Overview of Common Linux Shell Commands

1. What is a Shell?

Definition

A shell is a powerful command-line interpreter used in Unix-like operating systems (like Linux and macOS).

• It acts as both:
  • An interactive command language for users to interact with the OS.
  • A scripting language for automating tasks.

Common Shells in Linux

In this course, we will use Bash, the default shell on most Linux systems.

How to Check Your Current Shell

printenv SHELL

Example output:

/bin/bash

If not Bash, you can switch by typing:

bash

2. Applications of Shell Commands

Shell commands are essential for various tasks such as:

3. Common Shell Commands

A. System Information Commands

B. File Management Commands

C. Directory Navigation Commands

D. File Content Viewing Commands

E. File Compression & Archiving

F. Networking Commands

4. Running Linux on Windows

You can run Linux commands on a Windows machine using these methods:

5. Summary

✅ The role of a shell in Linux as both a command interpreter and scripting tool.
✅ How to check and switch shells using commands like printenv SHELL and bash.
✅ The main applications of shell commands across system info, file management, networking, and automation.
✅ The most common shell commands grouped by function for easy reference.

Quick Reference Table

🔧 Linux Shell Commands Cheat Sheet

This cheat sheet includes common Linux shell commands, their syntax, and examples. Designed for quick reference and learning.

🧑‍💻 Basic Navigation

🗂️ File & Directory Management

📄 Viewing and Editing Files

🔍 Searching and Filtering

🧰 System Information

📦 Compression & Archiving

🌐 Networking

💾 Package Management

Debian/Ubuntu (.deb)

Red Hat/CentOS/Fedora (.rpm)

🖥️ Shell Utilities

Linux Informational Commands Cheat Sheet

🔍 1. User & Identity Info

🖥️ 2. Operating System Info

💾 3. Disk Usage Info

-h makes output human-readable (e.g., GB instead of bytes)

🔄 4. Process Monitoring

🖨️ 5. Printing Strings, Variables, and Dates

📚 6. Command Manuals

📚 Getting Help for Linux Commands – A Complete Guide

When working with Linux, knowing how to find help is just as important as knowing the commands themselves. Here’s a structured approach to getting assistance when you’re stuck or curious.

🔍 1. Use the Built-in man Command

The man (manual) command is the traditional and most comprehensive way to get help in Linux.

🧾 How to Use It:

man command_name

Example:

man ls

📘 Man Page Sections:

📋 View All Available Man Pages:

man -k .

This lists all commands with manual pages and a short description.

📝 2. Install and Use the tldr Command

tldr provides simplified, example-based help for common commands — perfect for quick reference.

💾 Install it:

If Node.js is installed:

npm install -g tldr

🚀 Usage:

tldr ls

You’ll see concise examples like:

ls
List directory contents.

- List files one per line:
  ls -1

- List all files, including hidden ones:
  ls -a

Ideal for users who want just enough info to get the job done.

💬 3. Search Stack Overflow

Stack Overflow is a powerful community-driven Q&A platform for developers and sysadmins.

🔍 Tips for Searching:

• Use the search bar on https://stackoverflow.com/questions/tagged/linux
• Include relevant tags: linux, bash, shell, command-line
• Check the date of answers and read comments for context

📌 Example query:
"how to delete a file in linux" site:stackoverflow.com

🤖 4. Search Stack Exchange (Unix & Linux)

Unix & Linux Stack Exchange is ideal for deeper technical questions.

🎯 Best For:

• More detailed explanations than Stack Overflow
• Complex issues involving system administration, scripting, or obscure commands

🔍 5. Just Google It!

Sometimes, a simple web search is the fastest way to solve a problem.

✅ Tips:

• Include keywords like Linux, Ubuntu, or bash
• Add sources like site:wikipedia.org or site:askubuntu.com
• Avoid blindly trusting old or unverified results

📋 6. Use Course Cheat Sheets

Throughout this course, you’ll encounter cheat sheets that:

• Condense key commands into easy-to-reference formats
• Help you review and apply concepts faster
• Are great for exam prep and real-world use

📄 7. Refer to Wikipedia’s List of Unix Commands

Wikipedia maintains a list of Unix/Linux commands: 🔗 List of Unix Commands (Wikipedia)

Includes:

• Command name
• Category (e.g., Filesystem, Process management)
• Description
• First appearance (e.g., Version 7 AT&T UNIX)

Great for historical context and discovering lesser-known utilities.

🧠 Summary Table: Ways to Get Help

📌 Exercise 1 - Informational Commands

In this exercise, you explored several Linux commands that provide valuable system and user information. These commands are essential for understanding your environment, troubleshooting issues, and monitoring system performance.

🔍 Overview of Commands Covered

🧾 Detailed Breakdown

✅ 1.1 Display Current User

whoami

• Output: theia
• Tells you which user is currently logged in.

✅ 1.2 Get OS Info with uname

uname

• Outputs: Linux

To get full system info:

uname -a

This includes:

• Kernel name
• Hostname
• Kernel release
• Kernel version
• Machine hardware name
• Processor type
• Operating system

✅ 1.3 View User Identity

id

• Shows:
  • uid: User ID
  • gid: Group ID
  • List of groups the user belongs to

✅ 1.4 Check Disk Space

df

• Shows disk usage in 512-byte blocks

For human-readable format:

df -h

• Shows sizes in KB, MB, GB

✅ 1.5 View Running Processes

ps

• Lists processes owned by the current user

To see all processes:

ps -e

✅ 1.6 Real-Time Process Monitoring with top

top

• Gives live updates of:
  • Running processes
  • CPU and memory usage
  • System uptime
  • Load average

To exit: Press q or Ctrl + C
To limit refreshes:

top -n 10

Sorting options (while top is running):

• Shift + M → Sort by memory
• Shift + P → Sort by CPU usage
• Shift + N → Sort by PID
• Shift + T → Sort by runtime

✅ 1.7 Print Messages with echo

echo "Welcome to the Linux lab"

Output:

Welcome to the Linux lab

Use -e to interpret escape characters:

echo -e "Line one\nLine two"

Output:

Line one
Line two

Common escape characters:

• \n – New line
• \t – Tab

✅ 1.8 Show Date and Time

date

• Shows full current date and time

Custom formats:

date "+%D"     # mm/dd/yy
date "+%Y-%m-%d %T"  # 2025-04-05 14:30:00

Popular format specifiers:

✅ 1.9 View Manual Pages

man ls

• Opens the manual page for the ls command

To list all available man pages:

man -k .

Man pages typically include:

• NAME
• SYNOPSIS
• DESCRIPTION
• OPTIONS
• EXAMPLES
• SEE ALSO

📋 Summary Table

💡 Tips & Best Practices

• Use --help with many commands for quick usage examples:

  ls --help

• Combine man and tldr for both depth and speed:

  tldr df

• Use watch for repeated execution:

  watch df -h

📚 Practice Exercises with Solutions

Here are the practice exercises along with hints and complete solutions to reinforce your understanding of essential Linux commands.

🔹 1. Get basic information about the operating system

💡 Hint:

Use the uname command for kernel and OS-related information.

✅ Solution:

uname -a

This will display detailed system information, including:

• Kernel name
• Hostname
• Kernel release version
• Machine hardware name
• Operating system

🔹 2. View all running processes on the system

💡 Hint:

The ps command lists running processes. Use an option to show all processes.

✅ Solution:

ps -e

This shows every process currently running on the system, not just those owned by the current user.

🔹 3. Get the table of processes and sort by memory usage

💡 Hint:

Use the top command and a keyboard shortcut to sort by memory.

✅ Solution:

top

Once inside top, press:

Shift + M

This sorts the list by memory usage, allowing you to quickly identify which processes are using the most RAM.

To exit top, press q.

🔹 4. Display the current time

💡 Hint:

Use the date command with a format specifier to show only the time.

✅ Solution:

date "+%T"

Output example:

14:25:36

Other useful formats:

• date "+%H:%M" → 14:25
• date "+%r" → 02:25:36 PM

🔹 5. Using one command, display the messages “Hello!” and “Goodbye!” separated by a new line

💡 Hint:

Use the echo command with the -e option to interpret escape sequences like \n.

✅ Solution:

echo -e "Hello!\nGoodbye!"

Output:

Hello!
Goodbye!

The -e flag enables interpretation of backslash escapes like \n (new line) and \t (tab).

