Command Line

Question 1

pwd

Answer 1

print working directory

It outputs the name of the directory you are currently in, called the working directory.

Question 2

cd

Answer 2

change directory

changes the working directory (when followed by an argument)

Question 3

What does ‘cd ..’ do?

Answer 3

moves up one directory

Question 4

ls

Answer 4

list all files and directories in the working directory

In addition to -a, the ls command has several more options. Here are three common options:

• a - lists all contents, including hidden files and directories
• l - lists all contents of a directory in long format
• t - order files and directories by the time they were last modified.

Question 5

mkdir

Answer 5

make a new directory

It takes in a directory name as an argument, and then creates a new directory in the current working directory.

Question 6

touch

Answer 6

Here we used touch to create a new file named keyboard.txt inside the 2014/dec/ directory.

Question 7

What is the ‘command line’?

Answer 7

The command line is a text interface for the computer’s operating system. To access the command line, we use the terminal.

Question 8

filesystem

Answer 8

A filesystem organizes a computer’s files and directories into a tree structure. It starts with the root directory. Each parent directory can contain more child directories and files.

Question 9

$

Answer 9

The shell prompt

Question 10

-a

Answer 10

The -a modifies the behavior of the ls command to also list the files and directories starting with a dot (.). Files started with a dot are hidden, and don’t appear when using ls alone.

The -a is called an option. Options modify the behavior of commands. Here we used ls -a to display the contents of the working directory in more detail.

Question 11

..

Answer 11

parent directory link

Question 12

.

Answer 12

current directory link

Question 13

What does -l list?

Answer 13

1) Access rights. These are actions that are permitted on a file or directory.
2) Number of hard links. This number counts the number of child directories and files. This number includes the parent directory link (..) and current directory link (.).
3) The username of the file’s owner. Here the username is cc.
4) The name of the group that owns the file. Here the group name is eng.
5) The size of the file in bytes.
6) The date & time that the file was last modified.
7) The name of the file or directory.

Question 14

-alt

Answer 14

The -t option orders files and directories by the time they were last modified.

In addition to using each option separately, like ls -a or ls -l, multiple options can be used together, like ls -alt.

Here, ls -alt lists all contents, including hidden files and directories, in long format, ordered by the date and time they were last modified.

Question 15

cp

Answer 15

The cp command copies files or directories.

Question 16

What command do you use to copy a file to a directory?

Answer 16

To copy a file into a directory, use cp with the source file as the first argument and the destination directory as the second argument.

Question 17

How do you copy multiple files into a directory?

Answer 17

To copy multiple files into a directory, use cp with a list of source files as the first arguments, and the destination directory as the last argument. (Here, we copy the files biopic/ray.txt and biopic/notorious.txt into the historical/ directory.)

Question 18

Copy all files in a directory

Answer 18

cp * directoryname/

Question 19

What does * do?

Answer 19

Selects groups of files. Specifically selects all files in the working directory.

Question 20

cp m*.txt scifi/

Answer 20

selects all files in the working directory starting with “m” and ending with “.txt” and copies them to scifi/

Question 21

mv

Answer 21

moves files. Similar to “cp” in its usage.

To move a file into a directory, use mv with the source file as the first argument and the destination directory as the second argument.

To rename a file, use mv with the old file as the first argument and the new file as the second argument.

Question 22

rm

Answer 22

The “rm” command deletes files and directories.

Question 23

rm -r

Answer 23

the “-r” is an option that modifies the behavior of the rm command. “-r” stands for recursive and it’s used to delete a directory and all of its child directories.

Question 24

echo

Answer 24

“echo” command accepts the strings as standard input and echoes the string back to the terminal as standard output.

Question 25

stdin

Answer 25

standard input. Information inputted into the terminal through the keyboard or input device.

Question 26

stdout

Answer 26

standard output. the information outputted after a process is run.

Question 27

stderr

Answer 27

standard error. error message outputted by a failed process.

Question 28

cat

Answer 28

the “cat” command outputs the contents of a file to the terminal.

