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

Accessing Environment Variables in Jenkins Pipeline

📖 Scenario: You are setting up a Jenkins pipeline to automate a build process. You need to access environment variables inside the pipeline script to customize the build steps.

🎯 Goal: Build a Jenkins pipeline script that accesses and prints specific environment variables.

📋 What You'll Learn

Create a Jenkins pipeline script with a pipeline block

Access the environment variable BUILD_NUMBER

Access the environment variable MY_VAR

Print both environment variables using echo steps

💡 Why This Matters

🌍 Real World

Jenkins pipelines often need environment variables to customize builds, pass secrets, or configure deployment settings.

💼 Career

Understanding environment variables in Jenkins is essential for DevOps engineers to automate and manage CI/CD pipelines effectively.

1

Create a basic Jenkins pipeline skeleton

Write a Jenkins pipeline script starting with a pipeline block and a agent any directive.

Jenkins

pipeline {
    agent any
    // Your code here
}

Hint

Start by writing pipeline { and inside it add agent any to run on any available agent.

2

Add an environment block to define environment variables

Inside the pipeline block, add an environment block that defines a variable MY_VAR with the value hello.

Jenkins

pipeline {
    agent any
    environment {
        // Your code here
    }
}

Hint

Use the environment block inside pipeline and define MY_VAR = 'hello'.

3

Access and print environment variables in a stage

Add a stage named 'Print Env' with a steps block that uses echo to print BUILD_NUMBER and MY_VAR environment variables using env.BUILD_NUMBER and env.MY_VAR.

Jenkins

pipeline {
    agent any
    environment {
        MY_VAR = 'hello'
    }
    // Your code here
}

Hint

Inside stages, add a stage('Print Env') with steps that use echo to print env.BUILD_NUMBER and env.MY_VAR.

4

Print the environment variables output

Run the pipeline script and ensure the console output shows the lines Build number is: followed by the build number and My variable is: hello.

Jenkins

pipeline {
    agent any
    environment {
        MY_VAR = 'hello'
    }
    stages {
        stage('Print Env') {
            steps {
                // Your code here
            }
        }
    }
}

Hint

Run the pipeline and check the console output for the expected lines.

Practice

1. In a Jenkins Pipeline script, how do you access an environment variable named BUILD_NUMBER?

easy

A. Using BUILD_NUMBER directly without prefix

B. Using env.BUILD_NUMBER

C. Using getEnv('BUILD_NUMBER')

D. Using $BUILD_NUMBER inside the script block

Solution

1. Step 1: Understand Jenkins environment variable access

   Jenkins Pipeline exposes environment variables via the env object.

2. Step 2: Access the variable using the correct syntax

   You access BUILD_NUMBER as env.BUILD_NUMBER in the script.

3. Final Answer:

   Using env.BUILD_NUMBER -> Option B

4. Quick Check:

   env.VARIABLE_NAME = correct access [OK]

Hint: Always prefix environment variables with env. in Jenkins [OK]

Common Mistakes:

• Trying to use variable name without env prefix
• Using shell-style $VARIABLE inside Groovy script
• Calling non-existent getEnv() method

2. Which of the following is the correct syntax to print the environment variable JOB_NAME in a Jenkins Pipeline script block?

easy

A. println("JOB_NAME")

B. echo $JOB_NAME

C. println(env.JOB_NAME)

D. print(JOB_NAME)

Solution

1. Step 1: Identify the correct way to print env variables in Groovy script

   In Jenkins Pipeline Groovy scripts, use println(env.VARIABLE) to print environment variables.

2. Step 2: Check each option

   println("JOB_NAME") prints the string "JOB_NAME" literally. echo $JOB_NAME uses shell syntax, invalid in Groovy. print(JOB_NAME) attempts to print JOB_NAME directly, but it's not available in Groovy scope without env prefix.

