week 7

Question 1

Brace Expansions

Answer 1

Bash can fill in a pattern contained in braces
I.E echo {1 .. 10 .. 2}

Question 2

command substitution

Answer 2

allows you to store the output of a command in a variable
ie list = $(ls)

Question 3

arithmetic expansion

Answer 3

Evaluates a mathematical expression inside
ie $(( arithmetic ))

Question 4

pattern matching: *

Answer 4

matches any sequence of characters

Question 5

pattern matching: ?

Answer 5

matches any single character

Question 6

pattern matching: []

Answer 6

matches any enclosed characters

Question 7

Declaring function in Bash

Answer 7

function() {
body
}

Question 8

How do you pass a argument into a bash function?

Answer 8

you must use positional parameters ie $1

Question 9

Local variables

Answer 9

use the keyword ‘local’ behind what you want to be local scoped only
i.e. local users=$@

Question 10

How do you return a value in a bash function?

Answer 10

echo what you want to return and assign the return to a new variable

Question 11

Case

Answer 11

alternative to if/elif/else statements, allows you to patter match possible options and return something different depending
;; = end of condition
| = alternate condition
esac = end
i.e Case expression in:

A)
Echo A
;;
B)
echo B
;;
*)
echo everything
;;
esac

Question 12

OPTARG

Answer 12

OPTARG contains the arguments used for each flag and is generally used in conjunction with while and case

while getopts “:a:b:” opt; do
case “${opt}” in
a) example=${OPTARG}
esac
done

Question 13

shift

Answer 13

Shifts positional parameters n characters to the left, shift can stack with each other

Question 14

what is YAML?

Answer 14

“YAML ain’t markup language”, a human readable, data serialization language

Question 15

What command do you use to quit a process?

Answer 15

kill

Question 16

what signal is sent by default when using the “kill” command?

Answer 16

SIGTERM

Question 17

How do you send a different signal/SIGKILL with kill?

Answer 17

kill -9 or kill -SIGKILL

Question 18

How to show %mem with ps?

Answer 18

ps aux

option: add –sort=-%mem

Question 19

What is the signal code for sigint?

Answer 19

2

Question 20

what is the signal code for SIGKILL

Answer 20

9

Question 21

what is the signal code for SIGTERM

Answer 21

15

Question 22

How to find all lines that begin with a certain word? (regex)

Answer 22

grep “^GNU”

Question 23

how to find lines that end with a certain word? (regex)

Answer 23

grep “word$”

Question 24

What’s the difference between “.” and “?” in regex?

Answer 24

”?” matches for zero or more occurences while “.” matches any character

Question 25

How to add user to a group>

Answer 25

sudo usermod –aG groupname username

Question 25

How do you set password expiry?

Answer 25

sudo chage -M days username

Question 26

how to change ownership of a file?

Answer 26

sudo chown username:group filename

-R for recursive

Question 27

Where would you find a list of groups?

Answer 27

/etc/group

Question 28

command for creating a new group

Answer 28

groupadd

Question 29

Where is the config file for nvim located?

Answer 29

/home/user/.config/nvim/init.lua

Question 30

what does the shebang do?

Answer 30

tells the shell what interpreter to use

Question 31

how to make variable accessible in subshell?

Answer 31

export $var

Question 32

what would you use declare for?

Answer 32

1. creating an associative array (-A)
2. provide attributes to variables (-r for readme, NUM for int variable)

Question 33

how to check if a file is older than another one using conditionals in scripting?

Answer 33

-ot

Question 34

How to get all array items?

Answer 34

array[@]

Question 35

how to get number of items in an array?

Answer 35

array[@]

Question 36

what’s the difference between pkill and kill?

Answer 36

pkill allows you to kill a process vi