2.1 Command Line Basics (Weight: 3)

📘Linux Essentials (LPI 010-160)

This topic is very important for the Linux Essentials exam. You must clearly understand what a shell is, how commands are written, and how the command line works.

This section explains everything in simple English so that both IT and non-IT learners can understand easily.

1. What is the Shell?

The shell is a program that allows users to interact with the Linux system by typing commands.

It works as a bridge between:

The user
The Linux kernel

The shell:

Reads your command
Understands it
Tells the system what to do
Shows the output

Without the shell, you cannot use the command line.

2. What is a Terminal?

A terminal is a program that gives you access to the shell.

In a graphical desktop environment, you open a terminal application to:

Type commands
Manage files
Install software
Configure services
Check system status

The terminal shows a prompt like this:

user@hostname:~$

This is called the shell prompt.

3. Popular Linux Shells

There are different shell programs in Linux.

The most common shell is:

Bash

Bash stands for:

Bourne Again Shell

Other shells exist, but for the exam, you mainly focus on Bash.

You can check your current shell with:

echo $SHELL

4. Basic Structure of a Command

Every Linux command follows a simple structure:

command [options] [arguments]

Let’s understand each part clearly.

4.1 Command

The command is the program you want to run.

Examples:

ls
pwd
mkdir
cp

Each command performs a specific task.

4.2 Options (Flags or Switches)

Options modify how a command works.

They usually start with:

A single dash: -
Or double dash: --

Examples:

ls -l
ls -a
ls -la

-l → long listing format
-a → show hidden files

Options can be combined:

ls -la

This means:

-l
and -a

Some commands use long options:

ls --all

4.3 Arguments

Arguments tell the command what to work on.

Example:

ls /home

ls → command
/home → argument (directory)

Another example:

mkdir project

mkdir → command
project → argument (new directory name)

5. Case Sensitivity in Linux

Linux is case-sensitive.

This means:

file.txt
File.txt
FILE.txt

All three are different.

Commands are also case-sensitive:

ls   ✓ correct
LS   ✗ wrong

For the exam, always remember:

Linux treats uppercase and lowercase differently.

6. Types of Commands

There are three main types of commands:

6.1 Internal Commands

These are built into the shell.

Examples:

cd
echo
pwd

They run directly inside Bash.

6.2 External Commands

These are separate programs stored in system directories.

Examples:

ls
cp
mv

They are stored in directories like:

/bin
/usr/bin

You can check where a command is located:

which ls

6.3 Aliases

Aliases are shortcuts for commands.

Example:

alias ll='ls -l'

Now typing:

ll

Runs:

ls -l

To see all aliases:

alias

7. Getting Help in the Shell

Very important for the exam.

Linux provides built-in help systems.

7.1 –help Option

Most commands support:

command --help

Example:

ls --help

7.2 Man Pages

Manual pages show detailed documentation.

man ls

To search inside man:

Press /
Type word
Press Enter

To exit:

7.3 Info Pages

Some programs use:

info command

Example:

info ls

8. Running Multiple Commands

You can combine commands in different ways.

8.1 Run One After Another (Always)

command1 ; command2

Example:

mkdir test ; cd test

Both commands run, even if the first fails.

8.2 Run Only if First Succeeds

command1 && command2

Second runs only if first is successful.

Used often in:

Software installation
Service configuration

8.3 Run if First Fails

command1 || command2

Second runs only if first fails.

9. Command History

The shell stores previous commands.

Use:

history

To run a previous command:

!number

Example:

!45

Runs command number 45.

Use arrow keys:

Up arrow → previous command
Down arrow → next command

10. Wildcards (Globbing)

Wildcards help match multiple files.

10.1 Asterisk (*)

Matches multiple characters.

ls *.txt

Shows all files ending with .txt.

10.2 Question Mark (?)

Matches exactly one character.

ls file?.txt

Matches:

file1.txt
fileA.txt

10.3 Square Brackets []

Matches specific characters.

ls file[123].txt

Matches:

file1.txt
file2.txt
file3.txt

11. Quotes in Linux

Quotes are very important in command syntax.

11.1 Double Quotes (” “)

Allow variable expansion.

Example:

echo "My home is $HOME"

11.2 Single Quotes (‘ ‘)

Prevent variable expansion.

echo 'My home is $HOME'

Prints exactly:

My home is $HOME

12. Variables in the Shell

A variable stores a value.

Example:

name=admin

To use it:

echo $name

Environment variables:

echo $HOME
echo $PATH

13. Special Characters

Some characters have special meaning:

>   redirect output
<   redirect input
|   pipe output
&   run in background

Example:

ls > files.txt

This saves output into a file.

14. Exit Status (Very Important for Exam)

Every command returns an exit status.

0 → success
Non-zero → error

Check exit status:

echo $?

This is very important in scripting and automation.

15. Root User and Permissions

Some commands require administrator privileges.

To run as root:

sudo command

In IT environments:

Used to install software
Modify system configuration
Restart services

16. Tab Completion

Press:

Tab

It:

Auto-completes commands
Auto-completes file names
Reduces typing errors

Very useful in real IT work environments.

17. Clearing the Screen

clear

Or:

Ctrl + L

18. Important Exam Points Summary

For the LPI 010-160 exam, you must know:

✔ What a shell is
✔ What Bash is
✔ Command structure (command + options + arguments)
✔ Difference between internal and external commands
✔ How to get help (man, –help)
✔ Wildcards (*, ?, [])
✔ Command history
✔ Exit status ($?)
✔ Variables and quoting
✔ Command chaining (;, &&, ||)
✔ Case sensitivity
✔ Tab completion

Final Notes for Students

Understanding the command line is the foundation of Linux administration.

In IT environments, system administrators use the shell to:

Manage servers
Configure services
Automate tasks
Monitor system performance
Install and manage software
Troubleshoot issues

The shell is powerful, fast, and efficient.

For the exam, focus on:

Syntax
Structure
Behavior of commands
Understanding output

If you master this topic, you build a strong base for the rest of Linux Essentials.