System Tools & CLI Reference

Overview

This skill provides patterns and best practices for command-line infrastructure management, development workflows, and system administration.

Reference files (load when needed):

•references/cli-reference.md - Complete command reference for all tools
•references/advanced.md - Complex workflows, scripting patterns, automation
•references/troubleshooting.md - Error messages, debugging strategies

Helper scripts in scripts/:

•retry.sh - Retry commands with exponential backoff
•health-check.sh - Service health monitoring
•backup-postgres.sh - PostgreSQL backup with rotation

Quick Reference

Domain	Tools	When to Use
Version Control	`git`, `gh`	Code management, PRs, issues
Cloud CLIs	`aws`, `gcloud`, `az`, `doctl`	Infrastructure provisioning
Containers	`docker`, `kubectl`, `helm`	Container orchestration
Remote Access	`ssh`, `scp`, `rsync`, `curl`	File transfer, API calls
Databases	`psql`, `mysql`, `redis-cli`	Database queries
Data Processing	`jq`, `yq`, `grep`, `awk`	Transform structured data

Core Workflows

Git & GitHub

bash

# Clone and branch
git clone https://github.com/owner/repo.git && cd repo
git checkout -b feature/new-feature

# Stage, commit, push
git add -p                          # Interactive staging
git commit -m "type: description"
git push origin feature/new-feature

# Pull request workflow
gh pr create --fill
gh pr list
gh pr checkout 123
gh pr merge 123 --squash --delete-branch

Critical rules:

•Never force push to shared branches (main, develop)
•Use --force-with-lease instead of --force

Docker

bash

# Build and run
docker build -t myapp:v1 .
docker run -d --name web -p 8080:80 nginx
docker run -it --rm ubuntu:22.04 bash

# Inspect and debug
docker ps -a
docker logs -f container_name
docker exec -it container_name bash

# Cleanup
docker system prune -a --volumes

Critical rules:

•Use specific image tags, never latest in production
•Set resource limits in production

Kubernetes

bash

# Context
kubectl config get-contexts
kubectl config use-context my-cluster

# Resources
kubectl get pods -o wide
kubectl describe pod pod-name
kubectl logs -f pod-name

# Apply and scale
kubectl apply -f manifest.yaml
kubectl scale deployment nginx --replicas=3
kubectl rollout undo deployment nginx

# Debug
kubectl get events --sort-by='.lastTimestamp'
kubectl run debug --image=busybox -it --rm -- sh

SSH & File Transfer

bash

# Connect
ssh user@hostname
ssh -i ~/.ssh/mykey.pem user@hostname

# Port forwarding
ssh -L 8080:localhost:80 user@server   # Local forward
ssh -J jumphost user@target            # Jump through bastion

# File transfer (prefer rsync for large transfers)
rsync -avz --progress ./src/ user@host:/dst/
rsync -avz --delete ./src/ dst/        # Mirror

Database Queries

bash

# PostgreSQL
psql -h localhost -U postgres -d dbname
psql -c "SELECT * FROM users LIMIT 10" -d dbname
pg_dump -Fc dbname > backup.dump

# MySQL
mysql -h localhost -u root -p dbname

# Redis (never use KEYS * in production)
redis-cli
SCAN 0 MATCH "user:*" COUNT 100

Data Processing with jq

bash

# Extract and filter
jq '.users[].name' data.json
jq '.users[] | select(.age > 30)' data.json

# Transform
jq '{name: .full_name, email: .contact.email}' data.json
jq '.items | sort_by(.price) | reverse' data.json

# Raw output
jq -r '.name' data.json

Cloud CLIs

bash

# AWS
aws configure
aws s3 sync ./local s3://bucket/dir
aws ec2 describe-instances --query 'Reservations[].Instances[].{ID:InstanceId,State:State.Name}'

# GCP
gcloud auth login
gcloud config set project PROJECT_ID
gcloud compute instances list

# DigitalOcean
doctl auth init
doctl compute droplet list

Critical rules:

•Never commit credentials to version control
•Use IAM roles/service accounts over static credentials

Helper Scripts Usage

retry.sh - Exponential Backoff

bash

# Retry a flaky command up to 5 times
scripts/retry.sh 5 curl -f https://api.example.com/health

# With custom delays
scripts/retry.sh -d 2 -m 30 -v 3 docker pull nginx:latest

health-check.sh - Service Monitoring

bash

# Run default checks
scripts/health-check.sh

# From config file
scripts/health-check.sh checks.conf

# Config format:
# http:https://api.example.com/health:200
# tcp:localhost:5432
# process:nginx
# disk:/:80

backup-postgres.sh - Database Backup

bash

# Basic backup
scripts/backup-postgres.sh mydb /backups

# With options
scripts/backup-postgres.sh -h db.example.com -U admin -k 30 mydb /backups

Common Patterns

API Testing

bash

curl -X POST https://api.example.com/data \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $TOKEN" \
  -d '{"key": "value"}' | jq '.'

Log Analysis

bash

# Find errors with context
grep -E "error|exception" app.log | tail -50

# Count by type
grep -oE "Error: [^:]*" app.log | sort | uniq -c | sort -rn

Quick Backup

bash

# PostgreSQL
pg_dump -Fc dbname > backup_$(date +%Y%m%d).dump

# Sync to remote
rsync -avz /data/ backup-server:/backups/

When to Load References

Load references/cli-reference.md when:

•Need complete command options for a specific tool
•Looking up less common flags or features
•Working with tools not covered in quick reference

Load references/advanced.md when:

•Writing shell scripts with error handling
•Setting up CI/CD pipelines
•Implementing infrastructure as code
•Working with multi-cloud environments
•Need security hardening patterns

Load references/troubleshooting.md when:

•Encountering error messages
•Debugging connectivity issues
•Diagnosing performance problems
•Container or Kubernetes pods not starting

Dependencies

Core tools typically pre-installed: git, ssh, curl, grep, awk

Install via apt:

bash

apt install jq postgresql-client mysql-client redis-tools docker.io htop

Cloud CLIs:

bash

# AWS
curl "https://awscli.amazonaws.com/awscli-exe-linux-x86_64.zip" -o "awscliv2.zip"
unzip awscliv2.zip && sudo ./aws/install

# GitHub CLI
apt install gh