🎯 Bonus Tips

• Combine echo with redirection to write text into files:

  echo "Hello World" > hello.txt

• Use watch to monitor changing output:

  watch "ps -e | head -n 10"

File and Directory Navigation Commands in Linux

Introduction

This video introduces the essential Linux commands for navigating files and directories. After watching, you will be able to:

✅ Use ls to list directory contents
✅ Navigate between directories using cd
✅ Understand relative vs absolute paths
✅ Search for files using the find command

1. List Files and Directories: ls Command

Purpose

The ls (list) command is used to display the contents of a directory.

Basic Usage

• To list files in the current directory:

  ls

• To list files in a specific directory:

  ls Downloads

Common Options

The output from ls -l includes:

• File type and permissions (drwxr-xr-x)
• Number of links
• Owner name
• Group name
• Size in bytes
• Date of last modification
• File or directory name

2. Show Current Working Directory: pwd

Purpose

The pwd (print working directory) command shows your current location in the file system.

Usage

pwd

Example Output:

/home/user/Documents

Useful when:

• You’re unsure which directory you are in.
• You want to verify your location before running commands.

3. Change Directory: cd Command

Purpose

The cd (change directory) command lets you move between directories.

Basic Syntax

cd <directory_path>

Examples

Understanding Path Types

4. Find Files: find Command

Purpose

The find command helps you locate files and directories based on various criteria like name, type, size, etc.

Basic Syntax

find <starting_directory> <options>

Common Examples

Tip: The . means “start searching here” — it’s useful when you want to limit the scope of your search.

5. Summary of Key Concepts

✅ ls – Listing Contents

• Lists files and directories.
• Use options like -l, -a, and -la for more detailed views.

✅ pwd – Knowing Where You Are

• Displays the full path of the current working directory.

✅ cd – Moving Around

• Supports both absolute and relative paths.
• Use ~ to go to your home directory.
• Use .. to move up one level.

✅ find – Searching Efficiently

• Powerful tool for locating files and folders.
• Can use exact names, wildcards, case-insensitive searches, and filters by type.

6. Quick Reference Table

7. Final Thoughts

Mastering these navigation commands gives you control over your Linux environment. Whether you’re organizing files, troubleshooting issues, or writing scripts, understanding how to navigate the filesystem efficiently is crucial.

File and Directory Management Commands in Linux V2

1. Introduction

✅ Creating and deleting files and directories
✅ Copying and moving files and folders
✅ Managing file permissions (e.g., making a script executable)

These commands are essential for managing your system, organizing data, and working with scripts or configuration files.

2. Creating and Removing Files and Directories

A. mkdir – Make Directory

• Purpose: Create new directories.
• Syntax:

  mkdir <directory_name>

• Example:

  mkdir test

Creates a directory named test in the current location.

B. rm – Remove Files or Directories

• Purpose: Delete files or directories.

• Syntax:

  rm <filename>

• Remove a file:

  rm file1.txt

• Remove a directory and its contents:

  rm -r folder1

⚠️ Warning: Use rm -r carefully — it deletes everything inside the directory recursively.

C. rmdir – Remove Empty Directories

• Purpose: Delete only empty directories.

• Syntax:

  rmdir <directory_name>

• Example:

  rmdir empty_folder

If the folder contains files or subdirectories, this command will fail — use rm -r instead.

D. touch – Create Empty Files or Update Timestamps

• Purpose: Create an empty file or update the last-modified timestamp of an existing one.

• Syntax:

  touch <filename>

• Create multiple files:

  touch a.txt b.txt c.txt

• Update timestamp on an existing file:

  touch notes.txt

Useful for testing, scripting, or resetting file timestamps.

3. Copying and Moving Files and Directories

A. cp – Copy Files or Directories

• Purpose: Copy files from one location to another.

• Syntax:

  cp <source> <destination>

• Copy a single file:

  cp notes.txt Documents/

• Copy and rename a file:

  cp notes.txt Documents/backup_notes.txt

• Copy a directory and all contents:

  cp -r Documents Docs_copy

The -r option enables recursive copying of directories and their contents.

B. mv – Move or Rename Files/Directories

• Purpose: Move files/dirs or rename them.

• Syntax:

  mv <source> <destination>

• Move a file into a directory:

  mv my_script.sh Scripts/

• Rename a file:

  mv old_name.txt new_name.txt

• Move multiple directories into another:

  mv Scripts Notes Documents/

Unlike cp, mv does not duplicate the original — it moves or renames.

4. Managing File Permissions with chmod

A. chmod – Change File Mode (Permissions)

• Purpose: Set or change read, write, and execute permissions on files.
• Syntax:

  chmod [options] <filename>

Common Options

Example: Making a Script Executable

chmod +x my_script.sh

• Before:

  -rw-r--r-- 1 user group 0 Jan 1 12:00 my_script.sh

• After:

  -rwxr-xr-x 1 user group 0 Jan 1 12:00 my_script.sh

Now you can run the script:

./my_script.sh

5. Summary of Key Commands

6. Final Tips

• Always double-check before using rm -r — it’s irreversible.
• Use rmdir when removing empty directories to avoid accidental deletion.
• chmod is essential for running scripts or setting up secure environments.
• Combine these commands with others like ls, cd, and find for powerful file operations.

📁 Exercise 1 - Navigating Files and Directories

In this exercise, you practiced essential Linux commands for navigating the filesystem, listing directory contents, and understanding file patterns.

📍 1.1 Get the Location of the Present Working Directory

Command:

pwd

What It Does:

• Stands for “Print Working Directory”
• Shows the full path to the directory where you are currently located

Example output:

/home/theia

📋 1.2 List Files and Directories in a Directory

Basic Usage:

ls

• Lists all non-hidden files and directories in the current location
• If the directory is empty, it returns nothing

View Contents of /bin (Binary Directory):

ls /bin

• Displays system-level commands like ls, cd, cp, etc.
• You can also look at specific files:

  ls /bin/ls

Use Wildcards to Match Patterns:

🔍 All files starting with b:

ls /bin/b*

🔍 All files ending with r:

ls /bin/*r

💡 The * wildcard matches any number of characters

📄 Long Listing Format

See detailed file information:

ls -l

Includes:

• File type and permissions
• Number of links
• Owner
• Group
• Size in bytes
• Last modification date/time
• File or directory name

Common ls Options:

Example: List all files (including hidden ones) in long format:

ls -la

Example: List all files in /etc with details:

ls -la /etc

This helps you explore system-wide configuration files.

✅ Summary Table

💡 Pro Tips

• Combine options:

  ls -lah   # Long list, human-readable, include hidden

• Use tab completion to avoid typing full paths:

  ls /bi<TAB>

  Becomes:

  ls /bin/

📁 Exercise 2 - Creating Files and Directories

In this exercise, you practiced using Linux commands to create directories, navigate the filesystem, and create or update files using the touch command.

✅ Summary of Commands Covered

🧾 Step-by-Step Breakdown

🔹 2.1 Create a Directory with mkdir

mkdir scripts

• Creates a new directory named scripts in your current location

Verify it was created:

ls

You should see scripts listed.

🔹 2.2 Change Working Directory with cd

Move into the scripts directory:

cd scripts

Check your current location:

pwd

Return to your home directory:

cd

Move up one level (to the parent directory):

cd ..

This is useful when navigating through nested directories.

🔹 2.3 Create an Empty File with touch

Go back to your home directory:

cd

Create a new file called myfile.txt:

touch myfile.txt

Verify the file exists:

ls

If the file already exists, touch updates its last-modified timestamp:

touch myfile.txt

To check the updated timestamp:

date -r myfile.txt

This shows the last time the file was accessed or modified.

📋 Tips & Tricks

• You can create multiple directories at once:

  mkdir dir1 dir2 dir3

• Make a nested directory structure easily:

  mkdir -p project/files/data

  The -p option creates parent directories as needed.
• Use tab completion for faster navigation:

  cd scri<TAB>

  Completes to:

  cd scripts

🧠 Why These Commands Matter

These basic tools are essential for managing your workspace in Linux:

• mkdir: Organize your files by creating structured directories
• cd: Navigate between folders quickly
• touch: Create placeholder files or update timestamps for testing or scripting purposes

📁 Exercise 3 - Managing Files and Directories

In this exercise, you practiced essential Linux commands for searching, removing, moving, renaming, and copying files and directories — key skills for managing your system effectively.

✅ Summary of Commands Covered

🔍 Step-by-Step Breakdown

🔹 3.1 Search for Files Using find

find /etc -name '*.txt'

• Searches the /etc directory and its subdirectories for all .txt files.
• -name specifies a filename pattern to match.
• You may see “Permission denied” errors — these are normal due to access restrictions in lab environments.

