Mastering Automation: Streamlining Tasks with Bash Scripting

I never used to use bash scripts often but have found them increasingly more useful, I remember a friend of mine telling me about a less than competent co-worker of his that he would write bash scripts for just to take time off his hands when it came to the co-worker constantly asking for help because he couldn’t remember Linux commands one of the ones I remember specifically was related to flushing the firewall

#!/bin/bash
sudo iptables -nL -t raw -F

The script flushes all rules in the raw table of the iptables setup. This means it deletes all rules that might have been set in this table, effectively resetting it to its default state (no rules).

The reason I bring this up is that learning a scripting language Python, Bash, JavaScript etc. can increase general efficiency and time (also make it easier to use commands you might have forgotten or don’t want to type out entirely)

When using bash scripts it’s common that you will save them in a directory my personal scripts are in ‘scripts’ in my home directory for easy access, one script I use daily is connecting to VPN providers for different learning platforms I use

Connecting to VPN

#!/bin/bash

# Path to the OpenVPN binary
OPENVPN_PATH="/usr/local/Cellar/openvpn/2.6.8/sbin/openvpn"

# Path to your VPN configuration file
CONFIG_FILE="/Users/Trevor/Downloads/OPENvpn/us-academy-regular1.ovpn"

# Establish the VPN connection
sudo "$OPENVPN_PATH" --config "$CONFIG_FILE"

I have multiple different VPN scripts that save me time when connecting to these platforms instead of typing out, and remembering all of the paths / names of vpn profiles. Like shown below

sudo /usr/local/Cellar/openvpn/2.6.8/sbin/openvpn --config /Users/Trevor/Downloads/OPENvpn/us-academy-regular1.ovpn

I can just change my directory to my script directory ‘cd scripts‘ and then execute my bash script ./htbvpn.sh

One of the great things about bash scripting is that it is very simple to learn and to understand what the scripts do if you are already comfortable with your OS’s terminal / command line interface

Saving time with system administration and monitoring

Running NMAP scan to check devices connected to the network

#!/bin/bash

echo "Enter the subnet to scan (e.g., 192.168.1.0/24):"
read subnet

echo "Scanning for devices on the network $subnet..."
nmap -sn $subnet

echo "Network scan completed!"

Blocking a malicious domain

#!/bin/bash

echo "Enter the domain you wish to block:"
read domain

if grep -q "$domain" /etc/hosts; then
    echo "The domain $domain is already blocked."
else

    echo "127.0.0.1 $domain" | sudo tee -a /etc/hosts > /dev/null

    if grep -q "$domain" /etc/hosts; then
        echo "The domain $domain has been successfully blocked."
    else
        echo "Failed to block the domain $domain."
    fi
fi

Find top talkers (potential DDoS, Malicious Communication)

Another use is quickly executing complex / long commands in the shell like the example below using tcpdump, awk, cut, and sorting methods

#!/bin/bash

sudo tcpdump -nn -c 1000 ip | awk '{print $3}' | cut -d '.' -f 1-4 | sort | uniq -c | sort -nr | head -10

echo "Top talkers have been listed above."

The break down of this is pretty simple and shown in few lines compared to the previous due to the complexity of the tcpdump command comprising most of it.

Seen through these examples, mastering bash scripting can really simplify your workflow and free up your time for more complex and interesting tasks. Whether it’s flushing iptables, connecting to a VPN, scanning your network, or even blocking a malicious domain, each script serves as a mini toolkit at your disposal.

I hope this showing practical uses of bash can inspire you to start automating some of your own routine tasks. The beauty of scripting lies in its ability to make the complex simple and the tedious manageable.