Linux Bash Scripting Guide

Linux Bash Scripting Guide

Complete beginner-friendly guide to Bash scripting on Linux, covering Arch Linux, CachyOS, and other distributions including script creation, variables, loops, conditionals, and automation.

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Table of Contents

1. Understanding Bash Scripting
2. Creating Scripts
3. Variables
4. Conditionals
5. Loops
6. Functions
7. Input/Output
8. Troubleshooting

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Understanding Bash Scripting

What is Bash Scripting?

Bash scripting automates tasks using shell commands.

Uses:

• Automation: Automate repetitive tasks
• System administration: Manage systems
• File processing: Process files in bulk
• Backup scripts: Create automated backups

Benefits:

• Time saving: Automate manual tasks
• Consistency: Same tasks run the same way
• Error reduction: Fewer manual errors

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Creating Scripts

First Script

Create script:

# Create script file
vim myscript.sh

Add:

#!/bin/bash
echo "Hello, World!"

Make executable:

# Make executable
chmod +x myscript.sh

# Run script
./myscript.sh

Shebang

Script header:

#!/bin/bash
# This tells system to use bash

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Variables

Basic Variables

Set variables:

#!/bin/bash
NAME="John"
AGE=25

echo "Name: $NAME"
echo "Age: $AGE"

Environment Variables

Use environment variables:

#!/bin/bash
echo "User: $USER"
echo "Home: $HOME"
echo "Path: $PATH"

Command Substitution

Store command output:

#!/bin/bash
DATE=$(date)
FILES=$(ls)

echo "Date: $DATE"
echo "Files: $FILES"

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Conditionals

If Statements

Basic if:

#!/bin/bash
if [ "$1" == "hello" ]; then
    echo "Hello!"
fi

If-Else

If-else:

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

Case Statements

Case:

#!/bin/bash
case "$1" in
    start)
        echo "Starting..."
        ;;
    stop)
        echo "Stopping..."
        ;;
    *)
        echo "Usage: $0 {start|stop}"
        ;;
esac

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Loops

For Loop

For loop:

#!/bin/bash
for i in 1 2 3 4 5; do
    echo "Number: $i"
done

Loop through files:

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

While Loop

While loop:

#!/bin/bash
count=1
while [ $count -le 5 ]; do
    echo "Count: $count"
    count=$((count + 1))
done

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Functions

Define Functions

Create function:

#!/bin/bash
greet() {
    echo "Hello, $1!"
}

greet "John"

Function with Return

Return value:

#!/bin/bash
add() {
    result=$(( $1 + $2 ))
    echo $result
}

sum=$(add 5 3)
echo "Sum: $sum"

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Input/Output

Read Input

Get user input:

#!/bin/bash
echo "Enter your name:"
read name
echo "Hello, $name!"

Command Line Arguments

Use arguments:

#!/bin/bash
echo "Script: $0"
echo "First argument: $1"
echo "Second argument: $2"
echo "All arguments: $@"

Redirect Output

Save output:

#!/bin/bash
# Redirect to file
echo "Hello" > output.txt

# Append to file
echo "World" >> output.txt

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Troubleshooting

Script Not Running

Check permissions:

# Make executable
chmod +x script.sh

# Check shebang
head -1 script.sh

Debug Script

Debug mode:

# Run with debug
bash -x script.sh

# Check syntax
bash -n script.sh

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Summary

This guide covered Bash scripting basics, variables, conditionals, loops, and functions for Arch Linux, CachyOS, and other distributions.

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Next Steps

• Shell Configuration - Shell setup
• cron Guide - Schedule scripts
• systemd Timers Guide - Modern scheduling
• Bash Documentation: man bash

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This guide covers Arch Linux, CachyOS, and other Linux distributions. For distribution-specific details, refer to your distribution's documentation.