Lesson 3

Question 1

How does compression work?

Answer 1

By replacing repetitive patterns in data. For example finding a common word and replacing it with something else then creating a map to that replacement (obv more complex)

Question 2

What are the two types of compression?

Answer 2

Lossless and Lossy

Question 3

When is lossy compression often used?

Answer 3

For images, video or audio where loss in the original data has a marginal effect

Question 4

Name some common lossless compression tools

Answer 4

bzip2, gzip, xz

Question 5

What is the most common archiving tool?

Answer 5

tar

Question 6

how do you uncompress? name the common commands

Answer 6

bunzip2, gunzip, unxz

Question 7

How can you increase or decrease the level of compression?

Answer 7

By using -1 through -9…common among all compression tools

Question 8

what is the syntax for a tar command to compress?

Answer 8

tar -cf newfile pathtoarchive

Question 9

what is the syntax to untar?

Answer 9

tar -xf <file/path>

Question 10

When using tar with gzip, bgzip2 and xz what are the commands?

Answer 10

gzip = tar -xzf
bzip2 = tar -xjf
xz = tar -xJf

Question 11

syntax to zip recursively

Answer 11

zip -r filename filepath

Question 12

syntax to unzip

Answer 12

unzip filename

Question 13

how to output the contents of a compressed file?

Answer 13

zcat gzip, bzcat for bzip2

Question 14

how do add a file to a compressed tar?

Answer 14

First you need to uncompress it so gunzip or bunzip2 or unxz…then use tar uf to add a new file

Question 15

how to view contents of a tar without extracting it?

Answer 15

tar -tf filename

Question 16

Which tar option instructs tar to include the leading “/” in the absolute paths?

Answer 16

-P

Question 17

Does zip support multiple compression levels?

Answer 17

Yes same as the other compression tools

Question 18

When extracting and archive, does tar support wildcards?

Answer 18

Yes with the –wildcards option

Question 19

How can you ensure decompressed files are lossless?

Answer 19

bzip2, gzip, and xz all have checksums built in to ensure this

Question 20

What is I/O redirection?

Answer 20

Enabled you to redirect information from or to a command by using a text file

Question 21

Which character to redirect std out to a file?

Answer 21

> for example echo "hello world" > text

Question 22

Which characters to redirect std out but add to a file?

Answer 22

>>

Question 23

Which characters to redirect errors to a file?

Answer 23

2>

Question 24

How to redirect standard input to a command?

Answer 24

< example:
cat < text

Question 25

what does &> and &» do?

Answer 25

They redirect BOTH std out and errors to the file, &» just appends to it

Question 26

explain how the cut command works

Answer 26

First you give it the column with -f <number> and then a delimiter to make columns on with -d</number>

Question 27

what does -f do with the tail command?

Answer 27

Lives updates the file as you have it open so you can follow logs, etc

Question 28

with tail and head how can you specify the number of lines to show?

Answer 28

-n <number>

Question 29

with sort command how can you reverse the sort?

Answer 29

-r command

Question 30

Using grep, how can you search a file for certain string?

Answer 30

grep word filename

Question 31

name some common grep options

Answer 31

-i = case insensitive
-r = recursive
-c = includes count of matches
-v = invert the match
-E = used for regex (needed for *, +, ?)

Question 32

Using regex with grep, what are the starting and end marking characters?

Answer 32

start = ^
end = $

Question 33

Grep syntax for “OR”

Answer 33

grep -E "foo|bar" filename

Question 34

what does the question mark operator do?

Answer 34

it makes the preceding pattern optional (zero or one)

Question 35

What does it mean to define the interpreter?

Answer 35

use which bash to determine the type of interpreter you want to use as the shebang

Question 36

in bash, how can I assign a variable to an input from the command line?

Answer 36

foo=$1

applies from 1-9

Question 37

How to get the number of arguments passed into a bash script?

Answer 37

$#

Question 38

what does bash if then syntax look like?

Answer 38

```base
if [ condition ]
then
…
else
…
fi
~~~

Question 39

List common bash comparison operators

Answer 39

```bash
-eq
-ne
-gt
-ge
-lt
-le
~~~

Question 40

how to get the exit code of the previously run command?

Answer 40

echo $?

Question 41

What does the wildcard character $@ or $*

Answer 41

Contains all arguments passed to the script in an array

Question 42

with echo how can you suppress new lines?

Answer 42

-n

Question 43

what does “shift” do in bash?

Answer 43

Removes the first element of an array