What is Continuous Integration in Jenkins - CLI Guide

Introduction

Continuous Integration helps developers merge their code changes frequently into a shared project. It automatically tests and builds the code to catch problems early, making software development smoother and faster.

When multiple developers work on the same project and need to combine their code regularly without conflicts

When you want to automatically check that new code does not break existing features

When you want to speed up feedback on code quality after each change

When you want to avoid long manual testing and integration steps before releasing software

When you want to keep your software always ready to deploy

Commands

Starts the Jenkins server which will run the Continuous Integration jobs.

Terminal

java -jar jenkins.war

Expected Output

Running from: /home/user/jenkins.war

Jenkins is fully up and running

Creates a new Jenkins job named 'example-job' using the configuration file 'job-config.xml'. This job will run builds automatically.

Terminal

curl -X POST http://localhost:8080/createItem?name=example-job --header "Content-Type: application/xml" --data-binary @job-config.xml

Expected Output

No output (command runs silently)

→

-X POST - Specifies the HTTP method to create the job

→

--header "Content-Type: application/xml" - Sets the content type to XML for the job configuration

Triggers a build of the 'example-job' manually to test the Continuous Integration process.

Terminal

java -jar jenkins-cli.jar -s http://localhost:8080 build example-job

Expected Output

[example-job] Started by user

Building in workspace /var/lib/jenkins/workspace/example-job

Finished: SUCCESS

→

-s - Specifies the Jenkins server URL

Shows the console output of the last build of 'example-job' to check build details and test results.

Terminal

java -jar jenkins-cli.jar -s http://localhost:8080 console example-job

Expected Output

[Pipeline] Start of Pipeline

[Pipeline] echo

Building project...

[Pipeline] End of Pipeline

Finished: SUCCESS

→

-s - Specifies the Jenkins server URL

Key Concept

If you remember nothing else from Continuous Integration, remember: it automatically tests and builds your code every time you change it to catch problems early.

Common Mistakes

Not starting the Jenkins server before running commands

Commands fail because Jenkins is not running to accept requests

Always start Jenkins with 'java -jar jenkins.war' before creating jobs or triggering builds

Using incorrect job configuration XML when creating a job

Jenkins rejects the job creation or the job fails to run properly

Use a valid, tested job-config.xml file with correct syntax and settings

Not checking build console output after triggering a build

You miss errors or test failures that cause the build to fail

Always review the console output to verify build success and troubleshoot issues

Summary

Start Jenkins server to enable Continuous Integration jobs.

Create a Jenkins job with a configuration file to define build steps.

Trigger builds manually or automatically to test code changes.

Check build console output to verify success and find errors.