Debian Bash Basics

Introduction

The Bash shell (Bourne Again SHell) is the default command-line interface in Debian Linux. It provides a powerful way to interact with your system, execute commands, and automate tasks. Whether you're a system administrator, developer, or Linux enthusiast, understanding Bash basics is essential for effective use of Debian systems.

In this tutorial, we'll explore the fundamental concepts of Bash in Debian, from navigating the filesystem to executing basic commands and understanding shell scripting principles. By the end of this guide, you'll have a solid foundation to build upon for more advanced shell scripting techniques.

Getting Started with the Terminal

Opening the Terminal

In Debian, you can open a terminal in several ways:

• Keyboard shortcut: Ctrl+Alt+T
• From the application menu: Look for "Terminal" or "Konsole" depending on your desktop environment
• Right-click on the desktop: Some desktop environments offer a "Open Terminal" option

When you open a terminal, you'll see a prompt that typically looks like this:

bash

username@hostname:~$

This prompt provides important information:

• username: Your current user
• hostname: The name of your computer
• ~: Your current directory (~ represents your home directory)
• $: Indicates you're logged in as a regular user (a # would indicate root privileges)

Basic Navigation Commands

Checking Your Current Location

To know where you are in the filesystem:

bash

pwd

Example output:

/home/username

Listing Files and Directories

List files and directories in your current location:

bash

ls

For more detailed information:

bash

ls -l

Example output:

total 32
drwxr-xr-x 2 username username 4096 Mar 13 15:30 Documents
drwxr-xr-x 2 username username 4096 Mar 13 15:30 Downloads
drwxr-xr-x 2 username username 4096 Mar 13 15:30 Music
drwxr-xr-x 2 username username 4096 Mar 13 15:30 Pictures
drwxr-xr-x 2 username username 4096 Mar 13 15:30 Public
drwxr-xr-x 2 username username 4096 Mar 13 15:30 Templates
drwxr-xr-x 2 username username 4096 Mar 13 15:30 Videos
-rw-r--r-- 1 username username  220 Mar 13 15:30 .bash_logout

To show hidden files (files that start with a dot):

bash

ls -a

Combining options:

bash

ls -la

Changing Directories

Move to a different directory:

bash

cd Documents

Go back to the parent directory:

bash

cd ..

Go to your home directory:

bash

cd
# or
cd ~

Go to the root directory:

bash

cd /

Navigate to an absolute path:

bash

cd /var/log

File Operations

Creating Files and Directories

Create a new directory:

bash

mkdir my_folder

Create nested directories:

bash

mkdir -p parent/child/grandchild

Create an empty file:

bash

touch myfile.txt

Copying Files and Directories

Copy a file:

bash

cp source.txt destination.txt

Copy a file to another directory:

bash

cp myfile.txt my_folder/

Copy a directory and its contents:

bash

cp -r source_directory destination_directory

Moving and Renaming

Move a file:

bash

mv source.txt destination.txt

Rename a file:

bash

mv oldname.txt newname.txt

Move a file to a directory:

bash

mv myfile.txt my_folder/

Deleting Files and Directories

Remove a file:

bash

rm myfile.txt

Remove an empty directory:

bash

rmdir my_folder

Remove a directory and all its contents:

bash

rm -r my_folder

⚠️ Warning: Be extremely careful with rm -r and never use rm -rf / as it will delete your entire system without asking for confirmation.

Viewing and Editing Files

Viewing File Contents

Display the entire file:

bash

cat myfile.txt

View a file one page at a time:

bash

less myfile.txt

(Press q to exit less)

See the first 10 lines of a file:

bash

head myfile.txt

See the last 10 lines of a file:

bash

tail myfile.txt

Follow a file in real-time (useful for logs):

bash

tail -f /var/log/syslog

Basic Text Editors

Debian comes with several text editors:

1. nano - Beginner-friendly:

bash

nano myfile.txt

Common nano shortcuts:

• Ctrl+O: Save file
• Ctrl+X: Exit
• Ctrl+G: Help

2. vim - More advanced:

bash

vim myfile.txt

Basic vim commands:

• i: Enter insert mode
• Esc: Return to command mode
• :w: Save file
• :q: Quit
• :wq: Save and quit

Command Execution and Control

Running Commands

Execute a command:

bash

echo "Hello, Debian!"