🔹 3.2 Remove Files with rm

rm -i myfile.txt

• The -i option prompts for confirmation before deletion:

  rm: remove regular file 'myfile.txt'? y/n

After deletion, verify:

ls

⚠️ Warning: Deleted files cannot be recovered easily. Always double-check what you’re deleting.

Use without -i only when sure:

rm myfile.txt

Delete multiple files safely using confirmation:

rm -i *.txt

🔹 3.3 Move or Rename Files with mv

✏️ Rename a File:

mv users.txt user-info.txt

This renames users.txt to user-info.txt in the same directory.

Verify:

ls

📦 Move a File to Another Directory:

mv user-info.txt /tmp

Moves user-info.txt to the /tmp directory.

Verify:

ls
ls -l /tmp

💡 If the target file already exists, it will be overwritten silently — always be cautious!

🔹 3.4 Copy Files with cp

📄 Copy from One Location to Another:

cp /tmp/user-info.txt user-info.txt

This copies the file back to your current working directory.

Verify:

ls

📂 Copy Content of a System File:

cp /etc/passwd users.txt

This creates a new file users.txt containing the contents of /etc/passwd.

Check that the copy was successful:

ls
cat users.txt

You can also view the first few lines:

head users.txt

🧰 Pro Tips

• Use wildcards to move or copy groups of files:

  cp *.txt /backup/
  mv *.log logs/

• Combine cp with -r to copy entire directories:

  cp -r myfolder/ backup/

• Use rm -r carefully to delete directories and their contents:

  rm -r myfolder

🧠 Why These Commands Matter

These tools give you full control over your filesystem:

• find: Locate files across your system
• rm: Clean up unwanted files
• mv: Reorganize or rename files
• cp: Duplicate or archive content

They form the foundation for automating tasks, writing scripts, and managing data efficiently.

📚 Practice Exercises – Managing Files and Directories

Here are the practice exercises with hints and solutions to help reinforce your understanding of Linux commands for navigating, creating, moving, copying, and deleting files and directories.

🔹 1. Display the contents of the /home directory

💡 Hint:

Use the ls command to list directory contents.

✅ Solution:

ls /home

This shows all user directories inside /home.

🔹 2. Ensure that you are in your home directory

💡 Hint:

Use the cd command without arguments to return to your home directory.

✅ Solution:

cd

You can verify using:

pwd

It should output something like:

/home/theia

🔹 3. Create a new directory called tmp and verify its creation

💡 Hint:

Use mkdir to create a directory and ls to confirm it exists.

✅ Solution:

mkdir tmp
ls

You should see tmp listed in the output.

🔹 4. Create a new, empty file named display.sh in the tmp directory, and verify its creation

💡 Hint:

Navigate into the tmp directory and use touch to create an empty file.

✅ Solution:

cd tmp
touch display.sh
ls

You should see display.sh listed.

🔹 5. Create a copy of display.sh, called report.sh, within the same directory

💡 Hint:

Use the cp command to make a copy of a file.

✅ Solution:

cp display.sh report.sh
ls

Now both display.sh and report.sh should be listed.

🔹 6. Move your copied file, report.sh, up one level in the directory tree to the parent directory. Verify your changes

💡 Hint:

Use mv to move the file and cd .. or ls -l ../ to check.

✅ Solution:

mv report.sh ..
ls ..

Or:

cd ..
ls

You should now see report.sh in the parent directory.

🔹 7. Delete the file display.sh

💡 Hint:

Use the rm command to delete a file. Consider using -i for confirmation (optional).

✅ Solution:

rm display.sh

To verify:

ls

The file display.sh should no longer appear.

🔹 8. List the files in /etc directory in the ascending order of their access time

💡 Hint:

Use the ls command with appropriate options to sort by access time.

✅ Solution:

ls -ltu /etc

• -l = long listing format
• -t = sort by modification time (but combined with -u, sorts by access time)
• -u = use access time for sorting

This lists files sorted by when they were last accessed, newest first.

🔹 9. Copy the file /var/log/bootstrap.log to your current directory

💡 Hint:

Use the cp command to copy a file from its source path to the current directory.

✅ Solution:

cp /var/log/bootstrap.log .

To verify:

ls

You should see bootstrap.log in your current directory.

🧠 Bonus Tips

• Use tab completion to avoid typing full paths:

  cp /va<TAB>/lo<TAB>/boo<TAB> .

• Combine ls options for better readability:

  ls -lh

• Use rm -i when unsure:

  rm -i *.tmp

Great job completing these hands-on exercises! You’re now comfortable with basic file and directory management in Linux.

🔒 Security: Managing File Permissions and Ownership – Summary & Guide

In this reading, you learned how to manage file permissions and ownership in Linux — a crucial skill for protecting sensitive data and ensuring system security.

🎯 Learning Objectives Recap

By the end of this section, you should be able to:

• Explain file ownership and permissions
• View file and directory permissions
• Make files private by changing permission settings

🔐 Why File Permissions Matter

Linux is a multi-user operating system, which means multiple people can access the same machine. Without proper permissions:

• Anyone could read or modify your files
• Malicious users might execute harmful scripts
• Sensitive documents (like tax records or company IP) could be exposed

That’s why permissions and ownership allow fine-grained control over who can read, write, or execute files.

👤 Types of Owners in Linux

There are three categories of users that determine permission levels:

Each category has its own set of permissions:

• r = Read
• w = Write
• x = Execute

👀 Viewing File Permissions

Use:

ls -l filename

Example output:

-rw-r--r-- 1 theia users 25 Dec 22 17:47 my_new_file

• -: Indicates it’s a regular file
• rw-: User (owner) permissions
• r--: Group permissions
• r--: Others’ permissions

📘 For directories:

• d at the start indicates it’s a directory
• Permissions mean:
  • r: Can list contents (ls)
  • w: Can create or delete files inside
  • x: Can enter the directory (cd)

🔧 Changing File Permissions with chmod

You can change permissions using:

chmod [options] filename

Example: Make a file private

chmod go-r my_new_file

This removes read permission for group and others.

After running:

ls -l my_new_file

You’ll see:

-rw------- 1 theia users 24 Dec 22 18:49 my_new_file

Now only the owner can read and write to the file.

⚠️ Only the owner or root can change permissions on a file.

🛠️ Common chmod Syntax Options

Numeric Permission Notation

Each permission level has a number value:

• r = 4
• w = 2
• x = 1

Sum them to get numeric values:

Example:

chmod 600 secret.txt

Only the owner has read and write access.

📁 Executable Files and Shell Scripts

To make a shell script executable:

1. Add a shebang line at the top:

   #!/bin/bash

2. Give it execute permission:

   chmod +x script.sh

3. Run it:

   ./script.sh

This tells the OS that the file is a program written in Bash (or another interpreter).

✅ Summary Table

💡 Pro Tips

• Use chmod 700 folder to keep a directory private
• Protect sensitive scripts with chmod 600 script.sh
• Use id to see what groups you belong to
• Use chown (as root) to change file ownership

You’re now equipped with the knowledge to secure your files, control access, and protect sensitive data in a Linux environment.

🛠️ Exercise 1 - Viewing and Modifying File Access Permissions

In this exercise, you learned how to view and modify file permissions in Linux using the ls -l and chmod commands. Understanding and managing permissions is essential for maintaining system security and controlling access to your files.

📁 1.1 View File Access Permissions

🔧 Steps:

1. Navigate to your project directory:

   cd /home/project

2. Download the required file:

   wget https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBM-LX0117EN-SkillsNetwork/labs/module%201/usdoi.txt

3. View the file’s permissions:

   ls -l usdoi.txt

✅ Sample Output:

-rw-r--r-- 1 theia theia 8121 May 31 16:45 usdoi.txt

📝 Breakdown of Permission String: -rw-r--r--

🔐 1.2 Change File Access Permissions with chmod

The chmod command allows you to modify who can read, write, or execute a file.

🔧 Syntax:

chmod [who][operator][permission] filename

🔍 Example Commands

❌ Remove read permission for all users:

chmod -r usdoi.txt

Verify:

ls -l usdoi.txt

You’ll see something like:

--w------- 1 theia theia 8121 May 31 16:45 usdoi.txt

✅ Restore read permission for all users:

chmod +r usdoi.txt

Verify:

ls -l usdoi.txt

You should return to:

-rw-r--r-- 1 theia theia 8121 May 31 16:45 usdoi.txt

🚫 Remove read permission only for “other”:

chmod o-r usdoi.txt

Verify:

ls -l usdoi.txt

Now output will be:

-rw-r----- 1 theia theia 8121 May 31 16:45 usdoi.txt

Only user and group can read the file now.

