What Is a Jenkinsfile

A Jenkinsfile is a text file that defines your CI/CD pipeline. It lives in your repository and Jenkins reads it automatically.

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Pipeline as Code

Instead of clicking buttons in the Jenkins UI, you write your pipeline in a file.

Benefits:

• Pipeline is version controlled (Git history)
• Changes go through code review (pull requests)
• Pipeline is reproducible across branches
• Easy to share and copy between projects
• Serves as documentation of your build process

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Where to Put It

Place the Jenkinsfile (no extension) in the root of your repository:

my-project/
├── src/
├── tests/
├── Jenkinsfile        ← here
├── README.md
└── pyproject.toml

File name

The default name is Jenkinsfile (capital J, no extension). You can use a custom path in Multibranch Pipeline settings.

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Minimal Jenkinsfile

pipeline {
    agent any

    stages {
        stage('Build') {
            steps {
                echo 'Building...'
            }
        }
        stage('Test') {
            steps {
                echo 'Testing...'
            }
        }
        stage('Deploy') {
            steps {
                echo 'Deploying...'
            }
        }
    }
}

What Each Part Does

Part	Purpose
pipeline { }	Top-level block — wraps everything
agent any	Run on any available Jenkins agent
stages { }	Container for all stages
stage('Name') { }	One logical step (Build, Test, Deploy)
steps { }	Actual commands inside a stage

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How Jenkins Runs It

1. You push code to Git
2. Jenkins detects the change (webhook or polling)
3. Jenkins reads the Jenkinsfile from your branch
4. Jenkins executes each stage in order
5. Results appear in the Jenkins UI (pass/fail, logs, artifacts)

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Pipeline Types

Type	Description	Use Case
Single Branch	One pipeline for one branch	Simple projects
Multibranch	Auto-creates pipelines for each branch	Most projects
Organization Folder	Scans all repos in a GitHub/GitLab org	Large organizations

Use Multibranch Pipeline

Multibranch is the most common choice. It creates a pipeline for every branch that has a Jenkinsfile.

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Running Shell Commands

The most common step is running shell commands:

steps {
    sh 'echo "Hello from shell"'
    sh 'python -m pytest tests/'
    sh '''
        echo "Multi-line script"
        pip install -r requirements.txt
        python -m pytest --cov=src
    '''
}

Step	Platform	Example
sh	Linux / macOS	sh 'make build'
bat	Windows	bat 'msbuild project.sln'
powershell	Windows PowerShell	powershell 'Get-Process'

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Best Practices

• Always store Jenkinsfile in the repository (not in Jenkins UI)
• Use Multibranch Pipeline for most projects
• Keep the Jenkinsfile simple — move complex logic to shell scripts
• Use meaningful stage names that describe what happens
• Start with the minimal example and add features as needed