodump --host mongodb.example.com --port 27017 \\
                          --username "${MONGO_USER}" \\
                          --password "${MONGO_PASSWORD}" \\
                          --db mydatabase --out /path/to/backup
                    """
                }
            }
        }
    }
}
How it works:
  • withCredentials looks up the credential by credentialsId and injects the data into the specified environment variables (MONGO_USER, MONGO_PASSWORD) only for the enclosed block.
  • After the block ends, those environment variables are removed — reducing risk of accidental leakage.
Never print secrets or credentials to logs. Avoid echo or sh commands that expose MONGO_PASSWORD or any secret in build output. Use credential masking features and avoid storing secrets in plain text.
Summary
  • Use built-in environment variables for job metadata and the environment block or global settings for custom values.
  • Store all sensitive data in Jenkins Credentials and reference them by ID with withCredentials.
  • Prefer runtime binding and limit the scope where secrets are available to reduce exposure.
Links and references

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