🧠 Summary Table

💡 Pro Tips

• Use numeric mode for precision:

  chmod 644 usdoi.txt    # rw-r--r--
  chmod 700 secret.sh     # rwx------

• Always double-check permissions on sensitive files:

  ls -l secret.txt

• Only the file owner or root can change permissions.

Great job completing this exercise! You’re now able to view and manage file permissions — an essential skill for working securely in Linux.

📁 Exercise 2 - Understanding Directory Access Permissions

In this exercise, you explored how directory permissions in Linux work and how they differ from file permissions. You learned that execute (x) permission is required to enter a directory, and write (w) permission is needed to create or delete files inside it.

🔍 Summary of What You Learned

⚠️ Even if you have write access, you can’t modify contents without execute permission!

🧾 Step-by-Step Breakdown

🔹 2.1 View Default Directory Access Permissions

Create a new directory:

cd /home/project
mkdir test

Check its permissions:

ls -l

Output example:

drwxr-sr-x 2 theia users 4096 May 15 14:06 test

• d: Indicates it’s a directory
• rwx: Owner (user) has read, write, and execute
• r-s: Group has read and setgid (special permission)
• r-x: Others have read and execute

You verified that:

• You could enter the directory
• You could create a subdirectory inside it

Commands used:

cd test
mkdir test2
cd ..

💡 The s in group permissions is a special flag called setgid — it ensures new files inherit the group of the parent directory.

🔹 2.2 Remove User Execute Permissions

Remove execute permission for owner:

chmod u-x test

Now try:

cd test

❌ Output:

bash: cd: test: Permission denied

Even though you still have read and write permissions, you can’t enter the directory without execute permission.

Try listing contents:

ls -l test

✅ Works — because you still have read permission.

Try creating a subdirectory:

mkdir test/test3

❌ Fails — because write requires execute.

🔁 Restore Permissions

Add back execute:

chmod u+x test

Remove write:

chmod u-w test

Check current permissions:

ls -l

Now try:

cd test
mkdir test_again

❌ Output:

mkdir: cannot create directory ‘test_again’: Permission denied

You can enter the directory (thanks to x), but you can’t modify it (because you don’t have w).

🧠 Key Takeaways

🧩 Think of x as a key to open a door — you need it before you can do anything useful inside a directory.

✅ Summary Table

You’ve now mastered how directory permissions control access differently than file permissions — an essential concept for securing and managing your Linux system effectively.

🛠️ Practice Exercises – File and Directory Permissions

Here are the practice exercises with hints and full solutions to help you reinforce your understanding of Linux file and directory permissions.

🔹 1. List the permissions set for the file usdoi.txt

💡 Hint:

Use the ls -l command to view file permissions.

✅ Solution:

ls -l usdoi.txt

Example output:

-rw-r--r-- 1 theia users 8121 May 31 16:45 usdoi.txt

This shows that:

• The owner has read and write
• The group has read
• Others have read

🔹 2. Revoke the write permission on usdoi.txt for the user, and verify

💡 Hint:

Use chmod u-w to remove write access for the user.

✅ Solution:

chmod u-w usdoi.txt
ls -l usdoi.txt

New output:

-r--r--r-- 1 theia users 8121 May 31 16:45 usdoi.txt

The user (owner) no longer has write permission.

🔹 3. What happens if you try to delete usdoi.txt after revoking write permissions?

💡 Hint:

You don’t need write permission to delete a file — but you do need write permission in the directory it’s in.

✅ Solution:

Try deleting:

rm usdoi.txt

✅ It works!
Even though you removed write permission on the file, you can still delete it because:

• You own the file
• You have write permission in the directory

🔍 Note: If you didn’t own the file, you could still delete it as long as:

• You had write permission in the directory
• You didn’t own the file

🔹 4. Create a new directory called tmp_dir in your home directory

💡 Hint:

Use the mkdir command.

✅ Solution:

cd ~
mkdir tmp_dir

Now you have a new directory in your home folder.

🔹 5. View the permissions of the newly created directory tmp_dir

💡 Hint:

Use ls -l again to see directory permissions.

✅ Solution:

ls -l

Output will include something like:

drwxr-xr-x 2 theia users 4096 Apr 5 10:00 tmp_dir

This means:

• User: read, write, execute
• Group: read, execute
• Others: read, execute

🔹 6. Revoke the user write permission for tmp_dir

💡 Hint:

Use chmod u-w on the directory.

✅ Solution:

chmod u-w tmp_dir
ls -l

New output:

dr-xr-xr-x 2 theia users 4096 Apr 5 10:00 tmp_dir

User now only has execute and read — not write.

🔹 7. Check whether you can create a subdirectory sub_dir inside tmp_dir

💡 Hint:

Use mkdir to attempt creating a subdirectory.

✅ Solution 1:

mkdir tmp_dir/sub_dir

❌ Output:

mkdir: cannot create directory ‘tmp_dir/sub_dir’: Permission denied

✅ Solution 2 Explanation:

Even though you have execute (x) permission on tmp_dir, which allows you to enter the directory, you don’t have write (w) permission — so you can’t modify its contents (like creating or deleting files or directories).

🧠 Summary Table

Great job working through these permission exercises! You’re building strong skills in managing file access control, user permissions, and directory behavior in Linux.

Viewing File Content in Linux

1. Introduction

✅ Displaying full or partial contents of a file
✅ Navigating large files page-by-page
✅ Counting lines, words, and characters

These tools are especially useful when working with log files, scripts, configuration files, and other text-based data.

2. Commands to View File Contents

A. cat – Concatenate and Print Entire File

• Purpose: Print the entire contents of a file to the terminal.

• Syntax:

  cat <filename>

• Example:

  cat numbers.txt

Outputs all lines from the file numbers.txt, from line 0 to 99 in this example.

• Use Cases:
  • Small files that fit on one screen.
  • Combining multiple files into one (e.g., cat file1 file2 > combined.txt)

⚠️ Not ideal for long files — output may scroll off-screen quickly.

B. more – View File One Page at a Time

• Purpose: Scroll through a file page by page.

• Syntax:

  more <filename>

• Example:

  more numbers.txt

• Navigation Keys:

  • Press Spacebar to go to the next page.
  • Press Enter to scroll one line at a time.
  • Press q to quit and return to the command prompt.

Ideal for reading long files without overwhelming the terminal.

C. head – View First Few Lines of a File

• Purpose: Show the beginning portion of a file.

• Syntax:

  head <filename>

• Default Behavior:

  • Displays first 10 lines of the file.

• Example:

  head numbers.txt

  Shows lines 0–9

• Custom Line Count:

  head -n 3 numbers.txt

  Shows first 3 lines: 0, 1, 2

Useful for checking headers, logs, or sample data quickly.

D. tail – View Last Few Lines of a File

• Purpose: Show the end portion of a file.

• Syntax:

  tail <filename>

• Default Behavior:

  • Displays last 10 lines of the file.

• Example:

  tail numbers.txt

  Shows lines 90–99

• Custom Line Count:

  tail -n 3 numbers.txt

  Shows last 3 lines: 97, 98, 99

• Real-world Use:

  • Monitoring log files in real-time using:

    tail -f /var/log/syslog

3. Command to Analyze File Content: wc

A. wc – Word Count

• Purpose: Count lines, words, and bytes (characters) in a file.

• Syntax:

  wc <filename>

• Example:

  wc pets.txt

Output:

7 7 28 pets.txt

• Meaning:
  • 7 lines
  • 7 words
  • 28 characters (including newline characters)

The character count is higher than expected because wc counts newline characters (\n) as well.

B. Options for Specific Counts

These options let you extract specific metrics without extra parsing.

4. Summary Table

5. Final Tips

• Use cat for small files or quick inspection.
• Use more for navigating larger files interactively.
• Use head and tail to inspect the start or end of a file efficiently.
• Use wc to get statistical information about your file’s content.
• Combine these commands with pipes (|) for advanced analysis:

  cat pets.txt | wc -l

Useful Commands for Wrangling Text Files in Linux

1. Introduction

✅ Sorting lines alphabetically
✅ Removing duplicates
✅ Searching for patterns
✅ Extracting parts of lines
✅ Merging lines from multiple files

These tools are essential for working with log files, CSV data, configuration files, and more.

