Shell Networking Skill Skill

Shell Networking Skill

Master networking operations from the command line

Learning Objectives

After completing this skill, you will be able to:

[ ] Make HTTP requests with curl
[ ] Use SSH for remote operations
[ ] Check ports and connections
[ ] Debug network issues
[ ] Transfer files securely

Prerequisites

Bash basics
Basic networking concepts
Understanding of HTTP

Core Concepts

1. Curl Essentials

# Basic requests
curl https://api.example.com            # GET
curl -X POST https://api.example.com    # POST
curl -o file.zip https://example.com/f  # Download

# Headers and data
curl -H "Authorization: Bearer $TOKEN" \
     -H "Content-Type: application/json" \
     -d '{"key":"value"}' \
     https://api.example.com

# Common options
curl -v url        # Verbose
curl -s url        # Silent
curl -L url        # Follow redirects
curl -k url        # Skip SSL verify
curl -w "%{http_code}" -o /dev/null -s url

2. SSH Operations

# Connect
ssh user@host
ssh -p 2222 user@host
ssh -i ~/.ssh/key.pem user@host

# File transfer
scp file.txt user@host:/path/
scp -r dir/ user@host:/path/
scp user@host:/path/file.txt ./

# Tunnels
ssh -L 8080:localhost:80 user@host
ssh -D 1080 user@host     # SOCKS proxy

3. Port Checking

# List listening ports
ss -tlnp                  # TCP
ss -ulnp                  # UDP
netstat -tlnp             # Alternative

# Check specific port
nc -zv host 80            # Port check
lsof -i :8080             # What's using port

# Scan ports
nmap -sT host             # TCP scan
nmap -p 80,443 host       # Specific ports

4. DNS Operations

# DNS lookup
dig example.com
dig +short example.com    # IP only
dig example.com MX        # MX records
dig @8.8.8.8 example.com  # Specific DNS

# Alternatives
host example.com
nslookup example.com

Common Patterns

API Request with Error Handling

response=$(curl -s -w "\n%{http_code}" \
    -H "Authorization: Bearer $TOKEN" \
    "https://api.example.com/data")
http_code=$(echo "$response" | tail -1)
body=$(echo "$response" | sed '$d')

if [[ "$http_code" != "200" ]]; then
    echo "Error: HTTP $http_code"
    exit 1
fi

Wait for Port

wait_for_port() {
    local host="$1" port="$2" timeout="${3:-30}"
    for ((i=0; i<timeout; i++)); do
        if nc -z "$host" "$port" 2>/dev/null; then
            return 0
        fi
        sleep 1
    done
    return 1
}

SSH Config

# ~/.ssh/config
Host myserver
    HostName 192.168.1.100
    User admin
    Port 2222
    IdentityFile ~/.ssh/mykey

Anti-Patterns

| Don't | Do | Why | |-------|-----|-----| | curl \| bash | Download, inspect, run | Security risk | | Store passwords | Use SSH keys | More secure | | Skip SSL verify | Fix certificates | Security |

Practice Exercises

API Client: Script to interact with REST API
Health Checker: Check if services are up
SSH Automation: Run commands on multiple hosts
Port Scanner: Simple port availability checker

Troubleshooting

Common Errors

| Error | Cause | Fix | |-------|-------|-----| | Connection refused | Service down | Check if running | | Connection timed out | Firewall/routing | Check network | | Name not resolved | DNS issue | Check DNS | | Permission denied (publickey) | SSH key | Check authorized_keys |

Debug Techniques

# Test connectivity
ping -c 2 host
traceroute host

# Debug curl
curl -v https://example.com

# Debug SSH
ssh -vvv user@host

Security Guidelines

Use SSH keys instead of passwords
Verify SSL certificates in production
Don't store secrets in scripts
Use environment variables for credentials
Audit SSH access regularly

Agent Skills: Shell Networking Skill

Skill Files