Question 29

>

Answer 29

takes the standard output of the command on the left, and redirects it to the file on the right

Question 30

> >

Answer 30

takes the standard output of the command on the left and appends it to the file on the right. You can view the output data of the file with “cat” and the filename

Answer 31

takes the standard input from the file on the right and inputs it into the program on the left

Question 32

|

Answer 32

”|” is a pipe. the | takes the standard output of the command on the left and pipes it as standard input to the command on the right.

Think of this as “command to command” redirection.

Question 33

sort

Answer 33

“sort” takes the standard input and orders it alphabetically for the standard output.

Question 34

uniq

Answer 34

“uniq” stands for “unique” and filters out adjacent, duplicate lines ina file.

Question 35

grep

Answer 35

“grep” stands for “global regular expression print”. It searches files for lines that match a pattern and returns the results. NOTE: It is also case sensitive when enabled with -i like “grep -i “

Question 36

grep -R

Answer 36

searches all files in a directory and outputs filenames and lines containing matched results.

-R stands for “recursive”

Question 37

grep -Rl

Answer 37

searches all files in a directory and outputs only filenames with matched results.

-R stands for “recursive and “l” stands for “files with matches”

Question 38

sed

Answer 38

“sed” stand for “stream editor”. It accepts standard input and modifies it based on an expression before displaying it as output data.

NOTE: It is similar to “find and replace”

NOTE: “s” stands for substitution. It is always used when using sed for substitution.

Question 39

g

Answer 39

“g” expression, meaning “global”

$ sed ‘s/snow/rain/g’ forests.txt // sed searches forests.txt for the word “snow” and replaces it with “rain”, GLOBALLY.

Question 40

Each time we launch terminal, it creates…

Answer 40

a new session

Question 41

nano

Answer 41

opens the nano text editor

nano is a command line text editor. It works just like a desktop text editor like TextEdit or Notepad except it is accessible from the command line and only accepts keyboard input.

Question 42

Command to save the file (in nano editor)

Answer 42

Ctrl+O

Question 43

Command to exit nano

Answer 43

Ctrl+X

Question 44

Command to clear the terminal window

Answer 44

clear

Question 45

Name of the file used to store environment settings

Answer 45

the “bash profile”

i.e. $ nano ~/.bash_profile

When a sesion starts, it will load teh contents of the bash profile before executing commands.

Question 46

source

Answer 46

makes the changes available right away in the session we are in

Question 47

alias

Answer 47

The “alias” comnaomand allows you to create keyboard shortcuts, or aliases, for commonly used commands.

Question 48

alias hy=”history”

Answer 48

hy is set as alias for the “history” command in the bash profile. The alias is then made available in teh current session through “source”. By typing “hy”, the command line outputs a history of commands that were entered in the current session

Question 49

environment variables

Answer 49

environment variables are variables that can be used across commands and programs and hold information about the environment.

e.g. export USER=”Jane Doe”

Question 50

What command do you use to make a variable available to all child sessions initiated from the session you are in?

Answer 50

export

e.g. export USER=”Jane Doe”

Question 51

What is always used when returning a variable’s value?

Answer 51

$

Question 52

Define “PS1”

Answer 52

PS1 is a variable that defines the makeup and style of the command prompt.

Ex: export PS1=”» “ // sets the command prompt variable and exports the variable. After you use “source” command, the command line displays the new command prompt.

Question 53

Define “HOME”

Answer 53

The HOME variable is an environment variable that displays the path of the home directory.

NOTE: You can customize the HOME variable if needed, but in most cases this is not necessary.

Question 54

Define “PATH”

Answer 54

PATH is an environment variable that stores a list of directories separated by a colon.

Each directory contains scripts for the command line to execute. The PATH variable simply lists which directories contain scripts.

Question 55

env

Answer 55

The env command stands for “environment”, and returns a list of the environment variables for the current user.

Question 56

env | grep PATH

Answer 56

env | grep PATH is a command that displays the value of a single environment variable. Here the standard output of env is “piped” to the grep command. grep searches for the value of the variable PATH and outputs it to the terminal.