Environment variables in builds in Jenkins - Mini Project: Build & Apply

Environment variables in builds

📖 Scenario: You are setting up a Jenkins pipeline to build a simple project. You want to use environment variables to store important values like the project name and build number. This helps keep your build script clean and easy to update.

🎯 Goal: Build a Jenkins pipeline script that defines environment variables and uses them in the build steps to print messages with those variables.

📋 What You'll Learn

Create environment variables in the Jenkins pipeline script

Use the environment variables inside the pipeline steps

Print the values of the environment variables during the build

💡 Why This Matters

🌍 Real World

Environment variables in Jenkins pipelines are used to store configuration values like project names, build numbers, and deployment targets. This makes builds flexible and easier to maintain.

💼 Career

Knowing how to use environment variables in Jenkins is essential for DevOps engineers and build managers to create reusable and configurable build pipelines.

1

Define environment variables in the pipeline

Create a Jenkins pipeline script with an environment block that defines two variables: PROJECT_NAME set to MyApp and BUILD_NUMBER set to 42.

Jenkins

pipeline {
    agent any
    environment {
        // Define PROJECT_NAME and BUILD_NUMBER here
    }
    stages {
        stage('Build') {
            steps {
                // Your code here
            }
        }
    }
}

Hint

Use the environment block inside the pipeline to define variables.

2

Use environment variables in a build step

Inside the Build stage's steps, add a script block that assigns a variable called message with the value Building project: ${PROJECT_NAME} - Build number: ${BUILD_NUMBER}.

Jenkins

pipeline {
    agent any
    environment {
        PROJECT_NAME = 'MyApp'
        BUILD_NUMBER = '42'
    }
    stages {
        stage('Build') {
            steps {
                script {
                    // Assign message variable here
                }
            }
        }
    }
}

Hint

Use def message = "Building project: ${PROJECT_NAME} - Build number: ${BUILD_NUMBER}" inside a script block.

3

Print the message variable

Still inside the script block, add a println(message) statement to print the message to the build log.

Jenkins

pipeline {
    agent any
    environment {
        PROJECT_NAME = 'MyApp'
        BUILD_NUMBER = '42'
    }
    stages {
        stage('Build') {
            steps {
                script {
                    def message = "Building project: ${PROJECT_NAME} - Build number: ${BUILD_NUMBER}"
                    // Print the message here
                }
            }
        }
    }
}

Hint

Use println(message) to print the message inside the script block.

4

Run the pipeline and check output

Run the Jenkins pipeline script and verify that the build log shows the line: Building project: MyApp - Build number: 42.

Jenkins

pipeline {
    agent any
    environment {
        PROJECT_NAME = 'MyApp'
        BUILD_NUMBER = '42'
    }
    stages {
        stage('Build') {
            steps {
                script {
                    def message = "Building project: ${PROJECT_NAME} - Build number: ${BUILD_NUMBER}"
                    println(message)
                }
            }
        }
    }
}

// Run the pipeline and check the output in the Jenkins console log

Hint

Look at the Jenkins build console output to see the printed message.

Practice

1. What is the main purpose of environment variables in Jenkins builds?

easy

A. To write the build script itself

B. To display the build logs on the screen

C. To store data like secrets or settings without changing the build code

D. To install Jenkins plugins automatically

Solution

1. Step 1: Understand environment variables role

   Environment variables hold data such as secrets, settings, or dynamic values needed during the build without modifying the build code.

2. Step 2: Identify the correct purpose in Jenkins context

   Jenkins uses environment variables to pass information to builds safely and flexibly.

3. Final Answer:

   To store data like secrets or settings without changing the build code -> Option C

4. Quick Check:

   Environment variables = store build data [OK]

Hint: Environment variables hold build data, not code or logs [OK]

Common Mistakes:

• Confusing environment variables with build scripts
• Thinking environment variables show logs
• Assuming environment variables install plugins

2. Which syntax correctly defines an environment variable named VERSION with value 1.0 in a Jenkins pipeline?

easy

A. environment { VERSION = '1.0' }

B. environment { 'VERSION' = '1.0' }

C. environment { VERSION: '1.0'; }

D. environment { VERSION == '1.0' }

Solution

1. Step 1: Recall Jenkins pipeline environment syntax

   In Jenkins declarative pipelines, environment variables are defined using environment { VAR_NAME = 'value' } syntax.