Output:

Hello, Debian!

Run multiple commands on one line:

bash

mkdir test && cd test && touch newfile.txt

Command History

View command history:

bash

history

Re-run the previous command:

bash

!!

Search through command history:

• Press Ctrl+R and start typing
• Press Ctrl+R again to cycle through matches

Keyboard Shortcuts

Useful terminal shortcuts:

• Ctrl+C: Terminate the current command
• Ctrl+Z: Suspend the current command
• Ctrl+D: Log out of current session
• Ctrl+L: Clear the screen (same as clear command)
• Tab: Auto-complete commands and filenames

Input/Output and Redirection

Standard Streams

Bash uses three main streams:

• Standard input (stdin): Input to commands
• Standard output (stdout): Normal command output
• Standard error (stderr): Error messages

Redirection Operators

Redirect output to a file (overwrites):

bash

echo "This is a test" > output.txt

Append output to a file:

bash

echo "More text" >> output.txt

Redirect errors to a file:

bash

command 2> errors.txt

Redirect both output and errors to different files:

bash

command > output.txt 2> errors.txt

Redirect both output and errors to the same file:

bash

command > all.txt 2>&1
# Or using newer syntax
command &> all.txt

Pipes

Pipes connect the output of one command to the input of another:

bash

ls -l | grep "\.txt"

Chain multiple commands:

bash

cat /var/log/syslog | grep ERROR | less

Finding Things

Locate Files

Search for files by name:

bash

find /home -name "*.txt"

Find files modified within the last 24 hours:

bash

find /home -mtime -1

Find files larger than 10MB:

bash

find /home -size +10M

Search File Contents

Search for text in files:

bash

grep "search_term" file.txt

Recursive search in a directory:

bash

grep -r "search_term" /home/username/Documents

Case-insensitive search:

bash

grep -i "search_term" file.txt

Bash Variables and Environment

Working with Variables

Assign a value to a variable:

bash

my_var="Hello World"

Access a variable's value:

bash

echo $my_var

Output:

Hello World

Environment Variables

Display all environment variables:

bash

env

Display a specific environment variable:

bash

echo $HOME

Set an environment variable for the current session:

bash

export MY_VAR="some value"

The PATH Variable

The PATH variable tells Bash where to look for executable files:

bash

echo $PATH

Output might look like:

/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

Add a directory to your PATH temporarily:

bash

export PATH=$PATH:/new/directory

Introduction to Bash Scripting

Your First Bash Script

1. Create a file named hello.sh:

bash

touch hello.sh

2. Edit the file with nano:

bash

nano hello.sh

3. Add the following content:

bash

#!/bin/bash

# This is a comment
echo "Hello, Debian Bash Scripting!"
echo "Current date and time: $(date)"
echo "Your username is: $USER"

4. Save and exit (Ctrl+O, Enter, Ctrl+X in nano)

5. Make the script executable:

bash

chmod +x hello.sh

6. Run the script:

bash

./hello.sh

Output:

Hello, Debian Bash Scripting!
Current date and time: Thu Mar 13 15:45:32 EDT 2025
Your username is: username

Basic Script Structure

A typical bash script includes:

bash

#!/bin/bash

# Script description
# Author: Your Name
# Date: March 13, 2025

# Variables
greeting="Hello"
name="World"

# Main code
echo "$greeting, $name!"

# Exit with success status
exit 0

Conditional Statements

Basic if-else structure:

bash

#!/bin/bash

file="test.txt"

if [ -f "$file" ]; then
    echo "The file $file exists."
else
    echo "The file $file does not exist."
    touch "$file"
    echo "The file $file has been created."
fi

