🐧 Linux Shell Scripting for Beginners – Complete Tutorial Series.

• A 13-part practical shell scripting course for DevOps and Middleware Engineers.

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💡 How This Tutorial Series Will Help You

• ✔ Build a strong foundation in Linux Shell scripting — from basics to automation.
• ✔ Automate daily Middleware and DevOps tasks: monitoring, backups, and log management.
• ✔ Write scripts for Middleware platforms like Tomcat, Jenkins, and WebSphere.
• ✔ Debug, schedule, and manage production-ready shell scripts confidently.
• ✔ Perfect for Sysadmins, Middleware, and DevOps Engineers upgrading to Cloud roles.

📚 Complete Course Index

🐚 Part 1: What is a Variable?

Learn how variables store data and simplify automation scripts. Foundation of all shell logic.

📥 Part 2: Reading User Input in Shell

Make interactive scripts using read command with Jenkins and Tomcat examples.

🧩 Part 3: Conditional Statements (if, elif, else)

Use decision-making in your scripts with examples checking files, services, and network health.

🔁 Part 4: Loops in Shell (for, while, until)

Automate repetitive DevOps tasks like log cleanup, backups, and status monitoring.

⚙️ Part 5: Functions in Shell (Reusable Scripts)

Write modular, reusable functions — restart Tomcat or back up Jenkins in one click.

📦 Part 6: Arrays & Arguments

Store multiple values, manage user inputs, and process server lists in scripts.

📁 Part 7: File Handling in Shell

Learn how to read, write, append, and handle configuration or log files safely.

💡 Part 8: Debugging & Logging

Find and fix script errors, use logs, and enable debug mode for safe execution.

🕒 Part 9: Scheduling & Automation

Use cron and @reboot jobs to run scripts automatically for health checks or backups.

🎯 Part 10: Middleware Health Monitoring Project

Create a production-ready monitoring script for Tomcat, Jenkins, and NGINX with auto-restart.

🧾 Part 11: Log Management & Rotation

Automate log rotation with logrotate and custom retention scripts for Middleware systems.

💾 Part 12: Backup & Restore Automation Project

Perform automated backup and restore for Jenkins, Tomcat, and WebSphere with rollback support.

⚙️ Part 13: Subshells, Process Control & Parallel Execution

Run multiple jobs in parallel, monitor background processes, and speed up automation workflows.

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🚀 Why MiddlewareBox Shell Scripting Series?

• ✅ Step-by-step, beginner-friendly explanations.
• ✅ Each topic includes real DevOps & Middleware context.
• ✅ Examples with Output and Error handling.
• ✅ Simple language for better understanding.

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✨ Start Learning Now → Part 1: What is a Variable?
& build your own scripts from scratch! 💪

🎯Shell Scripting for Beginners – Part 10: Middleware Health Monitoring Project (Mixed Example).

• This is our final, beginner-friendly project 🎯 — where we'll combine everything you've learned: variables, if-else, loops, functions, logging, and cron automation.
• Let's create a simple Middleware Health Monitoring script that checks Tomcat, Jenkins, Docker, MySQL, and SSL expiry.

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📑 Table of Contents

• 1️⃣ Overview
• 2️⃣ Full Simple Script
• 3️⃣ Example Output
• 4️⃣ Automate the Script

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1️⃣ Overview

This script uses:

• Variables – store names, logs, and domains.
• Functions – reusable checks for each service.
• If-Else – to decide if a service needs restart.
• For loop – to check multiple Docker containers.
• While loop – to retry connection.
• Logs – write output to a file.

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2️⃣ Full Middleware Health Monitoring Script

#!/bin/bash
# MiddlewareBox - Simple Health Monitor

LOG="/var/log/middleware_health.log"
domain="middlewarebox.com"
echo "===== Middleware Health Check =====" >> $LOG
date >> $LOG

# --- Function to check Tomcat ---
check_tomcat() {
  echo "Checking Tomcat..."
  if pgrep -f "org.apache.catalina.startup.Bootstrap" > /dev/null; then
     echo "✅ Tomcat is running" | tee -a $LOG
  else
     echo "🚨 Tomcat is down, restarting..." | tee -a $LOG
     /opt/tomcat/bin/startup.sh
     echo "✅ Tomcat restarted" | tee -a $LOG
  fi
}

# --- Function to check Jenkins ---
check_jenkins() {
  echo "Checking Jenkins..."
  if systemctl is-active --quiet jenkins; then
     echo "✅ Jenkins is active" | tee -a $LOG
  else
     echo "🚨 Jenkins not running, restarting..." | tee -a $LOG
     systemctl restart jenkins
     echo "✅ Jenkins restarted" | tee -a $LOG
  fi
}

