Bash Scripting

Question 1

What is GNU Bourne-Again Shell (Bash)?

Answer 1

It’s a powerful work environment and scripting engine. A competent security professional skillfully leverages Bash scripting to streamline and automate many Linux tasks and procedures.

Question 2

How to create a simple ‘Hello World’ Bash script?

Answer 2

#!/bin/bash
# Hello World Bash Script
echo "Hello World!"

Question 3

How to declare a variable “first_name” as “Kacper”.

Answer 3

kali@kali:~$ first_name=Kacper

Question 4

How to display “first_name” variable using Bash?

Answer 4

kali@kali:~$ echo $first_name

Question 5

How to use of command substitution (whoami) and variables?

Answer 5

user=$(whoami)

user=whoami

Question 6

How to instruct bash to print additional debug output, so we could more easily see the commands that were executed and their results.

Answer 6

!/bin/bash -x

Question 7

Describe special Bash variable ‘$0’

Answer 7

The name of the Bash script

Question 8

Describe special Bash variable ‘$1 - $9’

Answer 8

The first 9 arguments to the Bash script

Question 9

Describe special Bash variable ‘$#’

Answer 9

Number of arguments passed to the Bash script

Question 10

Describe special Bash variable ‘$@’

Answer 10

All arguments passed to the Bash script

Question 11

Describe special Bash variable ‘$?’

Answer 11

The exit status of the most recently run process

Question 12

Describe special Bash variable ‘$$’

Answer 12

The exit status of the most recently run process

Question 13

Describe special Bash variable ‘$USER’

Answer 13

The username of the user running the script

Question 14

Describe special Bash variable ‘$HOSTNAME’

Answer 14

The hostname of the machine.

Question 15

Describe special Bash variable ‘$RANDOM’

Answer 15

A random number.

Question 16

Describe special Bash variable ‘$LINENO’

Answer 16

The current line number in the script

Question 17

How to collect user input using read “answer”?

Answer 17

!/bin/bash

echo “Hello there, would you like to learn how to hack: Y/N?”
read answer
echo “Your answer was $answer”

Question 18

What ‘-p’ option do in read command?

Answer 18

Allows to specify a prompt.

Question 19

What ‘-s’ option do in read command?

Answer 19

Makes the user input silent. The latter is ideal for capturing user credentials.

Question 20

How to prompt user for input and silently read it using read?

Answer 20

#!/bin/bash
# Prompt the user for credentials
read -p 'Username: ' username
read -sp 'Password: ' password
echo "Thanks, your creds are as follows: " $username " and " $password

Question 21

What is ‘#!’ in bash?

Answer 21

Shebang

Question 22

What is ‘/bin/bash’ in Bash scripting file?

Answer 22

Absolute path.

Question 23

What char is used to create comments in bash scripting?

Answer 23

#

Question 24

How to print string “Hello World!” to terminal?

Answer 24

echo “Hello World!”

Question 25

How to make script executable?

Answer 25

chmod +x

Question 26

How to run script “hello-world.sh”?

Answer 26

./hello-world.sh

Question 27

General syntax for the if statement in bash scripting?

Answer 27

if [ some test ]
then
perform an action
fi

Question 28

How to use the if statement in Bash to check age, and decline if age is less than 16?

Answer 28

#!/bin/bash
# if statement example
read -p "What is your age: " age
if [ $age -lt 16 ]
then
echo "DECLINE"
fi

Question 29

What is option ‘-lt’ in bash scripting?

Answer 29

Less than.

Question 30

Describe operator !EXPRESSION

Answer 30

The EXPRESSION is false

Question 31

Describe operator -n STRING

Answer 31

STRING length is greater than zero

Question 32

Describe operator -z STRING

Answer 32

The length of STRING is zero (empty)

Question 33

Describe operator STRING1 != STRING2

Answer 33

STRING1 is not equal to STRING2

Question 34

Describe operator STRING1 = STRING2

Answer 34

STRING1 is equal to STRING2

Question 35

Describe operator INTEGER1 -eq INTEGER2

Answer 35

INTEGER1 is equal to INTEGER2

Question 36

Describe operator INTEGER1 -ne INTEGER2

Answer 36

INTEGER1 is not equal to INTEGER2

Question 37

Describe operator INTEGER1 -gt INTEGER2

Answer 37

INTEGER1 is greater than INTEGER2

Question 38

Describe operator INTEGER1 -lt INTEGER2

Answer 38

INTEGER1 is less than INTEGER2

Question 39

Describe operator INTEGER1 -ge INTEGER2

Answer 39

INTEGER1 is greater than or equal to INTEGER2

Question 40

Describe operator INTEGER1 -le INTEGER2

Answer 40

INTEGER1 is less than or equal to INTEGER2

Question 41

Describe operator -d FILE

Answer 41

FILE exists and is a directory

Question 42

Describe operator -e FILE

Answer 42

FILE exists

Question 43

Describe operator -r FILE

Answer 43

FILE exists and has read permission

Question 44

Describe operator -s FILE

Answer 44

FILE exists and it is not empty

Question 45

Describe operator -w FILE

Answer 45

FILE exists and has write permission

Question 46

Describe operator -x FILE

Answer 46

FILE exists and has execute permission

Question 47

Describe operator -x FILE

Answer 47

FILE exists and has execute permission

Question 48

Using the test command in an if statement, check age and decline if it’s less than 16.

Answer 48

#!/bin/bash
# if statement example 2
read -p "What is your age: " age
if test $age -lt 16
then
echo "You might need parental permission to take this course!"
fi

Question 49

What is general syntax for the else statement?

Answer 49

if [ ]
then

else

fi

Question 50

Using the else statement in Bash check if age is less than 16, if it is, then DECLINE, if it isn’t then APPROVE.

