Port scanning basics in Bash Scripting - Mini Project: Build & Apply

Port scanning basics

📖 Scenario: You are a network technician who needs to check which ports are open on a local server to ensure the services are running correctly.

🎯 Goal: Build a simple Bash script that scans a range of ports on a given IP address and reports which ports are open.

📋 What You'll Learn

Create a variable holding the target IP address

Create a variable holding the start and end port numbers

Use a loop to scan each port in the range

Check if the port is open using Bash built-in tools

Print the list of open ports

💡 Why This Matters

🌍 Real World

Network administrators often need to check which ports are open on servers to troubleshoot connectivity or security issues.

💼 Career

Basic port scanning skills help in network monitoring, security auditing, and system administration roles.

1

Set the target IP address

Create a variable called target_ip and set it to the string "127.0.0.1".

Bash Scripting

# Create a variable called target_ip and set it to "127.0.0.1"
# Your code here

Need a hint?

Use variable_name="value" syntax to create a variable in Bash.

2

Set the port range to scan

Create two variables called start_port and end_port and set them to 75 and 85 respectively.

Bash Scripting

target_ip="127.0.0.1"
# Create variables start_port and end_port with values 75 and 85
# Your code here

Need a hint?

Assign numbers to variables without quotes in Bash.

3

Scan ports in the range

Use a for loop with variable port to iterate from start_port to end_port. Inside the loop, use timeout 1 bash -c " to try connecting to $target_ip on $port with /dev/tcp. If the connection succeeds, add the port number to a variable called open_ports separated by spaces.

Bash Scripting

target_ip="127.0.0.1"
start_port=75
end_port=85
# Use a for loop from start_port to end_port
# Check if port is open using timeout and /dev/tcp
# Add open ports to open_ports variable
# Your code here

Need a hint?

Use seq to generate numbers and timeout 1 bash -c "echo > /dev/tcp/$target_ip/$port" to test ports.

4

Print the open ports

Print the text "Open ports:" followed by the value of the variable open_ports.

Bash Scripting

target_ip="127.0.0.1"
start_port=75
end_port=85
open_ports=""
for port in $(seq $start_port $end_port); do
  if timeout 1 bash -c "echo > /dev/tcp/$target_ip/$port" 2>/dev/null; then
    open_ports+="$port "
  fi
done
# Print "Open ports:" and the open_ports variable
# Your code here

Need a hint?

Use printf or echo to display the open ports.