# --- Function to check MySQL ---
check_db() {
  echo "Checking MySQL..."
  if mysql -u root -pSecret -e "show databases;" > /dev/null 2>&1; then
     echo "✅ MySQL connection successful" | tee -a $LOG
  else
     echo "🚨 MySQL connection failed" | tee -a $LOG
     echo "Retrying in 5 seconds..."
     sleep 5
     mysql -u root -pSecret -e "show databases;" && echo "✅ MySQL reconnected" | tee -a $LOG
  fi
}

# --- Check Docker Containers using FOR Loop ---
check_docker() {
  echo "Checking Docker containers..."
  for c in nginx webapp db
  do
    status=$(docker inspect -f '{{.State.Status}}' $c 2>/dev/null)
    if [ "$status" != "running" ]; then
      echo "🚨 Container $c is $status, restarting..." | tee -a $LOG
      docker start $c
    else
      echo "✅ Container $c is running" | tee -a $LOG
    fi
  done
}

# --- Check SSL certificate expiry ---
check_ssl() {
  echo "Checking SSL expiry..."
  expiry=$(echo | openssl s_client -servername $domain -connect $domain:443 2>/dev/null | openssl x509 -noout -dates | grep notAfter | cut -d= -f2)
  days_left=$(( ($(date -d "$expiry" +%s) - $(date +%s)) / 86400 ))
  if [ $days_left -le 15 ]; then
    echo "⚠️ SSL expires in $days_left days!" | tee -a $LOG
  else
    echo "✅ SSL valid for $days_left days" | tee -a $LOG
  fi
}

# --- MAIN EXECUTION FLOW ---
check_tomcat
check_jenkins
check_db
check_docker
check_ssl

echo "✅ Health check completed successfully!" | tee -a $LOG
echo "========================================" >> $LOG

💬 Example Output:

✅ Tomcat is running
✅ Jenkins is active
✅ MySQL connection successful
✅ Container nginx is running
✅ SSL valid for 70 days
✅ Health check completed successfully!

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3️⃣ Automate the Script

# Run every 30 minutes
*/30 * * * * /opt/scripts/middleware_health.sh >> /var/log/health_cron.log 2>&1

# Run automatically on system reboot
@reboot /opt/scripts/middleware_health.sh >> /var/log/boot_health.log 2>&1

💬 Output (Cron log):

[BOOT] Health check executed
✅ All services healthy

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🏁 Summary

• ✅ Combined all major shell scripting concepts.
• ✅ Checks Tomcat, Jenkins, Docker, MySQL, and SSL in one file.
• ✅ Uses if, for, functions, and basic while retry logic.
• ✅ Can run manually or via cron / reboot automation.

← Previous: Part 9 – Scheduling & Automation Next: Part 11 – Log Management & Rotation →

📁 Shell Scripting for Beginners – Part 7: File Handling in Shell.

• In Middleware & DevOps automation, file handling is everywhere — reading logs, writing reports, rotating backups, or watching live output.
• Let's learn how to read, write, append, and monitor files in shell scripts with real-world Middleware examples.

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📑 Table of Contents

• Reading Files
• Writing & Appending Files
• Monitoring Log Files
• Error Handling & Debug Tips
• Summary

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📖 1️⃣ Reading Files

Example 1: Read File Line by Line

#!/bin/bash
filename="/opt/scripts/serverlist.txt"
while read -r line; do
  echo "Processing server: $line"
done < "$filename"

💬 Output:

Processing server: app1
Processing server: app2
Processing server: app3

Example 2: Display Tomcat Log Errors

#!/bin/bash
grep "ERROR" /opt/tomcat/logs/catalina.out

💬 Output:

ERROR [localhost-startStop-1] ... Application failed to start
ERROR [main] ... Database connection refused

💡 Tip: Use grep -i error to ignore case.

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✍️ 2️⃣ Writing & Appending Files

Example 3: Write Output to File

#!/bin/bash
echo "Backup started at $(date)" > /opt/scripts/backup.log
echo "Compressing files..." >> /opt/scripts/backup.log
tar -czf /tmp/backup.tar.gz /opt/data && echo "Backup successful" >> /opt/scripts/backup.log

💬 Output File Content:

Backup started at Sat Nov 1 02:00:00 IST 2025
Compressing files...
Backup successful

Example 4: Append Deployment Status

#!/bin/bash
env=$1
status=$2
echo "$(date) - $env deployment $status" >> /opt/scripts/deploy_history.log

💬 Output File Content:

Sat Nov 1 02:15:00 IST 2025 - dev deployment SUCCESS
Sat Nov 1 02:17:00 IST 2025 - prod deployment FAILED