3. Final Answer:

   println(env.JOB_NAME) -> Option C

4. Quick Check:

   Use println(env.VARIABLE) to print env vars in script [OK]

Hint: Use println(env.VARIABLE) inside script blocks [OK]

Common Mistakes:

• Using shell syntax like $VARIABLE inside Groovy
• Printing variable name as string instead of value
• Trying to access variables without env. prefix

3. Given this Jenkins Pipeline snippet:

pipeline {
  agent any
  stages {
    stage('Print Env') {
      steps {
        script {
          echo "Branch is: ${env.BRANCH_NAME}"
        }
      }
    }
  }
}

What will be the output if the environment variable BRANCH_NAME is set to feature-123?

medium

A. Branch is: feature-123

B. Branch is: ${env.BRANCH_NAME}

C. Branch is: BRANCH_NAME

D. Error: BRANCH_NAME not found

Solution

1. Step 1: Understand string interpolation in Jenkins Pipeline

   Using double quotes with ${env.BRANCH_NAME} interpolates the variable value.

2. Step 2: Substitute the environment variable value

   Since BRANCH_NAME is set to "feature-123", the output will be "Branch is: feature-123".

3. Final Answer:

   Branch is: feature-123 -> Option A

4. Quick Check:

   Double quotes + ${env.VAR} = variable value [OK]

Hint: Use double quotes and ${env.VAR} for variable interpolation [OK]

Common Mistakes:

• Using single quotes which prevent interpolation
• Printing variable name literally without ${}
• Assuming env variables are undefined

4. You wrote this Jenkins Pipeline snippet:

pipeline {
  agent any
  environment {
    MY_VAR = 'hello'
  }
  stages {
    stage('Test') {
      steps {
        script {
          echo env.MY_VAR
        }
      }
    }
  }
}

But the output is empty. What is the likely cause?

medium

A. The environment block syntax is incorrect; use MY_VAR='hello' with quotes and no spaces around =

B. Environment variables must be accessed as env['MY_VAR'] not env.MY_VAR

C. The environment variable was not set correctly; use MY_VAR='hello' without spaces

D. You cannot access environment variables inside script blocks

Solution

1. Step 1: Check environment block syntax

   In Jenkins Pipeline, environment variables must be assigned with no spaces around = and values in quotes, like MY_VAR='hello'.

2. Step 2: Identify the syntax error in the snippet

   The snippet uses MY_VAR = 'hello' with spaces around = which is invalid and causes the variable not to be set.

3. Final Answer:

   The environment block syntax is incorrect; use MY_VAR='hello' with quotes and no spaces around = -> Option A

4. Quick Check:

   Use no spaces around = in environment block [OK]

Hint: No spaces around = in environment block assignments [OK]

Common Mistakes:

• Adding spaces around = in environment variable assignment
• Trying to access env vars incorrectly
• Assuming script block can't access env vars

5. You want to pass a secret API key stored as an environment variable API_KEY to a shell command in Jenkins Pipeline. Which is the best way to do this securely?

hard

A. Use sh "curl -H 'Authorization: Bearer $API_KEY' https://api.example.com"

B. Use sh(script: "curl -H 'Authorization: Bearer ${env.API_KEY}' https://api.example.com")

C. Use sh(script: "curl -H 'Authorization: Bearer $API_KEY' https://api.example.com", environment: [API_KEY: env.API_KEY])

D. Use Jenkins credentials binding plugin to inject API_KEY and access it as env.API_KEY inside sh

Solution

1. Step 1: Understand secure handling of secrets in Jenkins

   Secrets like API keys should be stored in Jenkins credentials and injected securely, not hardcoded or exposed in logs.

2. Step 2: Use credentials binding plugin

   This plugin injects secrets as environment variables during the build, accessible as env.API_KEY inside sh without exposing them in logs.

3. Final Answer:

   Use Jenkins credentials binding plugin to inject API_KEY and access it as env.API_KEY inside sh -> Option D

4. Quick Check:

   Use credentials plugin for secrets, not plain env vars [OK]

Hint: Use Jenkins credentials plugin for secrets, not plain env vars [OK]

Common Mistakes:

• Passing secrets directly in shell commands risking exposure
• Using string interpolation exposing secrets in logs
• Not using Jenkins credentials plugin for sensitive data