Stash and unstash for passing data in Jenkins - Mini Project: Build & Apply

Passing Data Between Jenkins Pipeline Stages Using Stash and Unstash

📖 Scenario: You are working on a Jenkins pipeline that builds a simple project. You want to save some files in one stage and use them in another stage. This is like packing your lunch in a box (stash) and taking it to school to eat later (unstash).

🎯 Goal: Build a Jenkins pipeline script that creates a file in one stage, stashes it, then unstashes and reads it in the next stage.

📋 What You'll Learn

Create a file named message.txt with the text Hello from stash! in the Build stage

Use stash to save the message.txt file with the name myFiles

In the Test stage, use unstash to retrieve the saved files

Read and print the contents of message.txt in the Test stage

💡 Why This Matters

🌍 Real World

In real Jenkins pipelines, you often need to pass files like build outputs, test reports, or configuration files between stages. Stash and unstash help you do this easily without sharing the whole workspace.

💼 Career

Understanding stash and unstash is essential for Jenkins pipeline developers and DevOps engineers to create efficient, modular, and reliable CI/CD workflows.

1

Create a file in the Build stage

In the Build stage, create a file named message.txt with the text Hello from stash! using the sh step.

Jenkins

pipeline {
    agent any
    stages {
        stage('Build') {
            steps {
                // Create message.txt with text "Hello from stash!"
                // Your code here
            }
        }
    }
}

Hint

Use the sh step to run a shell command that writes text to a file.

2

Stash the file in the Build stage

In the Build stage, after creating message.txt, add a stash step to save the file with the name myFiles and include the file message.txt.

Jenkins

pipeline {
    agent any
    stages {
        stage('Build') {
            steps {
                sh 'echo "Hello from stash!" > message.txt'
                // Stash message.txt with name 'myFiles'
                // Your code here
            }
        }
    }
}

Hint

Use stash name: 'myFiles', includes: 'message.txt' to save the file.

3

Unstash the file in the Test stage

Add a new stage called Test. Inside its steps, use unstash with the name myFiles to retrieve the stashed file.

Jenkins

pipeline {
    agent any
    stages {
        stage('Build') {
            steps {
                sh 'echo "Hello from stash!" > message.txt'
                stash name: 'myFiles', includes: 'message.txt'
            }
        }
        stage('Test') {
            steps {
                // Unstash 'myFiles' here
                // Your code here
            }
        }
    }
}

Hint

Use unstash 'myFiles' inside the Test stage steps.

4

Read and print the file content in the Test stage

In the Test stage, after unstash, add a sh step to print the contents of message.txt using cat message.txt.

Jenkins

pipeline {
    agent any
    stages {
        stage('Build') {
            steps {
                sh 'echo "Hello from stash!" > message.txt'
                stash name: 'myFiles', includes: 'message.txt'
            }
        }
        stage('Test') {
            steps {
                unstash 'myFiles'
                // Print contents of message.txt
                // Your code here
            }
        }
    }
}

Hint

Use sh 'cat message.txt' to display the file content in the console.

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