2. Codecademy: Learn the Command Line

Question 1

(Left angle bracket)

Answer 1

Redirect standard output to a command.

For some reason, the app is deleting the actual less than symbol, also referred to as the left angle bracket

Question 2

’ > ‘

Answer 2

Redirect standard output of a command to a file, overwriting its previous contents.

Question 3

’&raquo_space; ‘

Answer 3

Redirect standard output of a command, appending original contents of a file.

Question 4

’ | ‘

Answer 4

Pipe symbol; Redirect standard output of a command to another command.

Question 5

*

Answer 5

The asterisk acts as a wildcard to select files and directories.

(E.g., cp m*.txt Movies/ copies all .txt files stating with the letter ‘m’ into the Movies/ directory)

Question 6

wc

Answer 6

Output number of lines, words, and characters

Question 7

sort

Answer 7

Order the contents of the standard input alphabetically for the standard output.

Question 8

uniq

Answer 8

Filter out adjacent, duplicate lines in a file.

(best used in a pipeline with ‘sort’ e.g.,
$sort deserts.txt | uniq
which sorts the contents of desert.txt alphabetically, making duplicates adjacent and filtering them out of the output of the uniq command)

Question 9

-r or -R

Answer 9

Meaning “recursive,” when following a command it acts as an option

(See rm -r and grep -R)

Question 10

ls -a

Answer 10

List all files and directories in the working directory, including any hidden files (files starting with ‘ . ‘ are hidden by default)

Question 11

ls -l

Answer 11

List all files and directories in long format

Question 12

ls -t

Answer 12

List all files and directories by date last modified

Question 13

ls -alt

Answer 13

List all files and directories, including hidden files, in long format, by date last modified

(ls options can be combined in any combination, e.g., ls -al, ls -at, ls -lt)

Question 14

rm -r

Answer 14

Remove directory and all of its contents (permanently!!)

Question 15

-i

Answer 15

disregard case/case insensitive

Question 16

grep -R

Answer 16

Search all files in a directory and output file names and lines containing matched results.

Question 17

grep -Rl

Answer 17

Search all files in a directory and output only file names with matched results.

Question 18

sed

Answer 18

Stands for “stream editor.” Accepts, modifies, then prints standard input based on an expression containing other commands.

(See ‘s’ and ‘g’)

Question 19

s

Answer 19

sed expression meaning substitute ‘this string’ of the standard input for ‘that string’ in the standard output. (Only substitutes first instance of ‘this string’ unless ‘g’ expression is used).

(using the following syntax: sed s/this/that filename
e.g., sed s/snow/rain forests.txt)

Question 20

g

Answer 20

sed expression meaning global or search globally

e.g., $sed s/snow/rain/g forests.txt

Question 21

Redirection

Answer 21

Reroutes standard input, standard output and standard error

using commands including >, >, |, etc

Question 22

nano

Answer 22

a command line text editor

Type nano followed by the filename you would like to open; if filename does not exist a new file will be created

Question 23

~

Answer 23

The tilde symbol represents the user’s home directory.

Question 24

.

Answer 24

Files starting with ‘ . ‘ are hidden files.

Question 25

USER

Answer 25

Environment variable that denotes computer owner’s name or current user

Question 26

PS1

Answer 26

Environment variable that defines the makeup and style of the command prompt

(default ends with $)

Question 27

PATH

Answer 27

Environment variable that lists which directories contain scripts.

Question 28

du

Answer 28

print the disk usage of a directory

Question 29

du -h

Answer 29

print list of sizes of subdirectories in a directory in ‘human readable format’

Question 30

du -sh

Answer 30

print the total size of directory in ‘HRF’

Question 31

du - a

Answer 31

du -a print list of the sizes of all files/directories

Question 32

du -ah

Answer 32

print list of sizes of all files/directories in HRF

Question 33

Ctrl + a

Answer 33

Move cursor to front of line

Question 34

Ctrl + e

Answer 34

Move cursor to end of line

Question 35

Ctrl + u

Answer 35

Clear current line

Question 36

Ctrl + l

Answer 36

Clear terminal window (not history)

Question 37

Toggle previous commands

Answer 37

Up and Down arrow keys