Branch-specific pipeline behavior in Jenkins - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is branch-specific pipeline behavior in Jenkins?

It means running different pipeline steps or stages depending on which branch of the code repository is being built.

beginner

How can you detect the current branch in a Jenkins pipeline script?

You can use the environment variable 'BRANCH_NAME' inside the pipeline script to get the current branch name.

intermediate

Show a simple Jenkins pipeline snippet that runs a test stage only on the 'develop' branch.

pipeline { agent any stages { stage('Test') { when { branch 'develop' } steps { echo 'Running tests on develop branch' } } } }

beginner

What Jenkins pipeline directive helps to run steps only on a specific branch?

The 'when' directive with the 'branch' condition allows running steps only on a specific branch.

beginner

Why is branch-specific pipeline behavior useful in CI/CD?

It lets you customize builds for different branches, like running full tests on 'main' but only quick checks on feature branches, saving time and resources.

Which environment variable in Jenkins pipeline holds the current branch name?

A GIT_BRANCH

B CURRENT_BRANCH

C BRANCH_NAME

D PIPELINE_BRANCH

BRANCH_NAME is the standard environment variable Jenkins sets for the current branch in multibranch pipelines.

What Jenkins pipeline directive is used to run steps only on a specific branch?

A when

B stage

C agent

D environment

The 'when' directive controls conditional execution, including branch-specific conditions.

In a Jenkins pipeline, how do you specify a stage to run only on the 'main' branch?

A when { branch 'main' }

B if (branch == 'main')

C stage('main')

D agent { label 'main' }

The 'when { branch 'main' }' syntax is the correct way to conditionally run a stage on the 'main' branch.

Why might you want different pipeline behavior on feature branches versus the main branch?

A To deploy feature branches automatically

B To save time by running fewer tests on feature branches

C To disable builds on feature branches

D To merge feature branches automatically

Running fewer or faster tests on feature branches saves build time and resources.

Which Jenkins pipeline syntax supports branch-specific behavior?

A None of the above

B Scripted pipeline only

C Freestyle jobs

D Declarative pipeline

Declarative pipeline syntax includes the 'when' directive for branch-specific conditions.

Explain how to configure a Jenkins pipeline to run different steps on 'main' and 'develop' branches.

Think about using 'when { branch 'branchName' }' inside stages.

Describe why branch-specific pipeline behavior is important in continuous integration.

Consider how different branches have different testing needs.

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