Scripting

1. Overview

What it is: Automating operational tasks with Bash, Python, Go, etc.

When to use: Glue between tools; one-off safe automation; CI steps.

When NOT to: Replacing real applications; untested scripts that mutate prod without dry-run.

2. Concepts

• Idempotency — safe re-run
• Exit codes — 0 success
• set -euo pipefail (Bash discipline)
• Quoting — prevent word-splitting
• Dry-run flags
• Structured logging
• Secrets via env/store — never argv if avoidable
• Python click/typer for CLIs

3. Architecture

graph LR
  Trigger[CI / Cron / Human] --> Script
  Script --> APIs[Cloud / K8s APIs]
  Script --> Logs
  Script --> Exit[Exit Code]

4. Production Best Practices

• ShellCheck + set -euo pipefail
• Prefer Python for complex logic
• --dry-run for destructive ops
• Explicit timeouts on network calls
• Version scripts in git; code review
• Minimal output of secrets

5. Common Mistakes

Mistake	Fix
Unquoted $var	Always quote
Ignoring exit codes in pipes	pipefail
curl without -f	Fail on HTTP errors
Parsing kubectl plain text	-o json + jq

6. Debugging Guide

bash -x ./script.sh
shellcheck ./script.sh
python -m pdb tool.py

7. Security

• Don't pass secrets on command line (visible in ps)
• Validate inputs; never eval user input
• Least privilege credentials for script roles

8. Performance

• Avoid O(n) API calls in loops — batch
• Parallelism with care (xargs -P) and rate limits

9. Real Production Example

Python typer CLI for "drain node safely": cordon → drain → wait PDB → notify Slack; --dry-run default in non-prod; unit-tested helpers.

10. Interview Questions

Beginner: What does set -e do?

Intermediate: Why quote variables?

Senior: Design safe automation platform for prod changes.

11. Checklist

• ShellCheck/linters
• Dry-run for destructive
• Timeouts + retries bounded
• Secrets safe
• Exit codes meaningful

12. Cheat Sheet

#!/usr/bin/env bash
set -euo pipefail
ROOT="$(cd "$(dirname "$0")" && pwd)"
log() { printf '%s %s\n' "$(date -Is)" "$*"; }

import subprocess, sys
subprocess.run(["kubectl", "get", "pods", "-o", "json"], check=True)

Related Skills

• linux
• cicd
• troubleshooting
• git

---

Author & maintainer: Shanmukha Kumar Karra
Created and maintained as part of AgentOps Kit.