Learning Jenkins – Part 2: Running Shell Scripts, Parameterized Jobs & GitHub Integration

Now in Part 2, we’ll go a step further:

• Running Shell Scripts with Jenkins

• Creating Parameterized Jobs

• Connecting Jenkins with GitHub for Continuous Integration

By the end of this post, you’ll have a basic CI setup where code pushed to GitHub triggers a Jenkins job.

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Running Shell Scripts in Jenkins

Jenkins can do much more than just printing text — it can install software, run deployments, and execute complex scripts.

Step 1 – Create a Freestyle Job

1. From the Jenkins dashboard → Click New Item

2. Enter a job name (e.g., RunShellJob)

3. Select Freestyle project → Click OK

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Step 2 – Add a Build Step

Scroll to the Build section → Click Add build step → Select Execute Shell

You can either:

• Directly write commands, or

• Point to an existing script file

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Method 1 – Direct Shell Commands

Example: Install Apache web server.

sudo yum install httpd -y
sudo systemctl enable httpd
sudo systemctl start httpd

Good for quick commands.

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Method 2 – Running a Script File

Store commands in a file (e.g., apache.sh) and call it.

apache.sh

#!/bin/bash
sudo yum install httpd -y
sudo systemctl enable httpd
sudo systemctl start httpd
echo "Apache Installed Successfully!"

Make it executable:

chmod +x apache.sh

In Jenkins → Execute Shell → add:

sh /home/ec2-user/apache.sh

Cleaner and reusable.

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Step 3 – Verify

Click Build Now → Check logs in Console Output → Apache should install and run.
Test in browser: http://<EC2-Public-IP>

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Parameterized Builds in Jenkins

Default jobs always run the same way. But what if you need to:

• Deploy different branches (dev, staging, prod)

• Specify an app version

• Run jobs with different inputs

That’s where Parameters help.

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Example 1 – String Parameter

1. Enable: This project is parameterized

2. Add String Parameter:

   • Name: APP_VERSION

   • Default: v1.0.0

3. In Execute Shell:

echo "Deploying Application Version: $APP_VERSION"

At build time, Jenkins asks for input.

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Example 2 – Choice Parameter

1. Add Choice Parameter:

   • Name: BRANCH_NAME

   • Choices:

       dev
       staging
       production
     

2. In Execute Shell:

echo "Building branch: $BRANCH_NAME"

Jenkins shows a dropdown menu during build.

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Example 3 – Conditional Script

Use parameters inside scripts:

if [ "$BRANCH_NAME" == "production" ]; then
  echo "Deploying to Production Server"
  # Prod deployment steps
else
  echo "Deploying to $BRANCH_NAME environment"
  # Other environment deployment steps
fi

One job can serve multiple environments.

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GitHub Integration with Jenkins

Now let’s connect Jenkins with GitHub to trigger builds when code changes.

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Step 1 – Configure GitHub Repository in Jenkins

1. Open your job → Configure

2. Under Source Code Management, select Git

3. Add your GitHub repo URL (HTTPS or SSH)
   Example:

    https://github.com/your-username/sample-app.git
   

4. If private, add GitHub credentials in Jenkins.

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Step 2 – Set Branch

Specify which branch Jenkins should build, e.g., */main.

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Step 3 – Add a Build Step

In Build → Execute Shell, add commands:

echo "Pulling latest code from GitHub..."
ls -l

(We’ll replace this with Maven/Gradle build later.)

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Step 4 – Configure GitHub Webhook

So that Jenkins gets triggered automatically:

1. Go to your GitHub repo → Settings → Webhooks

2. Add webhook:

   • Payload URL: http://<your-jenkins-server>:8080/github-webhook/

   • Content type: application/json

   • Events: Choose “Just the push event”

   • Save

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Step 5 – Enable GitHub Trigger in Jenkins

In Jenkins job config → Build Triggers → Check:
GitHub hook trigger for GITScm polling

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Step 6 – Test the Integration

1. Push code to GitHub

2. Jenkins job should trigger automatically

3. Check Console Output to verify build

Congratulations! You now have basic CI in place.

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Throttling Builds

Sometimes, frequent commits can overload Jenkins.
Solution: Throttle Builds plugin → Limit number of builds at once or per hour.

Example: Allow max 2 builds at a time → others will wait in queue.

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CI/CD Flow with GitHub + Jenkins

Here’s a simple diagram showing how Jenkins fits with GitHub:

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Key Takeaways from Part 2

• Jenkins can run shell commands or execute scripts

• Parameters make jobs flexible & reusable

• GitHub integration enables automated builds on every push

• This forms the foundation of CI pipelines

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This series is my way of learning Jenkins step by step and sharing it as I go.
If you’re following along, try:

• Running a script via Jenkins

• Creating a parameterized job

• Linking Jenkins to your GitHub repo