Loops

For loop example:

bash

#!/bin/bash

echo "Counting from 1 to 5:"

for i in {1..5}; do
    echo "Number: $i"
done

While loop example:

bash

#!/bin/bash

counter=1

while [ $counter -le 5 ]; do
    echo "Counter: $counter"
    ((counter++))
done

Practical Examples

Example 1: System Information Script

Create a script that displays basic system information:

bash

#!/bin/bash

echo "===== System Information ====="
echo "Hostname: $(hostname)"
echo "Kernel Version: $(uname -r)"
echo "CPU Information: $(lscpu | grep 'Model name' | sed 's/Model name: *//')"
echo "Memory Information:"
free -h
echo "Disk Usage:"
df -h | grep '^/dev/'
echo "============================="

Example 2: Backup Script

A simple script to create a backup of important files:

bash

#!/bin/bash

# Configuration
backup_dir="/home/username/backups"
source_dir="/home/username/Documents"
date_format=$(date +%Y-%m-%d-%H-%M-%S)
backup_file="backup-$date_format.tar.gz"

# Create backup directory if it doesn't exist
mkdir -p "$backup_dir"

# Create the backup
echo "Creating backup of $source_dir..."
tar -czf "$backup_dir/$backup_file" "$source_dir"

# Check if backup was successful
if [ $? -eq 0 ]; then
    echo "Backup created successfully: $backup_dir/$backup_file"
    echo "Backup size: $(du -h "$backup_dir/$backup_file" | cut -f1)"
else
    echo "Backup failed!"
    exit 1
fi

# List existing backups
echo "Existing backups:"
ls -lh "$backup_dir" | grep "backup-"

exit 0

Example 3: Log File Analyzer

Script to analyze a log file for errors:

bash

#!/bin/bash

# Configuration
log_file="/var/log/syslog"
search_term="error"

# Check if log file exists
if [ ! -f "$log_file" ]; then
    echo "Error: Log file $log_file does not exist."
    exit 1
fi

# Count occurrences of the search term
echo "Analyzing $log_file for '$search_term'..."
count=$(grep -i "$search_term" "$log_file" | wc -l)
echo "Found $count occurrences of '$search_term'"

# Display the most recent errors
echo "Most recent errors:"
grep -i "$search_term" "$log_file" | tail -5

exit 0

Command Flow Visualization

Here's a visualization of how commands flow in the Bash shell:

Summary

In this tutorial, we've covered the essential Bash basics for Debian Linux:

• Terminal navigation and file operations
• Viewing and editing files
• Command execution and control
• Input/output redirection and pipes
• Finding files and searching content
• Working with variables and environment
• Introduction to Bash scripting with practical examples

Mastering these fundamentals will provide you with a solid foundation for efficiently working with Debian systems and developing more advanced shell scripts.

Additional Resources and Exercises

Resources for Further Learning

1. The Bash manual: Access through man bash
2. GNU Bash documentation: GNU Bash Manual
3. Debian Documentation: Debian Manuals

Practice Exercises

1. Navigation Challenge:

   • Create a directory structure with at least 3 levels
   • Navigate between directories using both absolute and relative paths
   • Create files at different levels and list them

2. File Manipulation:

   • Create a file with some text
   • Copy it to a new location
   • Append more text to it
   • Count the number of words and lines in the file

3. Simple Script Creation:

   • Write a script that asks for the user's name and greets them
   • Make the script executable and run it

4. Advanced Script Project:

   • Create a script that monitors system resources (CPU, memory, disk) and logs the information
   • Add a feature to alert when resources exceed certain thresholds

5. Redirection Practice:

   • Use redirection to combine the contents of multiple files
   • Use pipes to filter and transform text data

Remember, the best way to learn Bash is by practicing regularly. Start with simple commands and scripts, then gradually tackle more complex tasks as you build confidence and understanding.