- By now, your scripts deploy apps, manage servers, and clean logs.
- But what happens when things go wrong?
- Welcome to Debugging & Logging, where we make your scripts smarter and traceable like a pro DevOps engineer! 🕵️♂️
📑 Table of Contents
- Debugging with set -x
- Using trap to Handle Failures
- Exit Codes & Error Messages
- Logging with Syslog & Files
- Real Middleware Examples
- Summary
🐞 1️⃣ Debugging with set -x
set -x shows every command the script executes — perfect for troubleshooting silent errors.
#!/bin/bash
set -x # enable debugging
echo "Starting deployment..."
mkdir /opt/app/deploy
cp /tmp/app.war /opt/app/deploy/
set +x # disable debugging
echo "Deployment finished!"
💬 Output:
+ echo "Starting deployment..."Starting deployment...
+ mkdir /opt/app/deploy
+ cp /tmp/app.war /opt/app/deploy/
+ echo "Deployment finished!"
Deployment finished!
💡 Use
bash -x script.sh to debug a script without editing it.🪤 2️⃣ Using trap to Handle Failures
The trap command catches unexpected exits (Ctrl+C, errors) and executes custom recovery code. Perfect for cleanup or service restarts.
#!/bin/bash
trap 'echo "⚠️ Script interrupted! Cleaning up..."; rm -f /tmp/tempfile' EXIT
echo "Creating temporary file..."
touch /tmp/tempfile
echo "Simulating work..."
sleep 3
exit 1 # simulate failure
💬 Output:
Creating temporary file...Simulating work...
⚠️ Script interrupted! Cleaning up...
💡 Always trap
EXIT or ERR to prevent orphan temp files or hanging processes.🚪 3️⃣ Exit Codes & Error Messages
Every command returns an exit code — 0 means success, non-zero means failure.
#!/bin/bash
cp /tmp/app.war /opt/app/deploy/
if [ $? -ne 0 ]; then
echo "❌ Copy failed! Check file path or permissions."
exit 1
else
echo "✅ Copy successful!"
fi
💬 Output:
❌ Copy failed! Check file path or permissions.or
✅ Copy successful!
Use
echo $? after any command to view its exit code.🧾 4️⃣ Logging with Syslog & Custom Files
Example 1: Using logger Command
#!/bin/bash
logger "Starting Middleware backup..."
tar -czf /tmp/backup.tar.gz /opt/middleware/ || logger "Backup failed!"
logger "Middleware backup completed!"
💬 Syslog Output (in /var/log/syslog):
Nov 1 02:15:00 server logger: Starting Middleware backup...Nov 1 02:15:03 server logger: Middleware backup completed!
Example 2: Redirecting Logs to a File
#!/bin/bash
exec >> /opt/logs/deploy.log 2>&1
echo "[$(date)] Starting deployment..."
echo "[$(date)] Copying WAR..."
cp /tmp/app.war /opt/tomcat/webapps/
echo "[$(date)] Deployment done ✅"
💬 deploy.log Content:
[Sat Nov 1 02:20:00 2025] Starting deployment...[Sat Nov 1 02:20:01 2025] Copying WAR...
[Sat Nov 1 02:20:02 2025] Deployment done ✅
⚙️ 5️⃣ Real Middleware & DevOps Examples
Example 1: Jenkins Job Failure Recovery
#!/bin/bash
set -e
trap 'echo "🚨 Jenkins build failed, restarting service..."; systemctl restart jenkins' ERR
curl -s -X POST "http://localhost:8080/job/myjob/build" || false
echo "✅ Jenkins job triggered successfully!"
💬 Output:
🚨 Jenkins build failed, restarting service...✅ Jenkins job triggered successfully!
Example 2: Tomcat Log Watcher with Debug Info
#!/bin/bash
set -x
tail -Fn0 /opt/tomcat/logs/catalina.out | \
while read line; do
echo "$line" | grep "ERROR" &>/dev/null && echo "🔥 Found error: $line" >> /opt/logs/tomcat_error.log
done
💬 Output:
[DEBUG] + grep "ERROR" catalina.out🔥 Found error: Database connection timeout
Example 3: NGINX Health Check with Logging
#!/bin/bash
while true; do
if ! systemctl is-active nginx >/dev/null; then
echo "$(date): 🚨 NGINX is down, restarting..." >> /var/log/nginx_monitor.log
systemctl restart nginx
fi
sleep 10
done
💬 Log Output:
Sat Nov 1 03:00:00 2025: 🚨 NGINX is down, restarting...🏁 Summary
- set -x → Debug command execution flow.
- trap → Catch exits & clean up automatically.
- exit codes → Detect and handle failures gracefully.
- logger → Send messages to syslog or custom logs.
- 💡 Always include logging in production-ready scripts for audit and rollback.
