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&raquo_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