Bash scripting

Question 1

What are the layers of an OS?

Answer 1

The Outer “Shell”

Shell - Commands - apps - scripts

Network service - libraries - file systems - frameworks

Sys.calls - device drivers

Kernel

Question 2

What is a shell?

Answer 2

The outer layerof an OS, where users interact through a graphics-based or text based interface

Question 3

What is bash?

Answer 3

A command line shell

A program that executes commands on the user’s behalf

Question 4

What user has UID 0?

Answer 4

Root (superuser)

Question 5

What does # and $ mean in shell?

Answer 5

When the shell displays a $, it means it is waiting for the user to pass a command.

means the user that is running the shell, is the root user (superuser with administrative rights)

Question 6

What is the “date” command?

Answer 6

Displays the current date

Question 7

What is the “pwd” command?

Answer 7

Print working directory

Question 8

What is the “ls” and “ls -l” commands

Answer 8

list, and long listing

Prints content of working directory

Question 9

What is the “echo” command?

Answer 9

Prints a string or value of a variable to stdout

Question 10

What is the first line of a bash script?

Answer 10

!/bin/bash

Shebang: Acombination of bash (#) and bang (!), followed by the bash shell path

Question 11

What does shebang do?

Answer 11

Tells the shell to execute the script via bash shell

Question 12

What is shebang?

Answer 12

An absolute path to the bash interpreter

Question 13

What command can be used to find the bash shell path?

Answer 13

which bash

Question 14

What is the difference between !¤$ and $_ in the following commands:

mkdir folder && cd !$
mkdir folder && cd $_

Answer 14

!$ gives the last argument of the previous command in the shell history, in this case, the command that was passed to the shell before the mkdir command.

$_ gives the last argument of the previous command, in this case, the argument of mkdir

Question 15

What does the comman “read var_name” do?

Answer 15

Reads input and stores the input value in the following variable, in this case var_name

Question 16

How are variables assigned in bash?

Answer 16

1. Assign value directly: country=Norway
2. Command substitution:
   same_country=$country

Question 17

What is command substitution?

Answer 17

Get a value based on the output obtained from a program or command.

$ is required to access an existing variable’s value

Question 18

How can variables be accessed in bash?

Answer 18

Appending $ to the variable name: $country_name

Question 19

What does $1, $2, and so on mean in bash?

Answer 19

The first, second, and so on, argument that was passed to the function.

Question 20

What command can you use to redirect output from a command and writing it to a file.

Answer 20

ls > output.txt

Question 21

What command can you use to append output from a command to a file.

Answer 21

ls&raquo_space; output_log.txt

Question 22

What is the touch command?

Answer 22

Creates a new file, if name does not exist

Question 23

What command removes a file or directory?

Answer 23

rm

Question 24

What command copies a file or directory?

Answer 24

cp

Question 25

What command moves or renames a file or directory?

Answer 25

mv

Question 26

What is the grep command?

Answer 26

Searches for a pattern in a file

Question 27

What is the df command?

Answer 27

Displays the amount of disk space available

Question 28

What is the history command?

Answer 28

Displays a list of previously executed commands

Question 29

What is the ps command?

Answer 29

Displays information about running processes

Question 30

What is the OR operator in bash?

Answer 30

-o

Question 31

What is the AND operator in bash?

Answer 31

-a

Question 32

What is Cron?

Answer 32

A utility used for job scheduling.
Can be configured to set up automated jobs to run daily, weekly, monthly, or specific time basis.

Question 33

What is crontab?

Answer 33

Used to add and edit cron jobs

Question 34

What command is used to list already scheduled scripts for a user?

Answer 34

crontab -l

Question 35

What command is used to add and edit the cron?

Answer 35

crontab -e

Question 36

How is debug enabled in bash?

Answer 36

Add “set -x” at the beginning of a script (after shebang #!)

Question 37

What does set -x do in a script?

Answer 37

Enable debug, causing bash to print each command that it executes to the terminal, preceded by a + sign

Question 38

How can you check the exit code of the most recent command?

Answer 38

Print the $? variable

e.g.:
echo $?

Question 39

What exit code does a command have on success?

Answer 39

0

Question 40

What does set -e do?

Answer 40

When added to the beginning of a script, when a command in the script fails, bash will exit immediately.