Linux OS Shell: Google Cybersecurity Certificate 4/9

The third submodule of Module 2: Linux Operating System covers the Shell. The topics covered in this write-up are:

Introduction to Shell

Types of Shells

Using the Shell

Lab Activity

1- Introduction to Shell:

The shell is a command- line interpreter between the user and the operating system.

It is like a translator that translates the commands that the user enters (on the interface), into the language that the OS kernel understands, that is, Machine Language.

An example of commands on the shell would be:

Bash is one of the shells in Linux

Not only are there different types of Linux distributions, but there are also different types of shells.

2- Types of Shells:

• Bash:

Bash, the Bourne Again Shell, is the default Linux shell and is most commonly used. It uses the $ prompt to indicate it is ready to accept commands.

prompt for commands

Some of the other shells are:

• C Shell (csh)
• Korn Shell (ksh)
• Enhanced C shell (tcsh)
• Z Shell (zsh)

3- Using the Shell:

• Input, Output, and Errors

The commands that the user types into the shell are called input. The shell then interprets it and asks the kernel for the resources in order to get those tasks done. Then gives the user output. A simple input-output scenario would be:

On the other hand, if the user intentionally misspells a word, or tries to run a command he is not allowed to, the shell can give an error message. For example:

Additionally, it also gives suggestions alternative to the written command.

4- Lab Activity:

The following tasks were performed as part of lab activities.

Task 1. Generate output with the echo command

The following outputs were generated:

Task 2. Generate output with the expr command

The following outputs were generated:

The expr command performs basic mathematical calculations.

Here, the numbers and the operators must be separated by a space in order for the correct output to be displayed.

Task 3. Clear the Bash shell

The following outputs were generated:

Today, I learnt how to:

• generate output with the echo command
• generate output with the expr command
• clear the Bash shell with the clear command