Environment variables in builds in Jenkins - Commands & Configuration

Introduction

When building software, you often need to use values that can change, like passwords or server addresses. Environment variables let you store these values outside your code so you can reuse and change them easily during the build process.

When you want to keep sensitive data like API keys out of your code.

When you need to use different settings for testing and production builds.

When multiple builds share common settings like server URLs or version numbers.

When you want to pass custom values to scripts or commands during the build.

When you want to avoid hardcoding values that might change often.

Config File - Jenkinsfile

Jenkinsfile

pipeline {
    agent any
    environment {
        APP_ENV = 'production'
        API_KEY = '12345-abcde'
    }
    stages {
        stage('Build') {
            steps {
                echo "Building in environment: ${APP_ENV}"
                sh 'echo API key is $API_KEY'
            }
        }
    }
}

This Jenkinsfile defines a pipeline with environment variables under the environment block.

APP_ENV and API_KEY are set once and used in the build steps.

This keeps sensitive or changeable data outside the code logic but accessible during the build.

Commands

Check that Jenkins CLI or job builder tools are installed and ready to use.

Terminal

jenkins-jobs --version

Expected Output

1.0.0

Start the Jenkins pipeline named 'my-pipeline' which uses environment variables defined in its Jenkinsfile.

Terminal

jenkins-cli build my-pipeline

Expected Output

[Pipeline] Start of Pipeline

[Pipeline] echo

Building in environment: production

[Pipeline] sh

+ echo API key is 12345-abcde

API key is 12345-abcde

[Pipeline] End of Pipeline

Finished: SUCCESS

View the console output of the last build to verify environment variables were used correctly.

Terminal

jenkins-cli console my-pipeline

Expected Output

Building in environment: production

API key is 12345-abcde

Key Concept

If you remember nothing else from this pattern, remember: environment variables let you safely and flexibly pass data into your build without hardcoding it.

Common Mistakes

Hardcoding sensitive values directly in build scripts.

This exposes secrets in code repositories and makes changing values harder.

Use environment variables in the Jenkinsfile or Jenkins credentials store instead.

Referencing environment variables with wrong syntax like ${VAR} in shell steps.

Shell steps require $VAR syntax, so ${VAR} may not expand correctly.

Use $VAR inside shell commands and ${VAR} in Groovy strings.

Defining environment variables inside steps block instead of environment block.

Variables inside steps are not globally available to all stages or steps.

Define environment variables in the pipeline's environment block for global access.

Summary

Define environment variables in the Jenkinsfile environment block to share data across build steps.

Use $VAR syntax inside shell commands and ${VAR} in Groovy strings to access variables.

Run the pipeline and check console output to confirm variables are used correctly.

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