2. Sorting File Content: sort Command

Purpose

Sort the lines of a file alphabetically or numerically.

Basic Syntax

sort <filename>

Examples

• Sort file alphabetically:

  sort pets.txt

  Output:

  cat
  cat
  cat
  cat
  cat
  dog
  dog

• Sort in reverse order:

  sort -r pets.txt

  Output:

  dog
  dog
  cat
  cat
  cat
  cat
  cat

Tip: Use sort -n for numeric sorting if your file contains numbers.

3. Removing Duplicate Lines: uniq Command

Purpose

Filter out consecutive duplicate lines in a file.

Basic Syntax

uniq <filename>

Example

Given this content in pets.txt:

cat
dog
dog
cat

Running:

uniq pets.txt

Output:

cat
dog
cat

Note: uniq only removes duplicates that appear one after another. To remove all duplicates regardless of position, first use sort, then uniq:

sort pets.txt | uniq

4. Searching for Patterns: grep Command

Purpose

Search for lines containing a specific pattern (e.g., word, phrase, regular expression).

Basic Syntax

grep "pattern" <filename>

Examples

• Search for lines containing “ch”:

  grep "ch" people.txt

  Output:

  Dennis Ritchie
  Erwin Schrodinger

• Case-insensitive search:

  grep -i "ch" people.txt

  Output:

  Charles Babbage
  Dennis Ritchie
  Erwin Schrodinger

grep supports regular expressions for advanced searches:

grep "^C" people.txt   # Find names starting with 'C'

5. Extracting Parts of Lines: cut Command

Purpose

Extract specific characters or fields from each line of a file.

Basic Syntax

cut [options] <filename>

A. Character-Based Extraction

• Extract characters 2 through 9:

  cut -c2-9 people.txt

  Example Input:

  Alan Turing
  Charles Babbage

  Output:

  lan Turin
  harles B

B. Field-Based Extraction

Use -d to define a delimiter and -f to select a field.

• Extract last names (second field) from a space-separated file:

  cut -d' ' -f2 people.txt

  Output:

  Turing
  Babbage

You can also extract multiple fields:

cut -d',' -f1,3 csvfile.csv

6. Merging Lines from Multiple Files: paste Command

Purpose

Combine lines from multiple files side by side, similar to columns in a table.

Basic Syntax

paste <file1> <file2> <file3>

Example

You have three files:

• first.txt:

  Alan
  Charles
  Dennis

• last.txt:

  Turing
  Babbage
  Ritchie

• yob.txt:

  1912
  1791
  1941

Run:

paste first.txt last.txt yob.txt

Output:

Alan    Turing    1912
Charles Babbage   1791
Dennis  Ritchie   1941

By default, paste uses tab as the delimiter.

Custom Delimiter

To use a comma instead:

paste -d',' first.txt last.txt yob.txt

Output:

Alan,Turing,1912
Charles,Babbage,1791
Dennis,Ritchie,1941

7. Summary Table

8. Final Tips

• Combine commands using pipes (|) for powerful workflows:

  sort pets.txt | uniq

• Use grep with wildcards or regex for flexible searching.
• cut is great for parsing structured text like CSV or logs.
• paste helps you create reports or combine related datasets.

📄 Exercise 1 - Viewing File Contents with cat, more, and less

In this exercise, you learned how to view and navigate file contents in the terminal using three essential Linux commands:

• cat – for quick viewing and concatenation
• more – for basic scrolling through a file
• less – for advanced navigation (forward and backward)

These tools are especially useful when working with shell scripts, logs, configuration files, and other text-based data.

🔧 Step-by-Step Breakdown

🏁 Start by navigating to your home directory:

cd ~

🔍 Check what files exist:

ls

You should see a file named entrypoint.sh. .sh is the extension used for shell scripts, which are executable text files that contain Bash commands.

✅ 1.1 View File Content with cat

Command:

cat entrypoint.sh

What It Does:

• Displays the entire contents of the file at once
• Stops at the end and returns to the command prompt

⚠️ If the file is longer than your terminal window, you’ll only see the last part — it scrolls past too quickly to read everything.

💡 Use Cases:

• Quick inspection of small files
• Concatenating multiple files:

  cat file1.txt file2.txt > combined.txt

✅ 1.2 View File Content with more

Command:

more entrypoint.sh

What It Does:

• Shows one screen of text at a time
• Press Spacebar to go to the next page
• Type q to quit

🔍 Useful Info:

The first line:

#!/bin/bash

is called a shebang — it tells the system to use /bin/bash to interpret the script.

📌 You’ll learn more about writing shell scripts later in the course.

💡 Use Cases:

• Reading medium-sized files
• Viewing logs or configuration files from the command line

✅ 1.3 Scroll Through File Content with less

Command:

less entrypoint.sh

What It Does:

• Displays one screen of content
• Allows scrolling forward and backward
  • ↑ / ↓ keys: scroll line by line
  • Page Up / Page Down: scroll page by page
• Press q to exit

🆕 Why less Is Better Than more:

• You can move up and down, not just down
• You can search inside the file with /search_term
• It doesn’t automatically quit at the end

📋 Summary Table

🧠 Tips & Tricks

• Combine with pipes to view output:

  ls -l /etc | less

• Search inside less:
  • Type /pattern then press Enter
  • Press n to find next match
• Exit early: always press q to quit

Great job completing this exercise! You now know how to choose the best tool depending on the size and complexity of the file you’re viewing.

📄 Exercise 2 - Viewing Text File Contents

Using head and tail to View File Content

In this exercise, you learned how to inspect specific parts of a text file using two powerful Linux commands:

• head – to view the beginning of a file
• tail – to view the end of a file

These tools are especially useful for:

• Reading large log files
• Monitoring real-time updates (with tail -f)
• Extracting headers or footers from data files

🧾 Step-by-Step Instructions

🔧 Download and Navigate to Your Project Directory:

cd /home/project
wget https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBM-DB0250EN-SkillsNetwork/labs/Bash%20Scripting/usdoi.txt

Verify the file was downloaded:

ls

You should see usdoi.txt listed.

✅ 2.1 Display the First N Lines with head

Show the first 10 lines (default):

head usdoi.txt

This is helpful when viewing large documents like logs or configuration files where the most important info may be at the top.

Show only the first 3 lines:

head -3 usdoi.txt

Example output:

When in the Course of human events, it becomes necessary for one people to dissolve the political bands which have connected them with another...

💡 Use head to quickly preview files without opening the entire contents.

✅ 2.2 Display the Last N Lines with tail

Show the last 10 lines (default):

tail usdoi.txt

Useful for checking the end of logs or files where recent changes are appended.

Show only the last 2 lines:

tail -2 usdoi.txt

Example output:

...and that government of the people, by the people, for the people shall not perish from the earth.

🚀 Pro Tip: Use tail -f to follow a log file in real time:

tail -f /var/log/syslog

📋 Summary Table

🧠 Why These Commands Matter

• Efficiency: Avoid opening huge files just to check the start or end.
• Monitoring: Track live updates in log files using tail -f.
• Automation: Use in scripts to extract key information from files.

Great work! You now know how to quickly inspect large text files, which is essential for system administration, scripting, and data analysis.

📊 Exercise 3 - Getting Basic Text File Stats with wc

In this exercise, you learned how to use the wc (word count) command to get basic statistics about a text file — including the number of lines, words, and characters.

This is especially useful when:

• You’re analyzing large text files
• You need to verify file contents before processing
• You’re writing scripts that depend on file size or structure

🔧 Step-by-Step Breakdown

Start by navigating to your project directory and using wc:

cd /home/project
wc usdoi.txt

Example Output:

     21     268    1654 usdoi.txt

The output shows:

1. Number of lines
2. Number of words
3. Number of characters
4. File name

✅ View Specific Stats

🔢 Count Lines Only:

wc -l usdoi.txt

Useful for checking how many entries are in a list or log file.

📝 Count Words Only:

wc -w usdoi.txt

Great for content analysis or verifying document length.

🔤 Count Characters Only:

wc -c usdoi.txt

Tells you the total byte size of the file — useful for storage and transmission planning.

💡 Note: wc -c counts bytes, not just visible characters — so whitespace and punctuation are included.

📋 Summary Table

🧠 Why wc Is Useful

• Automation: Use in scripts to validate input data size
• Analysis: Get quick stats without opening the file
• Debugging: Check if a file has expected content structure

You’re doing great! With these tools, you can now analyze text files efficiently and extract meaningful insights from their content.

