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Module 01 - Command Line Fundamentals

Estimated time: 60–90 minutes

Prerequisites: - Module 00 – Introduction to Linux

Difficulty: Beginner

Hands-on exercises: Yes

Overview

The Linux command line is one of the most powerful tools available to a system administrator. While many operating systems provide graphical interfaces, Linux administration is primarily performed from the command line.

Learning the command line allows you to:

  • Work efficiently
  • Manage remote servers
  • Troubleshoot systems
  • Automate repetitive tasks
  • Manage thousands of files quickly
  • Perform administration without a graphical interface

This module introduces the Linux shell, explains how commands are structured, and teaches you how to move around the Linux filesystem confidently.

Learning Objectives

By the end of this lesson you will be able to:

  • Explain what the Linux shell is.
  • Understand the Linux command prompt.
  • Recognise the structure of a Linux command.
  • Display your current working directory.
  • Navigate around the filesystem.
  • List files and directories using different options.

What is the Linux Shell?

The shell is a program that accepts commands from the user and passes them to the Linux kernel for execution.

Think of it as an interpreter between you and the operating system.

+---------------------+
|      User           |
+---------------------+
          |
          v
+---------------------+
|      Shell          |
|      (Bash)         |
+---------------------+
          |
          v
+---------------------+
|   Linux Kernel      |
+---------------------+
          |
          v
+---------------------+
|     Hardware        |
+---------------------+

The shell performs many useful functions including:

  • Running programs
  • Managing files
  • Launching applications
  • Executing scripts
  • Redirecting output
  • Automating repetitive tasks

The most common shell is Bash (Bourne Again SHell), although others exist such as:

  • Zsh
  • Fish
  • Korn Shell (ksh)
  • C Shell (csh)

To see which shell you are using, run:

echo $SHELL

Example output:

/bin/bash

Understanding the Command Prompt

When you log into a Linux system you will normally see something similar to:

james@k3s-node-01:~$

This is known as the command prompt.

Let's break it down.

james @ k3s-node-01 : ~ $
│         │           │
│         │           └── Current directory
│         └────────────── Hostname
└──────────────────────── Username

The final character is important:

$

indicates a standard user.

Whereas:

#

indicates the root user.

Always check your prompt before running administrative commands.

The Current Working Directory

Linux always keeps track of where you are in the filesystem.

This location is called the Current Working Directory (CWD).

To display it, use:

pwd

Example:

/home/james

If you are in another directory:

/etc

then:

pwd

returns:

/etc

Knowing your current location is important because many commands work relative to your current directory.

Listing Files and Directories

The ls command displays the contents of a directory.

Basic usage:

ls

Example output:

Documents
Downloads
Pictures
projects

Long Listing

To display more information:

ls -l

Example:

drwxr-xr-x 2 james users 4096 Jul 18 Documents
-rw-r--r-- 1 james users  245 Jul 20 notes.txt

This shows:

  • File permissions
  • Number of links
  • Owner
  • Group
  • File size
  • Date modified
  • File name

Show Hidden Files

Files beginning with a full stop (.) are hidden by default.

Display them with:

ls -a

Example:

.
..
.bashrc
.profile
Documents
Downloads

Human Readable Sizes

ls -lh

Example:

-rw-r--r-- 1 james users 2.4K notes.txt

Instead of displaying file sizes in bytes, -h shows them in a human-readable format such as KB, MB or GB.

Navigating the Filesystem

Use the cd command to change directories.

Move to your home directory:

cd

or

cd ~

Move to another directory:

cd /etc

Check where you are:

pwd

Example:

/etc

Moving Up One Directory

Use:

cd ..

Example:

If you are in:

/home/james/projects

running:

cd ..

takes you to:

/home/james

Returning to the Previous Directory

Use:

cd -

Example:

/home/james

↓

cd /etc

↓

cd -

returns you to:

/home/james

Going to the Root Directory

To move to the top of the Linux filesystem:

cd /

Verify your location:

pwd

Output:

/

Absolute vs Relative Paths

Linux understands two types of paths.

Absolute Path

An absolute path always starts at the root directory (/).

Example:

/home/james/projects/basic-linux-training

No matter where you are currently located, this path always points to the same location.

Relative Path

A relative path starts from your current location.

For example, if your current directory is:

/home/james

then:

cd projects

works because projects exists beneath your current directory.

Visual Example

/

├── home
│   └── james
│       └── projects
│           └── basic-linux-training
│
├── etc
├── var
└── usr

If you are in:

/home/james

then:

cd projects/basic-linux-training

is a relative path.

Whereas:

cd /home/james/projects/basic-linux-training

is an absolute path.

Best Practices

✔ Check your current location with pwd before making changes.

✔ Use ls -l when you need detailed file information.

✔ Prefer absolute paths when writing scripts.

✔ Use cd ~ to quickly return to your home directory.

✔ Be aware of whether you are a standard user ($) or the root user (#).

Summary

In this lesson you learned:

  • What the Linux shell is.
  • How the command prompt is structured.
  • How commands are entered.
  • How to identify your current directory.
  • How to navigate the filesystem.
  • The difference between absolute and relative paths.

In Part 2, you will learn how to create, copy, move and delete files and directories safely.