- Functions let you organize and reuse code in your shell scripts like a Middleware and DevOps engineer.
- Instead of repeating logic for Tomcat restarts or Jenkins backups, define it once — then call it from anywhere.
- We'll also explore how to handle errors gracefully inside functions.
📑 Table of Contents
- 💡 What is a Function?
- 🧩 Function Syntax
- Example 1: Basic Function
- Example 2: Function with Parameters
- Example 3: Return Values
- Example 4: Restart Tomcat (with error handling)
- Example 5: Jenkins Backup (with error handling)
- Example 6: WebSphere Log Cleanup
- Example 7: Database Health Check
- Example 8: Modular CI/CD Wrapper Function
- 🏁 Summary
💡 What is a Function?
A function groups commands under one name so you can call them repeatedly. In Middleware automation, you can define restart, deploy, or monitor tasks as reusable functions.
🧩 Function Syntax
function_name() {
commands
}
# OR
function function_name {
commands
}🎯 Example 1: Basic Function
#!/bin/bash
say_hello() {
echo "Hello from MiddlewareBox!"
}
say_hello
💬 Output:
Hello from MiddlewareBox!🧠 Example 2: Function with Parameters
#!/bin/bash
greet_user() {
echo "Welcome $1! You are working on the $2 environment."
}
greet_user Pradeep DevOps
💬 Output:
Welcome Pradeep! You are working on the DevOps environment.📦 Example 3: Function with Return Value
#!/bin/bash
add_numbers() {
sum=$(( $1 + $2 ))
echo $sum
}
result=$(add_numbers 25 30)
echo "The total is: $result"
💬 Output:
The total is: 55🧰 Example 4: Restart Tomcat (with error handling)
#!/bin/bash
restart_tomcat() {
echo "Stopping Tomcat..."
/opt/tomcat/bin/shutdown.sh || { echo "❌ Failed to stop Tomcat"; return 1; }
sleep 3
echo "Starting Tomcat..."
/opt/tomcat/bin/startup.sh || { echo "❌ Failed to start Tomcat"; return 2; }
echo "✅ Tomcat restarted successfully!"
}
restart_tomcat
💬 Output:
Stopping Tomcat...Starting Tomcat...
✅ Tomcat restarted successfully!
If Tomcat fails to start, check
/opt/tomcat/logs/catalina.out.💾 Example 5: Jenkins Backup Function (with error handling)
#!/bin/bash
backup_jenkins() {
backup_dir="/var/jenkins_home/backup"
mkdir -p $backup_dir || { echo "❌ Failed to create backup directory"; return 1; }
tar -czf $backup_dir/jenkins_$(date +%F).tar.gz /var/jenkins_home || { echo "❌ Backup failed"; return 2; }
echo "✅ Backup saved in $backup_dir"
}
backup_jenkins
If backup fails, ensure enough disk space and Jenkins home path is correct.
🧹 Example 6: WebSphere Log Cleanup
#!/bin/bash
cleanup_was_logs() {
log_path="/opt/IBM/WebSphere/AppServer/logs"
echo "Cleaning logs in $log_path"
find $log_path -name "*.log" -type f -mtime +7 -exec rm -f {} \; || echo "⚠️ Cleanup error occurred"
echo "🧹 Old WebSphere logs removed successfully."
}
cleanup_was_logs
If permissions fail, run with sudo or check
AppServer/logs ownership.🧠 Example 7: Database Health Check
#!/bin/bash
check_db() {
if nc -zv dbserver 3306 >/dev/null 2>&1; then
echo "✅ Database reachable"
else
echo "🚨 Database not reachable!"
return 1
fi
}
check_db || echo "⚙️ Please verify DB server or firewall."
🚀 Example 8: Modular CI/CD Wrapper
#!/bin/bash
deploy_app() {
echo "Building app..."
mvn clean package || { echo "❌ Build failed"; return 1; }
echo "Deploying WAR..."
scp target/app.war prod:/opt/tomcat/webapps/ || { echo "❌ Deploy failed"; return 2; }
ssh prod "systemctl restart tomcat"
echo "✅ Deployment complete!"
}
deploy_app
If deploy fails, verify SSH connectivity and WAR path.
🏁 Summary
- Functions make scripts modular, reusable, and easier to maintain.
- Handle errors using
returnand conditional checks. - Great for DevOps: automate Jenkins, Tomcat, WebSphere, and CI/CD pipelines.
- Combine with loops and conditionals from previous lessons for full automation.