Answer 50

#!/bin/bash
# else statement example
read -p "What is your age: " age
if [ $age -lt 16 ]
then
echo "DECLINE"
else
echo "APPROVE"
fi

Question 51

What is the elif syntax in bash?

Answer 51

if [ ]
then

elif [ ]
then

else

fi

Question 52

How to use elif statement in bash to read from user his age, if it’s less than 16 - DECLINE, if it’s above 16 - APPROVE, else if it’s greater than 60 - RESPECT.

Answer 52

#!/bin/bash
read -p "What is your age: " age
if [ $age -lt 16 ]
then
echo "DECLINE"
elif [ $age -gt 60 ]
then
echo "RESPECT"
else
echo "APPROVE"
fi

Question 53

Boolean logical operator AND in Bash?

Answer 53

&&

Question 54

Boolean logical operator OR in Bash?

Answer 54

||

Question 55

How to use the AND (&&) boolean operator, to check if user2 variable which you have declared as “kacper” is present in /etc/passwd file.

Answer 55

kacper@hopper:~$ user2=kacper
kacper@hopper:~$ user3=bob
kacper@hopper:~$ grep $user2 /etc/passwd && echo “$user2 found!”
kacper:x:1000:1000:,,,:/home/kacper:/bin/bash
kacper found!
kacper@hopper:~$ grep $user3 /etc/passwd && echo “$user3 found!” || echo “$user3 not found!”
bob not found!

Question 56

What 2 types of loops do we have in bash?

Answer 56

for and while

Question 57

What loops are designed for?

Answer 57

Loops help us with repetitive tasks that we need to run until a certain criteria is met.

Question 58

General syntax of the for loop?

Answer 58

for var-name in
do

done

Question 59

How to print 10.11.1.1 - 10.11.1.10 ip addresses using for loops in bash?

Answer 59

kali@kali:~$ for ip in $(seq 1 10); do echo 10.11.1.$ip; done
or
kali@kali:~$ for i in {1..10}; do echo 10.11.1.$i;done

Question 60

How to use brace expansion using ranges in Bash to print IP addresses in 10.11.1.1-10 range?

Answer 60

kali@kali:~$ for i in {1..10}; do echo 10.11.1.$i;done

Question 61

General syntax of the while loop

Answer 61

while [ ]
do

done

Question 62

How to use while loop bash to print IP addresses in range 10.11.1.1-10?

Answer 62

#!/bin/bash
# while loop example
counter=1
while [ $counter -le 10 ]
do
echo "10.11.1.$counter"
((counter++))
done

Question 63

How to write function in bash scripting?

Answer 63

function function_name {
commands...
}

OR

function_name () {
commands…
}

Question 64

How to use bash function to print a message to the screen?

Answer 64

#!/bin/bash
print_me () {
echo "You have been printed!"
}
print_me

Question 65

How to pass an argument to function in Bash?

Answer 65

#!/bin/bash
# passing arguments to functions
pass_arg() {
echo "Today's random number is: $1"
}
pass_arg $RANDOM

Question 66

How to return a value from Bash Function in this case?

return_me() {
echo “Oh hello there, I’m returning a random value!”
return $RANDOM
}

Answer 66

#!/bin/bash
# function return value example
return_me() {
echo "Oh hello there, I'm returning a random value!"
return $RANDOM
}
return_me
echo "The previous function returned a value of $?"

Question 67

How to declare a local variable “name” with value “kacper” using Bash Scripting?

Answer 67

local name=”kacper”

Question 68

What is the output?

#!/bin/bash
# var scope example
name1="John"
name2="Jason"
name_change() {
local name1="Edward"
echo "Inside of this function, name1 is $name1 and name2 is $name2"
name2="Lucas"
}
echo "Before the function call, name1 is $name1 and name2 is $name2"
name_change
echo "After the function call, name1 is $name1 and name2 is $name2"

Answer 68

kali@kali:~$ ./varscope.sh
Before the function call, name1 is John and name2 is Jason
Inside of this function, name1 is Edward and name2 is Jason
After the function call, name1 is John and name2 is Lucas

Question 69

How to download the index.html page from megacorpone.com?

Answer 69

kali@kali:~$ wget www.megacorpone.com

Question 70

How to indetify hyperlinks in the index.html file?

Answer 70

kali@kali:~$ grep “href=” index.html

Question 71

How to use grep to grab lines that contains “.megacorpone”, indicating the existence of a subdomain from index.html?

Answer 71

grep “href=” index.html | grep “.megacorpone”

Question 72

How to strip away lines that contains “www.megacorpone.com”?

Answer 72

grep -v “www.megacorpone.com”

Question 73

How to tell awk, we want second field?

Answer 73

‘{print $2}’

Question 74

What is ‘-F’ option in awk?

Answer 74

Multi-character delimiter

Question 75

How to use awk with a unique delimiter search? We want to get from file “index.html” all hyperlinks, that contains megacorpone domain, but isn’t the boring www.megacorpone.com address and also doesn’t have HTTP://

Answer 75

kali@kali:~$ grep “href=” index.html | grep “.megacorpone” | grep -v “www.megacorpone.com” | awk -F “http://” ‘{print $2}’

Question 76

How to use cut command to set the delimiter to “/”?

Answer 76

cut -d “/” -f 1

Question 77

How to cut domain name with cut?

Answer 77

cut -d “/” -f 1

Question 78

What is the most elegant solution with a regular expression to carve only .megacorpone.com from index.html file?

Answer 78

grep -o ‘[^/]*.megacorpone.com’ index.html | sort -u > list.txt

Question 79

How to check ip address of domain “facebook.com”?

Answer 79

host facebook.com