🚀 Advanced Bash Scripting – Functions, Arguments, and Debugging

Introduction

Now that you’re familiar with basic Bash scripting, it’s time to take things up a notch with Advanced Bash Scripting

In this guide, we’ll cover:
✅ Using functions for better code organization
✅ Passing command-line arguments to scripts
✅ Debugging techniques to fix errors
✅ Best practices for writing clean scripts

By the end, you’ll be able to write modular, efficient, and error-free Bash scripts.

📌 1. Functions in Bash

Functions help organize code by grouping commands into reusable blocks.

Syntax of a Bash Function

function function_name() {
    # Code block
}

function_name() {
    # Code block
}

Example: Function to Greet Users

#!/bin/bash

greet_user() {
    echo "Hello, $1! Welcome to Bash scripting."
}

greet_user "Alice"

✅ Output:

Hello, Alice! Welcome to Bash scripting.

📌 $1 is the first argument passed to the function.

📌 2. Using Command-Line Arguments in Scripts

Scripts can accept user input via command-line arguments.

Example: Passing Arguments to a Script

#!/bin/bash

echo "Script Name: $0"
echo "First Argument: $1"
echo "Second Argument: $2"

Run the script with arguments:

./script.sh John 25

✅ Output:

Script Name: ./script.sh
First Argument: John
Second Argument: 25

📌 $0 → Script name
📌 $1, $2, $3 → First, second, third arguments

Handling Multiple Arguments with `$@` and `$#`

#!/bin/bash
echo "All Arguments: $@"
echo "Total Arguments: $#"

✅ $@ → All arguments
✅ $# → Number of arguments

📌 3. Conditional Statements in Bash

Use if, elif, and else to handle logic.

Example: Checking If a File Exists

#!/bin/bash
if [ -f "$1" ]; then
    echo "File $1 exists."
else
    echo "File $1 does not exist."
fi

Run the script:

./check_file.sh myfile.txt

📌 4. Loops in Advanced Bash Scripting

For Loop with File Processing

#!/bin/bash
for file in *.txt
do
   echo "Processing $file..."
done

While Loop with User Input

#!/bin/bash
while true
do
    echo "Enter a number (or type 'exit' to quit):"
    read input
    if [ "$input" == "exit" ]; then
        break
    fi
    echo "You entered: $input"
done

📌 5. Debugging Bash Scripts

Even experienced scripters encounter bugs! Here are ways to debug your script:

1️⃣ Enable Debug Mode (`-x` flag)

Run your script in debug mode to see every command executed:

bash -x script.sh

2️⃣ Add Debugging Statements (`set -x` and `set +x`)

Wrap parts of your script with set -x and set +x to debug specific sections.

#!/bin/bash

echo "Before debug mode"

set -x  # Start debugging
ls /invalid/path
set +x  # Stop debugging

echo "After debug mode"

3️⃣ Use the `trap` Command to Catch Errors

#!/bin/bash

trap 'echo "An error occurred on line $LINENO"; exit 1' ERR

ls /invalid/path

✅ Now, the script will display the line number where the error occurred!

📌 6. Best Practices for Writing Bash Scripts

✔ Use Comments (#): Explain your code for future reference.
✔ Use Meaningful Variable Names: Avoid generic names like var1, var2.
✔ Check for Errors: Use [ -f ] for files, [ -d ] for directories.
✔ Make Scripts Executable: Use chmod +x script.sh.
✔ Format Output Clearly: Use echo -e for colored output.

Example:

echo -e "\e[32mSuccess!\e[0m"  # Prints green text

🎯 Final Thoughts

Now you know how to write functions, pass arguments, debug scripts, and follow best practices.

💡 Next Blog: Linux Shell Scripting – Automate Admin Tasks Like a Pro

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