2. Step 2: Identify correct syntax

   environment { VERSION = '1.0' } uses = which is the correct syntax inside the environment block.

3. Final Answer:

   environment { VERSION = '1.0' } -> Option A

4. Quick Check:

   Use equals sign for key-value in environment block [OK]

Hint: Use = not colon or double equals in environment block [OK]

Common Mistakes:

• Using colon instead of equals sign
• Using double equals which is invalid
• Putting quotes around variable name incorrectly

3. Given this Jenkins pipeline snippet:

pipeline {
  environment {
    BUILD_TYPE = 'release'
  }
  stages {
    stage('Print') {
      steps {
        echo "Build type is: ${BUILD_TYPE}"
      }
    }
  }
}

What will be printed during the build?

medium

A. Error: BUILD_TYPE not defined

B. Build type is: ${BUILD_TYPE}

C. Build type is:

D. Build type is: release

Solution

1. Step 1: Understand environment variable usage in pipeline

   The environment block sets BUILD_TYPE to 'release'. The echo step uses ${BUILD_TYPE} to access this variable.

2. Step 2: Predict output of echo command

   The variable is replaced by its value, so the output will be 'Build type is: release'.

3. Final Answer:

   Build type is: release -> Option D

4. Quick Check:

   Variable expands to value in echo [OK]

Hint: Variables in ${} expand to their values in echo [OK]

Common Mistakes:

• Expecting literal ${BUILD_TYPE} printed
• Thinking variable is empty if not exported
• Assuming error if variable is defined in environment block

4. You wrote this Jenkins pipeline snippet:

pipeline {
  environment {
    API_KEY = SECRET_KEY
  }
  stages {
    stage('Test') {
      steps {
        echo "API key is ${API_KEY}"
      }
    }
  }
}

But the build fails with an error about SECRET_KEY. What is the problem?

medium

A. You must quote the value: API_KEY = "$SECRET_KEY"

B. SECRET_KEY is not defined in Jenkins environment

C. You cannot use environment variables inside environment block directly

D. You should use single quotes instead of double quotes

Solution

1. Step 1: Analyze variable usage in environment block

   The environment block tries to assign API_KEY the value of SECRET_KEY. This requires SECRET_KEY to be defined in Jenkins environment or injected.

2. Step 2: Identify cause of error

   If SECRET_KEY is not defined anywhere, Jenkins cannot resolve it, causing the build to fail.

3. Final Answer:

   SECRET_KEY is not defined in Jenkins environment -> Option B

4. Quick Check:

   Undefined variables cause build errors [OK]

Hint: Ensure referenced env vars exist before using them [OK]

Common Mistakes:

• Assuming quoting fixes undefined variable errors
• Thinking environment block cannot use variables at all
• Using single quotes which prevent variable expansion

5. You want to pass a dynamic build number as an environment variable BUILD_NUM to your Jenkins pipeline and print it. Which snippet correctly achieves this?

hard

A. environment { BUILD_NUM = "${env.BUILD_NUMBER}" }

B. environment { BUILD_NUM == "${env.BUILD_NUMBER}" }

C. environment { BUILD_NUM = env.BUILD_NUMBER; }

D. environment { BUILD_NUM: env.BUILD_NUMBER; }

Solution

1. Step 1: Recall correct syntax for environment variables with dynamic values

   In Jenkins declarative pipelines, environment variables are defined with equals sign syntax and string values. To use a dynamic value like env.BUILD_NUMBER, it must be inside quotes and referenced with ${}.

2. Step 2: Identify correct option

   environment { BUILD_NUM = "${env.BUILD_NUMBER}" } uses BUILD_NUM = "${env.BUILD_NUMBER}" which correctly sets the environment variable to the current build number.

3. Final Answer:

   environment { BUILD_NUM = "${env.BUILD_NUMBER}" } -> Option A

4. Quick Check:

   Use equals sign and ${} for dynamic env vars [OK]

Hint: Use equals sign and ${env.VAR} inside quotes for dynamic vars [OK]

Common Mistakes:

• Using double equals instead of equals sign
• Not quoting the dynamic variable
• Omitting ${} around env variable