Week 1 Discussion - Unix and Command Line Basics

Introduction

Exercise 23

How will the Unix shell and programming language Bash help us?

Solution to

using Bash we can connect many pieces of software together. For example, we can redirect the output of a program to another. The Unix shell also contains many small software tools which ease working with files.

What is Unix?

Exercise 24

What is Unix?

Solution to

Unix is an operating system which is different than the widely used Windows. The first Unix was developed in 1969 and we have nowadays many operating systems which are based on the concepts of the first Unix, e.g., tree-based file system, shell or everything is a file

Exercise 25

Where did you see a shell (command-line interface) before?

Solution to

• e.g., in the film Matrix or other films which feature computer hackers

• at the airport when dropping off the luggage at a counter. The staff sometimes uses a command-line interface to enter passenger data

Exercise 26

what are other words for shell?

Solution to

• command-line interface

• console

Note that in this book shell is depicted only as a command line interface. In general, shell is an interface to the operating system and it can be both graphical or text-based [1]

Exercise 27

The shell is a very direct and powerful way to manipulate a computer. … or you can wreak havoc on yourself and on others. …

Do you have an example for such a command?

Solution to

sudo rm -rf /

Getting Unix

Exercise 28

Which did/would you use to get a Unix shell?

A) Mac A) Windows WSL A) Windows + Virtualbox + Ubuntu A) cloud A) other

Command Line basics

Exercise 29

Which command allows to you to clear the shell?

Solution to

clear

There is also a shortcut: CTRL + L

Exercise 30

What is the command-line prompt?

Solution to

For example:

alena:~ inf1$

Same like the literal meaning, this line prompts you to enter a command.

Exercise 31

Which is the typical structure of commands?

A) command - options - arguments A) command - arguments - options A) arguments - command - options A) options - command - arguments A) I don’t know

Solution to

For example:

echo -n hello

Another examples:

grep -e AGCT -e AGTT reads.txt
ls myfolder -l  # also works

Exercise 32

• How can you reexecute the commands that you used before?

• What if you are searching for a command that you used very long ago?

Solution to

• Up and Down keys.

• It is also possible to search for a command using Ctrl+R. Press Ctrl+R and type a part of the command that you used before. Then press CTRL+R again to jump to the next.

  Alternatively you can view the history file of your shell, e.g., .bash_history in bash or .histfile in zsh.

Exercise 33

Browse

• ireaneus/linux-cheat-sheets or

• github.com/sudheerj/Linux-cheat-sheet

Pick a command that you never seen before. If you find the command useful, prepare a one minute presentation of the command. Post your command on the chat so that everyone can present another command. You can share your screen to present the command.

Exercise 34

You want to prepare the following directory structure on your home folder:

photos/2022
photos/2021
documents/

You start creating the directories:

mkdir photos/2022

But get the following error:

mkdir: cannot create directory ‘photos/2022’: No such file or directory

1. What could be the reason? In other words, what does the error message mean?

2. How could you fix this?

Solution to

1. It means that a file or directory does not exist, so the command fails. In this case the missing thing is the directory photos. mkdir cannot create 2022, because the parent directory photos does not exist.

2. We could first mkdir photos, then mkdir photos/2022. There is an easier way though. From man mkdir:

   -p, --parents no error if existing, make parent directories as needed …

   So using -p creates all the parent directories if required.

Exercise 35

1. What is the problem with the following command sequence?

   %%sh
   cd /tmp
   # use /tmp as a playground (files in /tmp are deleted after reboot)
   
   echo carrots > shopping-list.txt
   echo thyme > shopping-list.txt
   echo parsley > shopping-list.txt
   

2. How can we avoid/undo our mistake?

Solution to

1. The file gets overwritten instead of appended.

2. There is no undo for > or >> operation. We could regularly backup our files, but the better solution is that we become more cautious when using these kind of commands.

For more info browse the section Migration and Destruction

Final reflection

Exercise 36

Did you reach the following learning objectives for this week? Discuss with your partner.

• Describe Unix

• Install and/or access Bash

• Execute basic commands in the command line

• Create and manipluate directories

• Inspect, move, copy, and delete files and folders

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WP: Shell_(computing)