Bash Scripting

Question 1

what is relative path?

Answer 1

location from the current directory

Question 2

what’s absolute path?

Answer 2

something like /bin/ping

-used in case the program is not specified in PATH

Question 3

~

Answer 3

current user’s home directory

Question 4

*

Answer 4

wildcard used for finding certain types of files

Question 5

output

Answer 5

results of command in a bash shell

Question 6

command > file.txt

Answer 6

create or overwrite

Question 7

command»_space; file.txt

Answer 7

create or append

Question 8

what are 2 types of output redirection

Answer 8

1. to a file

2. to another command

Question 9

what bash character sends output to another command?

Answer 9

(pipe)

Question 10

what is a “oneliner” script?

Answer 10

chaining multiple commands to automate a task

Question 11

what does this oneliner do?

file ‘ls /etc/*conf’ | sort > test.txt && cat test.txt | wc -l

Answer 11

1. anything between ‘’ operator gets evaluated first
2. for each file listed (ls), it is sorted and put into a text file called test.txt
3. && means execute what’s after it if the previous commands were successful
4. read the test.txt file and print out the number of lines (wc = word count -l = lines)

Question 12

what extension does a bash script file have?

Answer 12

.sh

Question 13

what is the first line of any bash script file?

Answer 13

!/bin/bash

Question 14

after saving a bash file, what should you make sure of?

Answer 14

make sure the file is executable, change the permissions

Question 15

how do you make a file executable?

Answer 15

chmod+x

Question 16

how do you run a script in linux terminal?

Answer 16

./

Question 17

what is they syntax for a bash conditional statement?

Answer 17

if ; then
commands
elif ; then
commands
else
commands
fi

Question 18

What do these operators mean?

• eq
• ne

Answer 18

equal

not equal

Question 19

What do these operators mean?

• lt
• le

Answer 19

less than

less than or equal to

Question 20

What do these operators mean?

• gt
• ge

Answer 20

greater than

greater than or equal to

Question 21

what does this for loop do?
#!/bin/bash

for i in $( ls ); do
echo item: $i
done

Answer 21

print out every item in a current directory

Question 22

what does this for loop do?
#!/bin/bash

for i in ‘seq 1 10’;
do
echo $i
done

Answer 22

uses the ‘seq’ command to iterate over numbers

Question 23

what is the ‘while’ loops useful for

Answer 23

iterating over items in a file

Question 24

what does the script below do?

while[condition]; do ; ; done

Answer 24

basic syntax to iterate over times

Question 25

what does the script below do? while read line; do echo $line; done < file.txt

Answer 25

read and print items from a file

Question 26

what does grep do?

Answer 26

filter for the chosen keyword

Question 27

what does the following do? cat *.nmap | grep "open" cat *.nmap | grep "open" | grep -v "filtered" cat *.nmap | grep "open" | grep -v "filtered" | cut -d "/" -f 1 cat *.nmap | grep "open" | grep -v "filtered" | cut -d "/" -f 1 | sort -u cat *.nmap | grep "open" | grep -v "filtered" | cut -d "/" -f 1 | sort -u | xargs cat *.nmap | grep "open" | grep -v "filtered" | cut -d "/" -f 1 | sort -u | xargs | tr ' ' ',' cat *.nmap | grep "open" | grep -v "filtered" | cut -d "/" -f 1 | sort -u | xargs | tr ' ' ',' > ports.txt

Answer 27

1. output a list of open ports 2. remove the item with the word "filtered" 3. print out only port numbers 4. sort/remove duplicates, keep only unique 5. put side by side 6. save to file ports.txt -d is a marker -f specifies which element should be printed after splitting 1 is the first element -u is unique tr translate or delete characters (tr ,text2replace, replacement)

Question 28

what command issues http requests to see their responses

Answer 28

curl aka command-line browser

Question 29

where is the linux "black hole" where all sent items are deleted

Answer 29

/dev/null

Question 30

what is one way you can use curl if you have a list of domains/IP?

Answer 30

you can use it to test domains/IP to see if they are an http or and https server

Question 31

in an instance of curl, what flag allows you to format it's output?

Answer 31

--write-out

Question 32

what does the following do? curl --write-out "%{http_code}" http://google.com curl --write-out "%{http_code}\n" --output /dev/null --silent http://google.com

Answer 32

1. outputs http response from website and it's response code 2. removes unnecessary/unreadable output, \n adds new line, --silent removes errors 3.

Question 33

what does the flag -L do for curl?

Answer 33

follow redirections

Question 34

what does the flag --insecure do for curl?

Answer 34

bypass bad ssl error code

Question 35

what does the following do? timeout 5 curl -L --write-out "%{http_code}\n" --output /dev/null --silent --insecure http://google.com

Answer 35

1. if response is taking too long it times out after 5 seconds 2. follows redirect if any 3. only returns response code and sends other output to black hole 4. --silent doesn't return any errors 5. --insecure bypasses bad or no ssl