Intro to Command Line

Question 1

Difference between /home/ubuntu and home/ubuntu

Answer 1

/home/ubuntu This path specifies a folder called “ubuntu” that lives under your root directory, then home directory.

home/ubuntu This path specifies a completely different folder. This path means there’s a folder called “ubuntu” that lives in a directory called “home”, which is itself in the current directory.

Question 2

difference between ls and ls/

Answer 2

ls just shows list of current directory. ls/ shows list of root directory

Question 3

Display contents of a file in an interactive way

Answer 3

less

Question 4

Display documentation about a command

Answer 4

man

Question 5

Display last part of a file

Answer 5

tail

Question 6

How do display contents of a file?

Answer 6

cat

Question 7

How do you create a file in the CLI?

Answer 7

touch

Question 8

How to copy a file in CLI

Answer 8

cp

Question 9

How to Display contents of a file, starting at the top and letting the user scroll down?

Answer 9

more

Question 10

How to display first part of a file

Answer 10

head

Question 11

How would you list any files or folders that end in ‘ot’?

Answer 11

ls /*ot

Question 12

What does the ~ symbol mean?

Answer 12

~ - Your “home” directory, or the directory you are placed in when you log in.

Question 13

What makes an executable different from other files?

3 reasons

Answer 13

1. They have special characters at the beginning to tell the computer how to execute them.
2. They have scripts or machine language as their content.
3. They have the executable permission

Question 14

How to list hidden files (dotfiles) in the current directory?

Answer 14

ls -a ~

Question 15

What’s the difference between abc/ and /abc?

Answer 15

The path abc/ (also ./abc and ./abc/) are paths relative to your current working directory. The path /abc, however, is the file or directory abc in the root directory.

Question 16

How To figure out a default executable’s location?

Answer 16

which

Question 17

How to re-initialize a particular environment file (such as .bashrc)

Answer 17

source ~/.bashrc

Question 18

To have a variable get interpolated, do you use single or double quotation marks?

Answer 18

Double quotation marks.

Example:

 $ MESSAGE1="This is message 1."
$ MESSAGE2="This is message 2."
$ MESSAGE="$MESSAGE1 $MESSAGE2"
$ echo $MESSAGE
This is message 1. This is message 2.

Question 19

What does the PATH variable do?

Answer 19

The PATH variable determines which directories are searched when a command is entered

You can add to PATH to make more commands available without having to memorize their exact path

Modifications to PATH, or any environment variable, on the fly will not be permanent; permanent modifications should be done in an environment file, like .bashrc

Question 20

What does&raquo_space; do?

Answer 20

The redirection operator (») is used to append text to a file. If the target file doesn’t exist, then it will be created.

Question 21

But why use sudo instead of just logging in as root? leave your Terminal open on accident.

Answer 21

There are several reasons for doing this, including the following:

The server administrator wants you to have root access for some commands and/or directories, but not for everything. In this case the administrator will set up sudo to have restrictions or whitelisted commands.

Running commands while logged in as root can be dangerous. Using a non-root user makes it obvious when you are running a command that requires root privileges because you have to prefix your command with sudo.

The sudo command provides a detailed audit trail so that system administrators can track what commands individuals used on system files.

Sudo uses a ticketing system where you put in your password once, then you don’t have to until you haven’t run any sudo commands for five minutes or longer. This adds security to your command line session, preventing others from gaining root access if you

Question 22

What does a REPL stand for?

Answer 22

Interfaces that Read Input, Evaluate Input, Print results and Loop back

Question 23

What are some examples of REPL interfaces?

Answer 23

mysql, ruby, python, or editors like vim and nano