Branch-specific pipeline behavior in Jenkins - Mini Project: Build & Apply

Branch-specific pipeline behavior

📖 Scenario: You work in a team that uses Jenkins to automate software builds. Different branches in your code repository need different build steps. For example, the main branch runs full tests, but feature branches run only quick checks.

🎯 Goal: Build a Jenkins pipeline script that runs different steps depending on the branch name. You will create a variable for the branch, set a condition to check the branch, and run branch-specific commands.

📋 What You'll Learn

Create a variable branchName to hold the branch name.

Add a condition to check if branchName is 'main'.

Run a shell command echo "Running full tests" if on main branch.

Run a shell command echo "Running quick checks" if on any other branch.

Print a message showing which branch is being built.

💡 Why This Matters

🌍 Real World

Teams use branch-specific pipelines to run different tests or deployments depending on the code branch, saving time and resources.

💼 Career

Knowing how to write conditional Jenkins pipelines is a key skill for DevOps engineers to automate CI/CD workflows efficiently.

1

Set the branch name variable

Create a variable called branchName and set it to the string 'main'.

Jenkins

# Create a variable called branchName and set it to 'main'
# Your code here

Hint

Use def branchName = 'main' to create the variable.

2

Add a condition to check the branch

Add an if statement that checks if branchName is equal to 'main'.

Jenkins

def branchName = 'main'
// Add an if statement to check if branchName == 'main'
// Your code here

Hint

Use if (branchName == 'main') to check the branch.

3

Add branch-specific shell commands

Inside the if block, add sh 'echo "Running full tests"'. Add an else block with sh 'echo "Running quick checks"'.

Jenkins

def branchName = 'main'
if (branchName == 'main') {
    // Add shell command for main branch
} else {
    // Add shell command for other branches
}

Hint

Use sh 'echo "Running full tests"' inside the if block and sh 'echo "Running quick checks"' inside the else block.

4

Print the branch being built

Add a println statement after the if-else block to print "Building branch: " followed by the branchName variable.

Jenkins

def branchName = 'main'
if (branchName == 'main') {
    sh 'echo "Running full tests"'
} else {
    sh 'echo "Running quick checks"'
}
// Print the branch name
# Your code here

Hint

Use println("Building branch: ${branchName}") to print the branch name.

Practice

1.

Which Jenkins pipeline syntax runs a stage only on the main branch?

easy

A. branch == 'main' { runStage() }

B. if (branch == 'main')

C. onlyIf branch == 'main'

D. when { branch 'main' }

Solution

1. Step 1: Understand Jenkins branch condition syntax

   Jenkins uses when { branch 'branchName' } to run stages on specific branches.

2. Step 2: Match syntax to run on main branch

   The correct syntax is when { branch 'main' } to target the main branch.

3. Final Answer:

   when { branch 'main' } -> Option D

4. Quick Check:

   Branch condition = when { branch 'main' } [OK]

Hint: Use 'when { branch "branchName" }' for branch-specific stages [OK]

Common Mistakes:

• Using if statements instead of 'when' block
• Incorrect syntax like 'onlyIf' or inline conditions
• Confusing branch name quotes or missing quotes

2.

Which snippet correctly uses Jenkins declarative pipeline syntax to run a stage only on branches dev or feature/*?

stage('Test') {
  when {
    ???
  }
  steps {
    echo 'Running tests'
  }
}

easy

A. anyOf { branch 'dev'; branch 'feature/*' }

B. branch 'dev' && branch 'feature/*'

C. allOf { branch 'dev'; branch 'feature/*' }

D. branch 'dev' || branch 'feature/*'

Solution

1. Step 1: Identify correct syntax for multiple branch conditions

   Jenkins uses anyOf { branch 'name'; branch 'pattern' } to run if any branch matches.

2. Step 2: Choose syntax matching either 'dev' or 'feature/*'

   Using anyOf { branch 'dev'; branch 'feature/*' } runs the stage on either branch.

3. Final Answer:

   anyOf { branch 'dev'; branch 'feature/*' } -> Option A

4. Quick Check:

   Multiple branches = anyOf with branch conditions [OK]

Hint: Use anyOf { branch 'x'; branch 'y' } for multiple branches [OK]

Common Mistakes:

• Using logical operators like || or && directly inside when
• Using allOf which requires all conditions true
• Incorrect syntax without braces or semicolons

3.

Given this Jenkins pipeline snippet, what will be the output if the branch is feature/login?

pipeline {
  agent any
  stages {
    stage('Build') {
      when { branch 'main' }
      steps { echo 'Building main branch' }
    }
    stage('Test') {
      when { branch 'feature/*' }
      steps { echo 'Testing feature branch' }
    }
  }
}

medium

A. Testing feature branch

B. Building main branch

C. Building main branch\nTesting feature branch

D. No output

Solution

1. Step 1: Check branch conditions for each stage

   'Build' runs only on 'main' branch; 'Test' runs on branches matching 'feature/*'.

2. Step 2: Match current branch 'feature/login'

   'feature/login' matches 'feature/*', so only 'Test' stage runs and prints 'Testing feature branch'.

3. Final Answer:

   Testing feature branch -> Option A

4. Quick Check:

   Branch 'feature/login' matches 'feature/*' only [OK]

Hint: Match branch patterns carefully to predict stage execution [OK]

Common Mistakes:

• Assuming 'main' stage runs on all branches
• Ignoring wildcard pattern matching
• Expecting both stages to run always

4.

Identify the error in this Jenkins pipeline snippet that tries to run a stage only on the release branch:

stage('Deploy') {
  when {
    branch release
  }
  steps {
    echo 'Deploying release branch'
  }
}

medium

A. Steps block should be outside the stage

B. Incorrect stage name 'Deploy'

C. Missing quotes around branch name in when condition

D. Branch condition should be inside steps

Solution

1. Step 1: Review syntax for branch condition in when block

   The branch name must be a string inside quotes: branch 'release'.

2. Step 2: Identify missing quotes causing syntax error

   Here, branch release lacks quotes, causing a syntax error.

3. Final Answer:

   Missing quotes around branch name in when condition -> Option C

4. Quick Check:

   Branch names need quotes in when { branch 'name' } [OK]

Hint: Always quote branch names in when { branch 'name' } [OK]

Common Mistakes:

• Omitting quotes around branch names
• Placing steps outside stage block
• Misplacing branch condition inside steps

5.

You want a Jenkins pipeline stage to run on all branches except main and develop. Which when condition correctly implements this?

hard

A. allOf { not branch 'main'; not branch 'develop' }

B. not { anyOf { branch 'main'; branch 'develop' } }

C. anyOf { not branch 'main'; not branch 'develop' }

D. branch != 'main' && branch != 'develop'

Solution

1. Step 1: Understand negation of multiple branches

   To exclude branches, wrap the branches in anyOf and negate with not.

2. Step 2: Apply correct syntax for excluding 'main' and 'develop'

   not { anyOf { branch 'main'; branch 'develop' } } runs on all branches except these two.

3. Final Answer:

   not { anyOf { branch 'main'; branch 'develop' } } -> Option B

4. Quick Check:

   Exclude branches = not { anyOf { ... } } [OK]

Hint: Use not { anyOf { branch 'x'; branch 'y' } } to exclude branches [OK]

Common Mistakes:

• Using allOf with negations incorrectly
• Using logical operators like && directly
• Misplacing not inside anyOf instead of outside