Mastering Linux Bash Scripting: Part 1 - The Fundamentals

If you work with Linux, whether as a System Administrator, a DevOps engineer, or a Cybersecurity analyst, the terminal is your home. While you can type commands one by one, the real power of Linux unlocks when you start scripting.

This is Part 1 of our Bash Scripting roadmap. In this article, we will cover the absolute basics: why we use it, how to create your first script, and how to handle data using variables.

Table of Contents

1. Why Learn Bash?
2. The Shebang & Your First Script
3. Variables in Bash
4. Data Types: Strings vs. Numbers
5. Next Steps

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1. Why Learn Bash?

Bash (Bourne Again SHell) is the default command-line interpreter for most Linux distributions. Writing a script is essentially saving a list of commands to a file so the computer can execute them for you.

Here is why you need to learn it:

• Automation: If you have to do a task more than twice, automate it. Bash is perfect for daily backups, system updates, or log cleaning.
• Universality: Bash is pre-installed on almost every Linux server in the world. You don’t need to install Python or Java to get things done.
• Speed: For managing files and system processes, Bash is faster and more direct than writing a high-level program.

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2. The Shebang & Your First Script

Before we talk about variables, we need to know how to make a file “executable.”

Every Bash script starts with a specific line called the Shebang. This tells the system which interpreter to use to run the code.

The Syntax

Create a file named hello.sh.

#!/bin/bash

# This is a comment. The system ignores lines starting with #
echo "Hello, World!"

How to Run It

By default, Linux files are not executable for security reasons. You must grant permission first.

1. Make it executable:

   chmod +x hello.sh
   

2. Run the script:

   ./hello.sh
   

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3. Variables in Bash

Variables are containers for storing data. Unlike languages like C++ or Java, Bash is very flexible with variables, but it is strict about syntax.

Declaring Variables

The Golden Rule: There must be NO SPACES around the equal sign =.

• ❌ name = "John" (This will fail)
• ✅ name="John" (This works)

Accessing Variables

To use the value stored in a variable, you must put a $ sign in front of it.

Example Script: user_info.sh

#!/bin/bash

# Defining variables
username="CyberUser"
role="Penetration Tester"
directory="/home/cyberuser/tools"

# Using the variables
echo "The user $username is working as a $role."
echo "Their tools are located in: $directory"

Output:

The user CyberUser is working as a Penetration Tester. Their tools are located in: /home/cyberuser/tools

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4. Data Types: Strings vs. Numbers

Bash is technically a “typeless” or “loosely typed” language. It essentially treats everything as a string (text) unless you force it to do math.

1. Strings

Strings are just text. You should generally wrap them in quotes.

• Double Quotes (""): Allow variables to be expanded.
• Single Quotes (''): Treat everything literally (variables won’t work).

Example:

name="Alice"

echo "Hello, $name"  # Output: Hello, Alice
echo 'Hello, $name'  # Output: Hello, $name (Literal string)

2. Integers (Numbers)

Because Bash treats everything as text, 1 + 1 is just the text “1 + 1”. To do math, we need special syntax.

We use double parentheses (( ... )) for arithmetic.

Example Script: math_test.sh

#!/bin/bash

num1=10
num2=5

# Incorrect way (will just print the text)
echo $num1 + $num2 

# Correct way (performs the math)
sum=$(( num1 + num2 ))
echo "The sum is: $sum"

# You can also do subtraction, multiplication, etc.
echo "Multiplication: $(( num1 * num2 ))"

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5. Next Steps

Congratulations! You’ve taken the first step. You now understand how to create a script, set permissions, store data in variables, and perform basic math.

In Part 2, we will make our scripts intelligent. We will cover:

• User Input: Asking the user for data.
• Logic: Using if, else, and elif statements.
• Loops: Repeating tasks automatically.