Dry-Run and Diff Modes

Dry-Run and Diff Modes

This lesson deepens Shell Scripting & Automation using the same subject areas emphasized by official documentation: GNU Bash manual topics: strict mode, expansion, quoting, traps, functions, awk, sed, jq, idempotency and timers. The goal is to turn Dry-Run and Diff Modes into a production skill: you should know the concept, the configuration surface, the safety controls, the operational checks, and the rollback path.

Documentation Coverage

• Core terms and object model for this topic.
• Configuration options, defaults, and lifecycle behavior from the docs.
• Security, reliability, and ownership boundaries.
• Validation steps before and after the change.
• Common failure modes and diagnostic signals.

Production Implementation Flow

1. Define the source of truth: Git, configuration, API, state file, or control plane.
2. Design the safest repeatable workflow, including dry-run or plan output where possible.
3. Attach CI/CD, policy, security, and peer-review gates.
4. Observe metrics, logs, events, or traces after the change.
5. Document rollback, escalation owner, and evidence for the change record.

set -euo pipefail
systemctl --failed
journalctl -p warning --since '30 minutes ago'
find /var/log -type f -mtime -1 -size +10M

Mastery Standard

You understand Dry-Run and Diff Modes when you can explain it, configure it, test it, monitor it, and recover it under incident pressure without relying on undocumented manual steps.