🧹 Exercise 4 - Basic Text Wrangling: Sorting Lines and Dropping Duplicates

In this exercise, you learned how to clean up and organize text data using two powerful Linux utilities:

• sort – to alphabetically or numerically sort lines
• uniq – to remove consecutive duplicate lines

These tools are essential for:

• Data cleaning
• Log file analysis
• Preparing input for scripts
• Removing redundant output

🔧 Step-by-Step Breakdown

✅ 4.1 Sort Lines Alphanumerically with sort

Display the lines of usdoi.txt sorted alphanumerically:

sort usdoi.txt

This command rearranges all the lines in alphabetical order (A–Z), making it easier to scan or analyze content.

Sort in reverse order (Z–A):

sort -r usdoi.txt

💡 This is useful when you want to see the “end” of an alphabetized list first — like viewing the latest entries in a log.

✅ 4.2 Remove Consecutive Duplicate Lines with uniq

First, download a new file:

wget https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBM-LX0117EN-SkillsNetwork/labs/module%201/zoo.txt

View the contents:

cat zoo.txt

You’ll notice some repeated animal names, especially zebra.

Remove consecutive duplicates:

uniq zoo.txt

This removes only lines that appear one after another, so:

zebra
zebra
lion
tiger
zebra

Becomes:

zebra
lion
tiger
zebra

Only the first two zebras are removed as duplicates — the last one stays because it’s not directly after another zebra.

📋 Summary Table

| Command | Description | | ------------------ | -------------------------------------- | -------------------------------------------- | | sort filename | Sort lines alphabetically | | sort -r filename | Sort lines in reverse order | | uniq filename | Remove consecutive duplicate lines | | sort file | uniq | Sort then remove all duplicates (if grouped) |

🧠 Pro Tips

• To remove all duplicate lines regardless of order:

  sort zoo.txt | uniq

• Count how many times each line appears:

  sort zoo.txt | uniq -c

• Show only lines that appear more than once:

  sort zoo.txt | uniq -d

• Show only lines that appear exactly once:

  sort zoo.txt | uniq -u

🛠️ Real-World Use Cases

| Task | Command | | --------------------------------- | ---------------------------- | ------------------------ | -------- | -------- | ----------- | | Clean up a messy list of emails | sort emails.txt | uniq > clean_emails.txt | | Count unique IP addresses in logs | cut -d' ' -f1 access.log | sort | uniq -c | | Find most frequently visited URLs | awk '{print $7}' access.log | sort | uniq -c | sort -nr | head -n 10 |

Great job mastering these basic but powerful text processing tools! You’re now equipped to organize, clean, and analyze textual data efficiently in Linux.

🧩 Exercise 5 - Basic Text Wrangling: Extracting Lines and Fields

In this exercise, you learned how to filter lines using patterns with grep and extract specific parts of text using the cut command.

These tools are essential for:

• Searching through logs
• Filtering data
• Processing structured files like CSVs
• Automating repetitive tasks in scripts

🔍 Step-by-Step Breakdown

✅ 5.1 Extract Lines Matching a Pattern with grep

Print all lines containing the word “people”:

grep people usdoi.txt

This shows only the lines where the word people appears.

Print matching lines along with line numbers:

grep -n people usdoi.txt

Count how many lines contain the pattern:

grep -c people usdoi.txt

Ignore case (match both “People” and “people”):

grep -i people usdoi.txt

Show lines that do not contain the pattern:

grep -v login /etc/passwd

Useful for filtering out system-generated accounts from /etc/passwd.

Match only whole words:

grep -w people usdoi.txt

Prevents partial matches like peoples or unpeople.

✅ 5.2 Extract Fields from Lines Using cut

View first two characters of each line in zoo.txt:

cut -c -2 zoo.txt

View text starting from the second character:

cut -c 2- zoo.txt

These options extract by character position, useful for fixed-width formats.

📥 Work with Delimited Files (e.g., CSV)

Download and view the file:

wget https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBM-LX0117EN-SkillsNetwork/labs/v4_new_content/labs/names_and_numbers.csv
cat names_and_numbers.csv

Sample content:

Name,Phone
Alice,555-1234
Bob,555-5678
Charlie,555-9012

Extract just the phone numbers (second field):

cut -d "," -f2 names_and_numbers.csv

• -d "," tells cut to split on commas
• -f2 tells it to return the second field

Output:

Phone
555-1234
555-5678
555-9012

You can also extract multiple fields:

cut -d "," -f1,3 names_and_numbers.csv

Returns fields 1 and 3 — useful when skipping unnecessary columns.

📋 Summary Table

🧠 Why These Tools Matter

They’re often used together in pipelines:

grep "New York" contacts.csv | cut -d "," -f2

This finds all entries for New York and extracts their phone numbers.

🧩 Exercise 6 - Basic Text Wrangling: Merging Lines as Fields

In this exercise, you learned how to use the paste command to merge lines from multiple files side-by-side, like combining columns in a spreadsheet.

This is especially useful when:

• You’re working with related data stored in separate files
• You want to align rows for analysis or reporting
• You need to build structured output from flat files

🔧 Step-by-Step Breakdown

✅ Download an additional file:

wget https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBM-LX0117EN-SkillsNetwork/labs/module%201/zoo_ages.txt

You already have zoo.txt, which contains animal names. Now zoo_ages.txt has corresponding age data.

✅ Merge both files line-by-line using paste:

paste zoo.txt zoo_ages.txt

By default, paste uses a Tab (\t) character to separate merged fields.

Example Output:

lion	5
tiger	4
zebra	6
elephant	10

This makes it easy to combine related data into a single view.

✅ Change the Delimiter to Comma (,) for CSV-like Output:

paste -d "," zoo.txt zoo_ages.txt

Now the output looks like:

lion,5
tiger,4
zebra,6
elephant,10

💡 This is useful for creating CSV files or preparing data for scripts and databases.

You can also use other delimiters like space, colon, or semicolon:

paste -d " " zoo.txt zoo_ages.txt   # Space
paste -d ":" zoo.txt zoo_ages.txt  # Colon

📋 Summary Table

🧠 Why paste Is Useful

🛠️ Try It Out – Real-World Examples

Combine Names and Ages into One File:

paste -d "," zoo.txt zoo_ages.txt > animals.csv

Creates a new file animals.csv that’s ready for import into Excel or a database.

Merge Multiple Files:

paste names.txt emails.txt phones.txt

Merges three files — one per column — ideal for building contact lists.

🛠️ Practice Exercises – Text Processing in Linux

These hands-on exercises help reinforce your knowledge of file inspection, searching, and text manipulation using essential Linux commands like wc, grep, head, tail, cut, and more.

🔧 Before You Begin

Make sure you’re in your home directory:

cd ~
pwd

📝 Practice Exercise Solutions

1. Display the number of lines in /etc/passwd

✅ Solution:

wc -l /etc/passwd

This shows how many user accounts exist on the system (each line in /etc/passwd represents a user).

2. Display lines containing “not installed” in /var/log/bootstrap.log

✅ Solution:

grep "not installed" /var/log/bootstrap.log

This helps identify packages or services that failed to install during system boot.

3. Find websites with “org” in them from top-sites.txt

First, download the file:

wget https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBM-DB0250EN-SkillsNetwork/labs/Bash%20Scripting/top-sites.txt

✅ Use grep to search for “org”:

grep "org" top-sites.txt

This lists all URLs or domains that include “org”.

🔄 Alternative solution using case-insensitive match:

grep -i "org" top-sites.txt

Useful if you want to catch both “org” and “ORG”, etc.

4. Print the first 7 lines of top-sites.txt

✅ Solution:

head -7 top-sites.txt

This gives a quick preview of the top sites list.

5. Print the last 7 lines of top-sites.txt

✅ Solution:

tail -7 top-sites.txt

Handy when you’re interested in newer entries at the end of a list or log file.

6. Print the first three characters of each line from top-sites.txt

✅ Solution:

cut -c -3 top-sites.txt

This extracts only the first 3 characters from every line — useful for fixed-width data or codes.

7. Extract and view only the names from names_and_numbers.csv

Assuming the file already exists:

cat names_and_numbers.csv

✅ Solution:

cut -d "," -f1 names_and_numbers.csv

• -d "," tells cut to use comma as the delimiter
• -f1 selects the first field — which is the name column

You can also skip the header if needed:

tail -n +2 names_and_numbers.csv | cut -d "," -f1

📋 Summary Table: Commands Used

🧠 Why These Skills Matter

You now have the tools to:

• Analyze logs
• Filter and extract data
• Process CSVs and structured files
• Build automation pipelines using command-line tools

These are foundational skills for scripting, system administration, and data analysis in Linux.

