Stash and unstash for passing data in Jenkins - Commands & Configuration

Introduction

When running Jenkins pipelines, sometimes you need to save files or data from one part of the pipeline and use them later in another part. Stash and unstash let you do this easily by temporarily storing files and then retrieving them when needed.

When you want to save build artifacts from one stage to use in a later stage.

When you need to share files between parallel branches in a pipeline.

When you want to pass test reports generated in one step to a publishing step.

When your pipeline runs on different agents and you need to move files between them.

When you want to keep your workspace clean but still keep important files accessible.

Config File - Jenkinsfile

Jenkinsfile

pipeline {
  agent any
  stages {
    stage('Build') {
      steps {
        echo 'Building the project'
        sh 'echo Hello World > greeting.txt'
        stash name: 'greetingFiles', includes: 'greeting.txt'
      }
    }
    stage('Test') {
      steps {
        unstash 'greetingFiles'
        sh 'cat greeting.txt'
      }
    }
  }
}

This Jenkinsfile defines a pipeline with two stages: Build and Test.

In the Build stage, it creates a file named greeting.txt and then stashes it with the name greetingFiles. This saves the file temporarily.

In the Test stage, it unstashes the saved files named greetingFiles, making greeting.txt available again, then prints its content.

Commands

Check that Jenkins CLI or Jenkins Job Builder is installed and accessible before running pipelines.

Terminal

jenkins-jobs --version

Expected Output

jenkins-jobs 3.0.0

Run the Jenkinsfile pipeline locally or on a Jenkins server to execute the stages and test stash/unstash functionality.

Terminal

jenkinsfile-runner -w . -p plugins -f Jenkinsfile

Expected Output

[Pipeline] Start of Pipeline

[Pipeline] stage

[Pipeline] { (Build)

[Pipeline] echo

Building the project

[Pipeline] sh

+ echo Hello World > greeting.txt

[Pipeline] stash

Stashing files with name greetingFiles

[Pipeline] }

[Pipeline] stage

[Pipeline] { (Test)

[Pipeline] unstash

Unstashing files with name greetingFiles

[Pipeline] sh

+ cat greeting.txt

Hello World

[Pipeline] }

[Pipeline] End of Pipeline

Key Concept

If you remember nothing else from this pattern, remember: stash saves files temporarily in one stage, and unstash retrieves them in another stage to share data across pipeline steps.

Common Mistakes

Using unstash with a name that was never stashed.

Jenkins will fail the pipeline because it cannot find the stash with that name.

Always use the exact stash name used in the stash step when calling unstash.

Stashing files that do not exist or are not included by the pattern.

The stash will be empty or missing files, causing errors or missing data later.

Ensure the files exist and the include pattern matches the files you want to stash.

Trying to unstash files in the same stage without stashing first.

Unstash only works for files saved in previous stages or parallel branches, not in the same step.

Use stash in one stage and unstash in a later stage or parallel branch.

Summary

Use stash to save files temporarily during a pipeline stage.

Use unstash to retrieve those files in a later stage or parallel branch.

This helps pass data between different parts of a Jenkins pipeline running on different agents or at different times.

Practice

1. What is the main purpose of stash and unstash in Jenkins pipelines?

easy

A. To temporarily save and later restore files between pipeline stages

B. To permanently store files on the Jenkins master server

C. To delete files after a pipeline stage completes

D. To send notifications when a stage finishes

Solution

1. Step 1: Understand the role of stash

   The stash command saves files temporarily during a pipeline run.

2. Step 2: Understand the role of unstash

   The unstash command restores those saved files in later stages or nodes.

3. Final Answer:

   To temporarily save and later restore files between pipeline stages -> Option A

4. Quick Check:

   stash + unstash = temporary file sharing [OK]

Hint: Remember stash saves, unstash restores files between stages [OK]

Common Mistakes:

• Thinking stash permanently stores files
• Confusing stash with deleting files
• Assuming stash sends notifications

2. Which of the following is the correct syntax to stash files named output.log in a Jenkins pipeline?

easy

A. stash { name: 'logs', files: 'output.log' }

B. stash('logs', 'output.log')

C. stash name = 'logs' include = 'output.log'

D. stash name: 'logs', includes: 'output.log'

Solution

1. Step 1: Recall stash syntax

   The correct stash syntax uses named parameters: stash name: '...', includes: '...'.

