Command Line

Question 1

What is $echo ?

Answer 1

It repeats the argument you type in with a new trailing newline character

Question 2

What does the flag in $echo -n mean?

Answer 2

No new trailing newline character for the echo command

e.g. $echo Hello World
=> Hello World
=> $
e.g. $echo -n Hello World
=>Hello World $

Question 3

Does $echo “Hello World” -n works to eliminate new trailing newline character?

Answer 3

No. Flag always comes before arguments.

Question 4

What does it mean:

$cd /

Answer 4

Change directory to ROOT directory.

NOTE: there’s a space in front of “/”

Question 5

How to go back to your home directory in CLI?

Answer 5

$cd ~

Question 6

What does it mean:

$pwd

Answer 6

It shows you your current directory is at.

pwd = Print Working Directory

Question 7

What does it mean:

$ls

Answer 7

It shows you the files and directory under your current directory

ls = LiSt directory

Question 8

What does it mean:

$ mkdir This is good

Answer 8

It creates a new directory under the directory you’re at
** You should name the new directory in the arguments

mkdir = Make Directory

Question 9

What does it mean:

$touch abc.txt

Answer 9

This command creates a new file (*not directory) in the current directory

** type the file name and its file type in the arguments

abc.txt = a text file named “abc”

Question 10

How to rename a file (named “toy.txt”)?

Answer 10

$ mv toy.txt toy2.txt

Question 11

How does the pattern of $ mv works?

Answer 11

$ mv [source] [destination]

1) if you want to change the file name, determine the source file name and write the new name in destination.
2) if you want to move a file to another directory - specify you source file name and write the destined directory in the destination (**it does not apply to move from a subdirectory back to parent directory, see point 3) (file directory needs to have slash behind file name, e.g. tmp/)

3) You can even take a file in a directory under your current directory back to your current directory; and then rename it (if you only move and no rename, still need to type in the original name).
e.g. $ mv tmp/example1.txt example2.txt
$ mv tmp/example1.txt example1.txt

Question 12

How to go back to the parent directory?

Answer 12

$ cd ..

.. = two dots

Question 13

How to remove a file (e.g. “abc.txt”)?

Answer 13

$ rm abc.txt

Question 14

How to remove a directory (e.g. “Tealeaf”)

Answer 14

$ rm -r Tealeaf

*Remember to add the flag -r for recursive delete of a directory; it’s different from just deleting a file.

Question 15

How to exit from content listing command like $ man or $ less ?

Answer 15

type q

Question 16

What does $ cat do?

Answer 16

It prints out all contents of a file

see also: $ head / $ tail / $ more / $ less

Question 17

What does $ head do?

Answer 17

It prints out the first few lines of a file

see also: $ cat / $ tail / $ more / $ less

Question 18

What does $ tail do?

Answer 18

It prints out the last few lines of a file

see also: $ more / $ cat / $ head / $ less

Question 19

What does $ more do?

Answer 19

It prints out the content of a file but only fills one screen worth at a time

Question 20

In Linux/Unix CLI, what does “/” mean?

Answer 20

1) Root directory

2) Separator when listing directories

Question 21

In Linux/Unix CLI, what does “.” mean?

Answer 21

The current directory

=> also as “./”

Question 22

In Linux/Unix CLI, what does “..” mean?

Answer 22

The directory one level up

=> also as”../”

Question 23

In Linux/Unix CLI, what does “../..” mean?

Answer 23

The directory two levels up

Question 24

In Linux/Unix CLI, what does ~ mean?

Answer 24

Home diretory

Question 25

In Linux/Unix CLI, what does “*” mean?

Answer 25

The splat/ glob operator.
=> represents “any characters”

e.g. ls /*e
list all files (not directories) that ends with “e”

e.g.2 mv ./* ../
=> move all files in current directory to parent directory

Question 26

How to create a nested set of directories in your home directory: cli-tmp > parents > children > grandchildren

Answer 26

mkdir -p ~/cli-tmp/parents/children/grandchildren

Question 27

Which one represents one directory up?

/..
../

Answer 27

../

Question 28

How to copy a directory with files (e.g. phone) and change the name (e.g. eight) at once?

Answer 28

$ cp -r phone eight

Question 29

How to list all files, including hidden ones

Answer 29

$ ls -a

All hidden files are named with a dot as first letter.
Hence, hidden files are also named dotfiles

Question 30

How to list hidden only files?

Answer 30

$ls -d .*

.* => all dotfiles / hidden files

Question 31

How to set environment Variables on the fly?

2 methods: set and then execute everywhere; set for a specific command at the same line

Answer 31

1)
$ CALIFORNIA=’CA’
$ echo $CALIFORNIA

2)
$ CALIFORNIA=’CA’ env
this method only sets variable to $env

*quote the value of variable, especially if there is special character in the value.

**no space between equal sign and value

Question 32

What will it do: $ top

Answer 32

It shows your computer working environment like CPU usage, programs you are using, etc.