Exercise 7 – Combining Commands with Pipes and Redirection

In this exercise, you’ll learn how to:

• Combine multiple Linux commands using pipes (|)
• Redirect command output to files using > and >>
• Use input redirection with <
• Build powerful command pipelines that process data step-by-step

These skills are essential for:

• Automating repetitive tasks
• Processing logs or large datasets
• Writing shell scripts
• Becoming a more efficient Linux user

🔧 What is Piping?

The pipe operator (|) takes the output of one command and feeds it as input to another.

This lets you chain together small tools to build complex operations.

Example:

ls -l | grep "Jan" | wc -l

This pipeline:

1. Lists all files (ls -l)
2. Filters only those modified in January (grep "Jan")
3. Counts them (wc -l)

📥 Input and Output Redirection

You can also control where input comes from and where output goes using:

Example:

grep "error" /var/log/syslog > errors.txt

Saves all lines containing “error” from the system log into a new file.

💡 Hands-On Practice

Let’s go through some guided examples.

✅ 1. Chain grep, sort, and uniq to Analyze Log Data

Find unique IP addresses in an access log:

grep "Failed password" /var/log/auth.log | awk '{print $9}' | sort | uniq

• grep: filters for failed login attempts
• awk: extracts the IP address field
• sort: prepares for deduplication
• uniq: removes duplicates

You’ll learn about awk soon — it’s a powerful text processing tool.

✅ 2. Save Command Output to a File

Save your list of running processes to a file:

ps -e > process_list.txt

Now view it:

cat process_list.txt

✅ 3. Count Words in a File Using a Pipeline

Count how many times each word appears in usdoi.txt:

tr ' ' '\n' < usdoi.txt | sort | uniq -c | sort -nr

What this does:

• tr ' ' '\n': replaces spaces with newlines (puts each word on its own line)
• sort: sorts words alphabetically
• uniq -c: counts occurrences
• sort -nr: sorts numerically in reverse order

✅ 4. View Command Output One Page at a Time

Sometimes output fills your screen. Use less to page through it:

history | less

Use ↑ ↓ keys to scroll, and press q to quit.

📋 Summary Table: Pipes & Redirection

| Task | Command | | ------------------------------ | --------------------- | --------- | | Pipe output to another command | command1 | command2 | | Redirect output to a file | command > file.txt | | Append output to a file | command >> file.txt | | Read input from a file | command < file.txt |

🧠 Why This Matters

With pipes and redirection, you can:

• Automate workflows with simple, reusable components
• Process large amounts of data efficiently
• Build custom scripts that do exactly what you need

🎉 Summary – Great Job Completing the Lab!

You’ve just gained hands-on experience with some of the most essential Linux text processing and file inspection tools. These skills are fundamental for working efficiently in a Linux environment — whether you’re managing logs, analyzing data, or writing shell scripts.

🔍 What You Learned

Here’s a quick recap of the core commands and skills you practiced:

💡 Why This Matters

These tools form the foundation of text-based data manipulation in Linux:

• They allow you to quickly inspect and analyze large files
• You can filter, format, and combine data using simple yet powerful utilities
• Together, they enable pipeline-style scripting (e.g., grep | sort | uniq) — a key part of Linux automation

🧠 Pro Tip: Combine Commands with Pipes!

Now that you know these individual tools, try combining them using the pipe (|) operator:

grep "error" /var/log/syslog | wc -l

Counts how many error messages are in the system log.

Or:

cat top-sites.txt | tail -10 | grep "org" | sort

Gets the last 10 sites, filters for “org”, and sorts alphabetically.

Networking Commands in Linux

1. Introduction

This video introduces essential Linux networking commands that help you:

✅ View your network configuration
✅ Test connectivity to remote servers
✅ Retrieve data from URLs

These tools are invaluable for troubleshooting, automation, and interacting with web services.

2. hostname – Get or Set the Host Name

Purpose

Displays or sets the hostname of the machine — a unique identifier used on the network.

Basic Usage

hostname

Output:

my-linux-machine.local

• .local indicates your system uses zeroconf/local domains (e.g., Bonjour).

Options

3. ifconfig – Interface Configuration

Purpose

Displays or configures network interfaces such as Ethernet (eth0) or Wi-Fi (wlan0).

⚠️ Note: ifconfig is deprecated in many modern Linux distros; use ip addr instead.

Basic Usage

ifconfig

Shows detailed information about all active interfaces including:

• IP Address (inet)
• MAC Address (ether)
• Packets received/transmitted
• Error/dropped packet counts

Example

ifconfig eth0

Shows details only for the Ethernet interface named eth0.

4. ping – Test Network Connectivity

Purpose

Tests whether a host or IP address is reachable by sending ICMP echo requests.

Basic Syntax

ping <hostname_or_ip>

Example

ping google.com

Output:

PING google.com (142.251.41.78): 56 data bytes
64 bytes from 142.251.41.78: icmp_seq=0 ttl=119 time=10.4 ms
...

Useful Options

Example:

ping -c 5 google.com

Returns 5 ping results and summary statistics:

• Number of packets transmitted and received
• Packet loss percentage
• Round-trip times (min/avg/max/stddev)

5. curl – Transfer Data from or to a URL

Purpose

A powerful command-line tool for transferring data using various protocols like HTTP, HTTPS, FTP, etc.

Basic Syntax

curl <url>

Examples

• Download HTML content from Google:

  curl http://www.google.com

• Save output to a file:

  curl -o google.html http://www.google.com

Common Uses

• Testing API endpoints
• Downloading files/scripts
• Sending HTTP requests with custom headers/data

6. wget – Retrieve Files from Web URLs

Purpose

Downloads files from the web recursively and supports resuming broken downloads.

Basic Syntax

wget <url>

Example

Download a test file from W3.org:

wget https://www.w3.org/TR/2002/REC-xml-20021104/ISO-Latin-1-encoding.txt

Output Includes

• Resolving host
• Connecting to server
• Sending HTTP request
• Saving file locally (with original name by default)

Useful Options

Example:

wget -O iso.txt https://www.w3.org/TR/2002/REC-xml-20021104/ISO-Latin-1-encoding.txt

7. Summary Table of Networking Commands

8. Final Tips

• Use hostname and ifconfig to quickly check your machine’s identity and network status.
• Use ping to test connection stability to a website or IP address.
• Use curl for quick data transfer and testing APIs.
• Use wget for downloading files, especially when working offline or scripting.

9. Bonus: Modern Alternative to ifconfig – ip Command

While ifconfig is widely known, it’s being replaced by the more powerful ip command suite:

🌐 A Brief Introduction to Networking – Summary & Highlights

Great job reading through this foundational networking guide! This optional but valuable reading introduced you to core concepts in computer networking, helping you understand how computers communicate, share resources, and connect across networks like the Internet.

🎯 Learning Objectives Recap

After completing this reading, you are now able to:

✅ Describe computer networks, network resources, and network nodes
✅ Explain the roles of hosts, clients, and servers
✅ Understand what packets and pings are
✅ Differentiate between URLs and IP addresses

🧩 Key Concepts Explained

🔹 Computer Networks

• A computer network is a collection of interconnected devices that can communicate and share resources.
• Examples:
  • LAN (Local Area Network) – small, localized network (e.g., home or office)
  • WAN (Wide Area Network) – covers large geographical areas (e.g., the internet)
  • The Internet – a global network of networks

💡 The internet is essentially a network of computer networks.

🔁 Hosts, Clients, and Servers

💡 Many devices can switch roles — acting as both client and server when needed.

📦 Packets and Pings

What Is a Network Packet?

• A packet is a formatted unit of data sent over a network.
• Contains:
  • Control information: source, destination, routing info
  • Payload: actual data being transmitted

What Is ping?

• A utility used to test connectivity between two hosts
• Works by sending an “echo request” packet and waiting for a response
• Helps diagnose connection issues (e.g., “Can I reach Google’s servers?”)

Example command:

ping google.com

🌍 URLs and IP Addresses

What Is an IP Address?

• Stands for Internet Protocol Address
• A unique identifier assigned to each device connected to a network
• Used to locate and communicate with other devices
• Example IPv4 address: 192.168.1.1
• Example IPv6 address: 2001:0db8:85a3::8a2e:0370:7334

💡 When you use ping, it uses IP addresses to send and receive packets.

