Shell

Question 1

Which command lets you find out where you are in the filesystem?

Answer 1

pwd

Question 2

Which command lets you list the content of your directory?

Answer 2

ls

Question 3

Which command lets you list the content of a specific directory?

Answer 3

ls /path/to/file

Question 4

What is the conceptual difference between asbolute and relative paths?

Answer 4

An absolute path is like a latitude and longitude: it has the same value no matter where you are.

A relative path, specifies a location starting from where you are: it’s like saying “20 kilometers north”.

Question 5

How does the shell decide if a path is relative or absolute?

Answer 5

An absolute path starts with a /.

A relative path doesn’t.

Question 6

Which command lets you move around the filesystem?

Answer 6

cd

Question 7

What is the parent of a directory?

Answer 7

The parent of a directory is the directory above it. For example, /home is the parent of /home/repl, and /home/repl is the parent of /home/repl/seasonal.

Question 8

Which special path corresponds to the one above the one you’re currently in?

Answer 8

..

Question 9

Which path is the root directory?

Answer 9

/

Question 10

Which path corresponds to the current directory?

Answer 10

.

Question 11

Which path corresponds to the home directory?

Answer 11

~

Question 12

Which command lets you copy files?

Answer 12

cp path/original.txt path/duplicate.txt

Question 13

How do you copy several files to a directory?

Answer 13

cp original1.txt original2.txt path/to/directory

Question 14

Which command lets you move files from on directory to another?

Answer 14

mv path/to/file1.txt path/to/file2.txt path/to/directory

Question 15

Which command lets you rename a file?

Answer 15

mv old_name.txt new_name.txt

Question 16

Which command lets you remove files?

Answer 16

rm file/to/file1.txt file/to/file2.txt

Question 17

What happens if you move or copy to an existing filename?

Answer 17

The original file with that filename is overwritten.

Question 18

Which command lets you remove an empty directory?

Answer 18

rmdir directory_name

Question 19

Which command lets you create a directory?

Answer 19

mkdir directory_name

Question 20

Where should you store files and programs you only need briefly?

Answer 20

/temp

Question 21

Which command lets you look at the content of files?

Answer 21

cat file1.txt file2.txt

Question 22

When printing the content of a file, how do you go to the next page?

Answer 22

Press the spacebar

Question 23

When printing the content of a file, how do you quit?

Answer 23

Press q

Question 24

When printing the content of several files, how do you move to the next file?

Answer 24

Type :n

Question 25

When printing the content of several files, how do you move to the previous file?

Answer 25

Type :p

Question 26

When printing the content of several files, how do you quit?

Answer 26

Type :q

Question 27

Which command lets you print the first 10 lines of a csv file?

Answer 27

head file.csv

Question 28

What are command-line flags?

Answer 28

They are a way to specify options for command-line programs. For example, head -n 5 file.csv specifies head should print 5 lines instead of the default 10.

Question 29

By convention, where should command-line flags be placed?

Answer 29

By convention, command-line flags should be placed before any filenames.

Question 30

How do you display everything that is underneath directory?

Answer 30

ls -R

Question 31

When listing files, how do you make it clear which ones are directory names and which ones are runnable programs?

Answer 31

ls -F

Question 32

Which command lets you obtain documentation on a specific command?

Answer 32

man command

Question 33

Which command lets you display columns?

Answer 33

cut

Question 34

When selecting columns, which flag lets you specify the column delimiter?

Answer 34

-d , | (for columns separated by commas)

Question 35

When selecting columns, which flag lets you specify the columns or range of columns to select?

Answer 35

-f 1-4 7 | (columns 1 to 4 and 7)

Question 36

When displaying the content of a file, how do you skip the first x lines?

Answer 36

-n +x

Question 37

Which command lets you display a list of commands you have run recently?

Answer 37

history

Question 38

How do you rerun your most recent use of a command?

Answer 38

!command

Question 39

How do you rerun the xth command in your history?

Answer 39

!x

Question 40

How do you display lines of files containing a specific piece of text?

Answer 40

grep keyword path/to/file

Question 41

With grep, which flag lets you print a count of matching lines rather than the lines themselves?

Answer 41

grep -c

Question 42

With grep, which flag lets you not print the names of the files when searching multiple files?

Answer 42

grep -h

Question 43

With grep, which flag lets you ignore case?

Answer 43

grep -i

Question 44

With grep, which flag lets you print the names of the files that contain the matches, rather than the matches themselves?

Answer 44

grep -l

Question 45

With grep, which flag lets you print only lines that don't match?

Answer 45

grep -v

Question 46

Which command lets you combine files?

Answer 46

paste file1.csv file2.csv

Question 47

How do you save a command's output?