Example 5: Log WebSphere Cleanup Activity

#!/bin/bash
logfile="/opt/IBM/WebSphere/AppServer/logs/cleanup.log"
echo "$(date): Cleaning old logs..." >> $logfile
find /opt/IBM/WebSphere/AppServer/logs -type f -mtime +7 -delete && echo "✅ Logs cleaned" >> $logfile

💬 Output File:

Sat Nov 1 02:30:00 IST 2025: Cleaning old logs...
✅ Logs cleaned

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🔍 3️⃣ Monitoring Log Files

Example 6: Live Tail of Tomcat Logs

#!/bin/bash
echo "Monitoring Tomcat logs..."
tail -f /opt/tomcat/logs/catalina.out

💬 Output:

Monitoring Tomcat logs...
[INFO] Server startup completed in 2200 ms
[WARN] Deprecated API in use
[ERROR] Connection timeout to DB

Example 7: Auto-restart Jenkins on Log Failure

#!/bin/bash
tail -Fn0 /var/log/jenkins/jenkins.log | \
while read line; do
  echo "$line" | grep "ERROR" &>/dev/null
  if [ $? = 0 ]; then
    echo "🚨 Error detected, restarting Jenkins..."
    systemctl restart jenkins
  fi
done

💬 Output:

[ERROR] Jenkins job queue stuck
🚨 Error detected, restarting Jenkins...

Example 8: Monitor NGINX Access Logs for High Load

#!/bin/bash
tail -n 100 /var/log/nginx/access.log | awk '{print $9}' | sort | uniq -c

💬 Output:

500 3
404 7
200 90
301 5

💡 Tip: Use this for quick traffic analysis on your Middleware or DevOps pipeline servers.

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⚠️ 4️⃣ Error Handling & Debugging

• Use set -e to exit on first failure.
• Redirect errors → 2>> error.log to capture exceptions.
• Validate file existence before reading:

if [ ! -f "$filename" ]; then
  echo "❌ File not found: $filename"
  exit 1
fi

If your script suddenly exits, check for missing files or permission issues in /var/log/messages or your custom error log.

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🏁 Summary

• Read files line by line to automate configuration or host processing.
• Write and append logs for auditing and historical tracking.
• Monitor live logs (Tomcat, Jenkins, NGINX) using tail -f.
• Add error handling to avoid silent file issues in production.

← Previous: Part 6 – Arrays & Arguments Next: Part 8 – Debugging & Logging →

Monitor Apache httpd Proxy balancer-manager status

Step 1: For  Proxy balancer-manager status add below configuration in httpd.conf

Note: Enable "mod_status" module

###########################################

LoadModule status_module modules/mod_status.so 

<Location "/balancer-manager">

    SetHandler balancer-manager

    Order deny,allow

    Deny from all

    Allow from localhost 192.168.0.103

</Location>

ProxyPass /balancer-manager !

###########################################

Screenshot-1:

Screenshot-2:

Screenshot-3:

Reference link:

•  ·         https://httpd.apache.org/docs/2.4/mod/mod_proxy_balancer.htm
•  ·         https://httpd.apache.org/docs/2.4/howto/reverse_proxy.html
•        https://access.redhat.com/documentation/
•        'HTTP Status Codes - Code A Site Resource

Learn, How to configure, Apache Configure mod_proxy as load balancer (LB)- JBoss 7.1

Thanks :-)

How to monitor Apache httpd ModJK status

Step 1: For Jk Status Manager status add below configuration in httpd.conf

Note: Enable "mod_status" module

############################################

LoadModule status_module modules/mod_status.so 

<Location "/jkstatus">

    JkMount status

    Order deny,allow

    Deny from all

    Allow from localhost 192.168.xxx.xxx

</Location>

JkMount   /jkstatus/*  status

############################################

Step 2: Edit workers.properties file  and add (status)  on worker & worker.list


## Status worker for managing load balancer

       worker.status.type=status

# #Define list of workers that will be used
# #for mapping requests

      worker.list=loadbalancer,status

Step 3: Use https://localhost/jkstatus

Reference link:  https://access.redhat.com/documentation/Mod_jk/Httpd

                              HTTP Status Codes - Code A Site Resource

Learn, 

How to configure Apache mod_jk HTTP Connector - JBOSS AS 7.1

Thanks :-)

Monitor Apache httpd process/thread status

Step 1: Enable "mod_status" module on $apache_home/conf/httpd.conf file.


Step 2: Add below lines to get status of  Apache server.


####################################

LoadModule status_module modules/mod_status.so 
ExtendedStatus On

<Location "/server-status">
    SetHandler server-status
    Order deny,allow
    Deny from all
    Allow from localhost 192.168.105.170 
</Location>

####################################



Step 3: Now, check through browser using  http://localhost/server-status

Screenshots : 

HTTP Status Codes - Code A Site Resource

Thanks :-)