What Is a URL?

• Stands for Uniform Resource Locator
• Also known as a web address
• Identifies the location of a resource on the internet and how to access it

URL Format:

protocol://hostname/path

Example:

https://en.wikipedia.org/wiki/URL

Breakdown:

• Protocol: https – method to retrieve the resource
• Hostname: en.wikipedia.org – server where the resource lives
• Path: /wiki/URL – specific file/resource on the server

📌 URLs make it easier for humans to access resources without needing to remember complex IP addresses.

🧠 Why These Concepts Matter

Understanding these basics helps you:

• Troubleshoot network issues using commands like ping
• Understand how computers communicate over the internet
• Work more effectively with web-based tools and services
• Prepare for deeper learning about Linux networking commands

✅ Summary Table

🧾 Exercise 1 – View Configuration Info About Your Network

In this exercise, you learned how to view your system’s network configuration, including:

• Hostname
• IP address
• Network interface details using hostname and ip

This is essential for understanding how your machine connects to the network and communicates with other systems.

🔍 Overview of What You Learned

✅ Step-by-Step Breakdown

🔹 1.1 Display Your System’s Hostname and IP Address

View the current hostname:

hostname

Example output:

theia-2c65847f

The hostname helps identify your machine on a network — especially useful in server environments.

View the system’s IP address:

hostname -i

Example output:

172.17.0.2

💡 This shows the IPv4 address associated with your host.

🔹 1.2 Display Network Interface Configuration

Before running the ip command, you installed the iproute2 package:

Update and install:

sudo apt update
sudo apt install iproute2

Now you can use the powerful ip command.

Show all network interfaces:

ip a

or

ip addr

This displays information like:

• Interface name (lo, eth0, etc.)
• IP addresses (inet, inet6)
• MAC address (link/ether)
• Status (UP, DOWN)

Example output line:

inet 172.17.0.2/16 brd 172.17.255.255 scope global eth0

Here, 172.17.0.2 is your IPv4 address.

Show configuration for a specific interface (like eth0):

ip addr show eth0

📌 eth0 is typically the primary Ethernet interface used to connect to the network.

You’ll see:

• The device status (UP)
• Its IPv4 and IPv6 addresses
• Broadcast and subnet mask info

📋 Summary Table: Useful Commands

🧠 Why These Tools Matter

Understanding your network configuration helps with:

• Troubleshooting connectivity issues
• Configuring servers
• Monitoring network usage
• Writing scripts that depend on network state

The ip command is a modern replacement for older tools like ifconfig, and it offers more flexibility and control.

🛠️ Real-World Use Cases

🧪 Exercise 2 – Test Network Connectivity with ping

In this exercise, you learned how to use the ping command to test whether your system can successfully communicate with another device or website over the network.

This is a fundamental tool for:

• Checking internet connectivity
• Diagnosing network issues
• Testing server availability

🔍 Overview of What You Learned

✅ Step-by-Step Breakdown

🔹 2.1 Test Connectivity to a Host Using ping

Ping Google continuously:

ping www.google.com

You’ll see output like:

64 bytes from 142.251.42.78: icmp_seq=1 ttl=115 time=15.3 ms
64 bytes from 142.251.42.78: icmp_seq=2 ttl=115 time=14.9 ms
...

Each line shows:

• The size of the response
• The IP address of the responding server
• Sequence number
• Time-to-live (TTL)
• Round-trip time in milliseconds

⚠️ To stop the ping process, press Ctrl + C

Ping a Host a Specific Number of Times

To limit the number of packets sent, use the -c option:

ping -c 5 www.google.com

This sends exactly 5 packets, then stops automatically.

Useful for:

• Scripting and automation
• Quick tests without manually stopping the command

📋 Summary Table

🧠 Why This Matters

Using ping helps you quickly determine:

• Whether you have internet access
• If a remote server is online
• How fast your connection is (based on response time)
• If there’s packet loss or high latency

It’s one of the most basic yet powerful tools in any Linux user’s networking toolkit.

🛠️ Real-World Use Cases

📥 Exercise 3 – View or Download Data from a Server

In this exercise, you learned how to retrieve data from remote servers using two powerful command-line tools:

• curl – for transferring data and viewing content directly in the terminal
• wget – for downloading files (and even entire websites)

These tools are essential for:

• Fetching configuration files
• Downloading software or scripts
• Interacting with APIs
• Automating tasks that involve remote data

🔍 Overview of What You Learned

✅ Step-by-Step Breakdown

🔹 3.1 Transfer Data from a Server Using curl

View file contents from a URL:

curl https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBM-DB0250EN-SkillsNetwork/labs/Bash%20Scripting/usdoi.txt

This displays the full text of the U.S. Declaration of Independence directly in your terminal.

💡 This is useful when you want to inspect remote files without saving them.

Save the file to your current directory:

curl -O https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBM-DB0250EN-SkillsNetwork/labs/Bash%20Scripting/usdoi.txt

Now you have a local copy named usdoi.txt.

📁 The -O option tells curl to save the file using its original filename.

🔹 3.2 Download Files Using wget

First, remove the file if it already exists:

rm usdoi.txt

Then download it again using wget:

wget https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBM-DB0250EN-SkillsNetwork/labs/Bash%20Scripting/usdoi.txt

This downloads the file and saves it in your current directory.

⚙️ wget is especially useful because:

• It works well in scripts
• Supports recursive downloads (-r)
• Can continue interrupted downloads (-c)
• Doesn’t require user interaction once started

📋 Summary Table: curl vs wget

🧠 Why These Tools Matter

With curl and wget, you can:

• Automate downloads in scripts
• Fetch live data from APIs or web services
• Download large datasets or software packages
• Troubleshoot HTTP responses and server connectivity

They’re foundational tools for working with networked resources in Linux.

🛠️ Real-World Examples

🔽 Download a file silently with wget:

wget -q https://example.com/file.zip

🖥️ Download and display JSON from an API:

curl https://api.github.com/users/octocat

📂 Recursively download an entire website:

wget -r https://example.com

📥 Resume a partially downloaded file:

wget -c http://example.com/largefile.iso

Exercise 4 – Exploring DNS and Looking Up Domain Information

In this exercise, you’ll learn how to:

• Understand what DNS is and why it matters
• Use nslookup and dig to look up domain information
• Check IP addresses, name servers, and mail servers associated with a domain

These tools are essential for:

• Troubleshooting domain issues
• Checking website availability
• Understanding how domains resolve to IP addresses
• Debugging email delivery problems using MX records

🌐 What Is DNS?

DNS (Domain Name System) is like the phonebook of the internet.

It maps human-readable domain names (like google.com) to machine-readable IP addresses (like 172.217.174.78), so your computer knows where to find a website or service.

Key DNS Concepts:

🔍 Step-by-Step: Using nslookup

The nslookup command helps you query DNS servers to get domain-related information.

✅ View Basic DNS Info for a Website

nslookup google.com

This shows:

• The IP address of the domain
• The DNS server used to retrieve the info

✅ Look Up Mail Servers (MX Records)

nslookup -type=mx gmail.com

This lists the mail exchange (MX) servers responsible for receiving emails for gmail.com.

✅ Query Name Servers (NS Records)

nslookup -type=ns ibm.com

This shows which name servers are responsible for managing the domain’s DNS records.

🔎 Step-by-Step: Using dig

dig (Domain Information Groper) is a more detailed and powerful tool than nslookup. It gives you full control over DNS queries.

✅ View A Record for a Domain

dig google.com

Look for the ANSWER SECTION:

google.com.     299     IN      A       172.217.174.78

This shows the IPv4 address that google.com resolves to.

✅ Look Up MX Records with dig

dig MX gmail.com

Scroll down to the ANSWER SECTION to see which servers handle email for Gmail.

✅ Get All DNS Records for a Domain

dig ANY ibm.com

This fetches all available DNS records for ibm.com, including:

• A / AAAA
• CNAME
• MX
• NS
• TXT (used for SPF, DKIM, etc.)

⚠️ Some domains may restrict “ANY” queries for security reasons.

📋 Summary Table: Useful DNS Commands

🧠 Why This Matters

Understanding DNS helps you:

• Diagnose domain resolution issues
• Verify email server settings
• Configure custom domains
• Troubleshoot website downtime

Tools like nslookup and dig are invaluable for system administrators, developers, and anyone working with web services.

🛠️ Real-World Examples