Advanced Shell Scripting

Functions, arrays, and error handling. Build production-grade security tools.

Functions

Functions make scripts modular, reusable, and maintainable. Define once, call anywhere.

# Define a function
scan_host() {
    local host=$1
    echo "Scanning $host..."
    for port in 22 80 443; do
        nc -z -w1 $host $port 2>/dev/null && \
            echo "  [OPEN] $port"
    done
}

# Call the function
scan_host "192.168.1.1"
scan_host "192.168.1.2"

Arrays

# Declare an array
targets=("192.168.1.1" "192.168.1.2" "192.168.1.3")

# Loop through array
for ip in "${targets[@]}"; do
    scan_host "$ip"
done

# Array length: ${#targets[@]}
# Single element: ${targets[0]}

Error Handling

set -e

Exit immediately if any command fails. Prevents cascading errors.

set -u

Treat unset variables as errors. Catches typos in variable names.

trap

Catch signals and cleanup. trap cleanup EXIT

#!/bin/bash
set -euo pipefail  # Strict mode

cleanup() {
    echo "Cleaning up temp files..."
    rm -f /tmp/scan_*.tmp
}
trap cleanup EXIT

# Script continues...

LAB: Function Playground

Build a multi-target scanner using functions and arrays. Your script should scan multiple hosts!

☐Define a function

☐Create an array of targets

☐Loop through the array

☐Call your function for each target

scanner.sh

⬤Output

Ready to run your script... Build a scanner that: 1. Defines a scan_target() function 2. Creates a targets=() array 3. Loops through with for...in 4. Calls scan_target for each

FUNCTION LAB COMPLETE!

You've built a modular, reusable scanner tool!

Ready to Test Your Skills?

Take the Quiz → Back to Script House

Completing CLH-007 to CLH-009 earns: CLI Specialist