2. Step 2: Match options to syntax

   stash name: 'logs', includes: 'output.log' matches the correct syntax exactly.

3. Final Answer:

   stash name: 'logs', includes: 'output.log' -> Option D

4. Quick Check:

   stash uses named params: name and includes [OK]

Hint: Use named parameters: name and includes for stash [OK]

Common Mistakes:

• Using parentheses like a function call
• Using incorrect parameter names like files
• Using assignment (=) instead of colon (:)

3. Given this Jenkins pipeline snippet:

stage('Build') {
  steps {
    sh 'echo Hello > message.txt'
    stash name: 'msg', includes: 'message.txt'
  }
}
stage('Test') {
  steps {
    unstash 'msg'
    sh 'cat message.txt'
  }
}

What will be the output of the cat message.txt command in the Test stage?

medium

A. Hello

B. No such file or directory

C. Empty output

D. Error: stash not found

Solution

1. Step 1: Understand stash saves message.txt

   The Build stage creates message.txt with content 'Hello' and stashes it as 'msg'.

2. Step 2: Unstash restores message.txt in Test stage

   The Test stage unstashes 'msg', restoring message.txt, then runs cat message.txt.

3. Final Answer:

   Hello -> Option A

4. Quick Check:

   unstash restores files, so cat shows 'Hello' [OK]

Hint: Unstash restores files exactly as stashed [OK]

Common Mistakes:

• Assuming unstash does not restore files
• Expecting an error because stages run separately
• Thinking stash deletes files

4. You wrote this Jenkins pipeline snippet:

stage('Build') {
  agent { label 'build' }
  steps {
    sh 'touch file.txt'
    stash name: 'data', includes: 'file.txt'
  }
}
stage('Deploy') {
  agent { label 'deploy' }
  steps {
    unstash 'artifacts'
    sh 'cat file.txt'
  }
}

But the Deploy stage fails with cat: file.txt: No such file or directory. What is the most likely cause?

medium

A. The unstash command is missing in the Deploy stage

B. The file.txt was not created before stashing

C. The stash name used in unstash does not match the stash name

D. The pipeline syntax for stash is incorrect

Solution

1. Step 1: Check stash and unstash names

   The stash is named 'data' but unstash uses 'artifacts', so names do not match.

2. Step 2: Verify file creation and stash syntax

   file.txt is created before stash, unstash command is present, and stash syntax looks correct. Different agents require proper stash/unstash to pass files.

3. Step 3: Identify the cause

   Mismatched names cause unstash to fail silently, so file.txt is not available in Deploy workspace.

4. Final Answer:

   The stash name used in unstash does not match the stash name -> Option C

5. Quick Check:

   stash and unstash names must match exactly [OK]

Hint: Check stash and unstash names match exactly [OK]

Common Mistakes:

• Using different names in stash and unstash
• Forgetting to create the file before stash
• Omitting unstash command in later stage

5. You want to pass multiple files from a Build stage to a Test stage in Jenkins. Which is the best way to stash and unstash these files?

hard

A. stash name: 'allFiles', includes: '*.log, *.txt'
...
unstash 'allFiles'

B. stash name: 'allFiles', includes: '**/*.log, **/*.txt'
...
unstash 'allFiles'

C. stash name: 'allFiles', includes: '**/*.log **/*.txt'
...
unstash 'allFiles'

D. stash name: 'allFiles', includes: '*.log *.txt'
...
unstash 'allFiles'

Solution

1. Step 1: Understand includes pattern syntax

   Jenkins stash supports comma-separated glob patterns with '**/' for recursive matching.

2. Step 2: Compare options

   stash name: 'allFiles', includes: '**/*.log, **/*.txt' ... unstash 'allFiles' uses comma-separated recursive globs, which is correct. Options A, B, and C either lack recursion (A, B) or use spaces instead of commas (B, C). For example, '**/*.log **/*.txt' misses comma separator.

3. Final Answer:

   stash name: 'allFiles', includes: '**/*.log, **/*.txt' ... unstash 'allFiles' -> Option B

4. Quick Check:

   Use comma-separated globs with '**/' for multiple file types [OK]

Hint: Use comma-separated globs with '**/' for multiple files [OK]

Common Mistakes:

• Using spaces instead of commas to separate globs
• Missing recursive '**/' causing files to be skipped
• Incorrect glob syntax causing no files to stash