Blog 15 Leveling Up Shell: Idempotent Scripts, Deployments & Log Cleanup

🖥️Idempotency, Deployment & Log Cleanup in Shell Scripting

Welcome back to the journey 🚀 In blog 14 , we learned about functions and loops. Now in blog 15, we step into real-world server automation concepts.

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🔁 1️⃣ What is Idempotency?

Idempotent = Same result no matter how many times you run it

id ec2-user &>/dev/null || useradd ec2-user
  

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🌐 2️⃣ Idempotency in HTTP Methods

Method	Idempotent?	Why
GET	✅	Only reads data
PUT	✅	Updates same resource
DELETE	✅ (mostly)	Deleting again gives “not found”
POST	❌	Creates new data each time

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🚀 3️⃣ Deployment Steps (Real Server)

rm -rf /app/*
git clone repo-url /app
cd /app && npm install
systemctl restart myapp
  

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📂 4️⃣ Log Management in Linux

find /var/log/myapp -name "*.log" -mtime +14 -delete
  

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📦 5️⃣ Archiving Old Logs

mkdir -p /archive/logs
find /var/log/myapp -name "*.log" -mtime +14 -exec mv {} /archive/logs \;
  

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⏳ 6️⃣ Creating Old Files for Testing

touch -d "20 days ago" test.log
  

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🔄 7️⃣ While Loop – Read File Line by Line

FILE=temp.txt

while read line
do
  echo "Processing $line"
done < $FILE
  

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🧩 8️⃣ Why Shell Scripts Are Not Naturally Idempotent

Running scripts repeatedly can reinstall packages, duplicate users, or overwrite files. We must add logic to make scripts idempotent.

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📦 9️⃣ NPM Warnings (Informational)

Sometimes npm install shows warnings about optional dependencies. These are not errors and don’t affect core functionality.

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🧠 🔟 Final Takeaway

we moves you from writing scripts to building reliable server automation.

• Idempotency mindset
• Safe deployments
• Log rotation
• File handling with loops

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© Kalyan – DevSecOps Journey