Answer 47

Use redirection: tail -n 5 file.csv \> last5.csv

Question 48

Which command lets you print the number of characters, words, and lines in a file?

Answer 48

wc

Question 49

Which wc flag lets you print the number of characters only?

Answer 49

wc -c

Question 50

Which wc flag lets you print the number of words only?

Answer 50

wc -w

Question 51

Which wc flag lets you print the number of lines only?

Answer 51

wc -l

Question 52

What is a wildcard and why are they useful?

Answer 52

A wildcard is a character that can be used as a substitute for any of a class of characters in a search, thereby greatly increasing the flexibility and efficiency of searches.

Question 53

Which wildcard matches 0 or more characters?

Answer 53

\*

Question 54

Which wildcard matches a single character?

Answer 54

?

Question 55

Which wildcard matches any one of the characters passed?

Answer 55

[characters]

Question 56

Which wildcard matches any of the comma-separated patterns passed?

Answer 56

{pattern1, pattern2}

Question 57

Which command lets you order values?

Answer 57

sort

Question 58

Which sort flag lets you sort in numerical order instead of the default alphabetical order?

Answer 58

-n

Question 59

Which sort flag lets you sort in descending order instead of the default ascending order?

Answer 59

-r

Question 60

Which sort flag lets you ignore leading blanks?

Answer 60

-b

Question 61

Which sort flag lets you fold case (be case-insensitive)?

Answer 61

-f

Question 62

Which command lets you remove adjacent duplicated lines?

Answer 62

uniq

Question 63

Which uniq flag lets you display the count of duplicated lines?

Answer 63

-c

Question 64

In a command expression, where should the command writing to a file appear?

Answer 64

At the very beginning or at the very end.

Question 65

How do you interrupt a runing command?

Answer 65

Ctrl + C

Question 66

Which environment variable corresponds to the user's home directory?

Answer 66

HOME

Question 67

Which path corresponds to HOME?

Answer 67

/home/repl

Question 68

Which environment variable corresponds to the present working directory?

Answer 68

PWD

Question 69

Which environment variable corresponds to the shell program being used?

Answer 69

SHELL

Question 70

Which path corresponds to SHELL?

Answer 70

/bin/bash

Question 71

Which environement variable corresponds to the user's ID?

Answer 71

USER

Question 72

Which command lets you print the value of an environment variable?

Answer 72

printenv ENVIRONMENT\_VARIABLE or echo $ENVIRONMENT\_VARIABLE

Question 73

Which command lets you display a list of all environment variables?

Answer 73

set

Question 74

How do you create a shell variable?

Answer 74

variable=value without spaces before or after =

Question 75

How do you print the value of a variable?

Answer 75

echo $variable

Question 76

How do you define a for loop?

Answer 76

for *variable* in *list* **;** do *command* **;** done

Question 77

How do you indicate a variable name instead of the name you have typed.

Answer 77

$ (use a dollar in front of the variable, eg echo $variable)

Question 78

If you have filenames with spaces, how do you work around that so your command interprets filenames correctly?

Answer 78

Wrap filenames in single or double quotes ('' or "").

Question 79

How do you separate several commands in the body of a for loop?

Answer 79

;

Question 80

How do you open a file with nano?

Answer 80

nano filename

Question 81

How do you delete a line with nano?

Answer 81

Ctrl + K

Question 82

How do you undelete a line with nano?

Answer 82

Ctrl + U

Question 83

How do you save the file with nano?

Answer 83

Ctrl + O

Question 84

How do you exit the editor with nano?

Answer 84

Ctrl + X

Question 85

How do you create a file with nano?

Answer 85

nano filename

Question 86

How do you store commands so you can reuse them later?

Answer 86

Write commands to a .sh file. Although scripts don't have to have names ending in .sh, it's good practice as it helps keep track of which files are scripts.

Question 87

Which command lets you execute commands contained in a .sh file?

Answer 87

bash name.sh

Question 88

How do you call a file full of shell commands?

Answer 88

A shell script.

Question 89

How do you provide a placeholder to a command in a script?

Answer 89

$@

Question 90

How do you execute a shell script with a placeholder?

Answer 90

bash file.sh placeholder

Question 91

How do you provide several placeholders to a shell script?

Answer 91

Use $1, $2...

Question 92

How are several placeholders passed to a shell script?

Answer 92

In the order in which they appear in the bash command calling the script. You need to pay extra attention to the order of the placeholders in the script and in your commands call, to ensure you're passing the appropriate value at the appropriate placeholder.

Question 93

How do you write loops in scripts?

Answer 93

Use semi-colons, or declare them on several lines without semi colon following this format: ## Footnote for value in variable do command1 command2 done Commands do not have to be indented, but doing so makes things clearer.

Question 94

How do you add comments to a script?

Answer 94

Use # at the beginning of the line.