Script Fundamentals

Welcome to Interactive Bash Scripting! This course builds on the Linux Command Line Basics course and teaches you how to write powerful automation scripts.

Prerequisites

This course assumes you've completed the Linux Command Line Basics course or have equivalent knowledge of:

• Basic terminal navigation (cd, ls, pwd)
• File operations (touch, mkdir, cp, mv, rm)
• Viewing files (cat, less, head, tail)
• File permissions (chmod)
• Pipes and redirection

What is Bash Scripting?

Bash scripting is the art of combining shell commands into reusable programs. Instead of typing commands one by one, you write them in a file that can be executed repeatedly.

Why learn bash scripting?

• Automation: Automate repetitive tasks
• Efficiency: Run complex operations with a single command
• DevOps: Essential for system administration and CI/CD
• Portability: Works on any Unix/Linux system

Your First Look at a Script

Let's examine a simple script structure:

#!/bin/bash
# This is a comment describing the script
# Author: Your Name

# Define a variable
GREETING="Hello, World!"

# Display the greeting
echo "$GREETING"

# Exit successfully
exit 0

Script Components

Every bash script has these key components:

Component	Purpose	Example
Shebang	Tells system which interpreter to use	#!/bin/bash
Comments	Document your code	# This does X
Variables	Store data	NAME="value"
Commands	Perform actions	echo, cp, mkdir
Exit code	Indicate success/failure	exit 0

Script vs Interactive Shell

When you type commands in the terminal, you're using an interactive shell. Scripts are non-interactive - they run without user intervention (unless designed to prompt for input).

Key differences:

# Interactive shell - you see prompts, can use history
$ ls
$ cd projects

# Script - runs all at once, no prompts
#!/bin/bash
ls
cd projects

Exercise: Explore Existing Scripts

Look at the backup script to understand script structure:

Script File Conventions

Follow these naming conventions:

• Use .sh extension: backup.sh, deploy.sh
• Use descriptive names: cleanup_logs.sh not script1.sh
• Use underscores or hyphens: my-script.sh or my_script.sh
• Avoid spaces in filenames

Script File Locations

Common locations for scripts:

Location	Purpose
~/bin/	Personal scripts
/usr/local/bin/	System-wide custom scripts
./scripts/	Project-specific scripts
/etc/cron.d/	Scheduled scripts

Creating Your First Script File

Let's create a simple script:

# Step 1: Create the file
touch hello.sh

# Step 2: Add content (we'll learn better ways)
echo '#!/bin/bash' > hello.sh
echo 'echo "Hello from my first script!"' >> hello.sh

# Step 3: View it
cat hello.sh

Key Takeaways

• Bash scripts are text files containing shell commands
• Scripts automate repetitive tasks and complex operations
• Every script should start with a shebang (#!/bin/bash)
• Use comments to document your code
• Follow naming conventions: descriptive names with .sh extension
• This course builds on Linux Command Line Basics knowledge