Chapter 3: Command Line Fun

Question 1

How do you view the PATH variable?

Answer 1

echo $PATH

Question 2

How do you view the USER variable?

Answer 2

echo $USER

Question 3

How do you view the HOME variable?

Answer 3

echo $HOME

Question 4

What is the export command?

Answer 4

The export command defines a variable.

Question 5

Why is the export command useful?

Answer 5

If we don’t want to repeatedly type out some sort of string, for example an IP address, the export command allows us to define a variable.

Question 6

How do you define a variable using export?

Answer 6

E.g. export b=192.168.116.114

Question 7

How do you then use that variable in a practical example?

Answer 7

ping -c 10 $b

The variable must have a $ accompanying it.

Question 8

What command and variable do we use to view the current PID (Process ID) of the bash shell?

Answer 8

echo “$$”

Question 9

How do we view all environment variables?

Answer 9

env

Question 10

How do we view command history?

Answer 10

history

Question 11

After viewing the history, what is a fast way to execute a command?

Answer 11

Using the numbers next to the command, type !3 (for example).

Question 12

Where is all command history saved?

Answer 12

In the .bash_history file.

Question 13

What two variables dictate the command history save?

Answer 13

HISTSIZE and HISTFILESIZE

Question 14

What does HISTSIZE do?

Answer 14

Controls the number of commands kept for the current session.

Question 15

What does HISTFILESIZE do?

Answer 15

Configures how many commands are kept in the overall history file.

Question 16

Where are HISTSIZE and HISTFILESIZE stored?

Answer 16

.bashrc - bash configuration file

Question 17

How do we use the reverse-i-search facility?

Answer 17

Ctrl + R

Question 18

What are the three data streams connected to the programs run through bash?

Answer 18

Standard Input (STDIN)
Standard Output (STDOUT)
Standard Error (STDERR)

Question 19

How is piping related to the data streams?

Answer 19

Piping connects the data streams between programs and files.

Question 20

What command counts the words and lines of a document?

Answer 20

wc

Question 21

What is the command for counting the number of lines in a document?

Answer 21

wc -l

Question 22

What is the command for counting the number of characters in a document?

Answer 22

wc -m

Question 23

How do you create a new document through redirecting data streams?

Answer 23

echo “hello bob” > redirection.txt

Question 24

How do you append data using data streams?

Answer 24

echo “hello jane”&raquo_space; redirection.txt

Question 25

What are the file descriptors for STDIN, STDOUT and STDERR respectively?

Answer 25

0, 1 and 2 respectively.

Question 26

How do we redirect error messages?

Answer 26

After a command, use 2>error.txt as an example. | Another example is 2>/dev/null - which is a file used for discard error output.

Question 27

What is an example of piping a command?

Answer 27

cat error.txt | wm -m > count.txt

Question 28

What does the grep command do?

Answer 28

Searches for a line containing a given string of text.

Question 29

What does the i switch for grep do?

Answer 29

Ignores text case in strings.

Question 30

What does the r switch for grep do?

Answer 30

Searches recursively through a file or directory.

Question 31

What does sed do?

Answer 31

sed is a stream editor that performs editing functions on a stream of text.

Question 32

Use an example of the sed command and explain the components.

Answer 32

echo 'I need to try hard' | sed 's/hard/harder/' The single quote starts the argument. s means substitute, hard is the word to replace and harder is the word to replace it with.

Question 33

What does the cut command do?

Answer 33

The cut command extracts a section of text from a line and outputs it to standard output.

Question 34

What does the d switch do in cut?

Answer 34

The d switch defines the delimiter.

Question 35

What does the f switch do in cut?

Answer 35

The f switch defines the field number of the line to cut.

Question 36

Use cut in an example.

Answer 36

echo "I hack binaries,web apps,mobile apps, and just about anything else" | cut -d "," -f 2 the output is "web apps"

Question 37

What is awk?

Answer 37

awk is a data extraction and reporting tool similar to cut.

Question 38

How do we define a field separator (delimiter) in awk?

Answer 38

-F

Question 39

How do we print which field in awk?

Answer 39

'{print $1, $3}'

Question 40

Use awk in an example.

Answer 40

echo "hello::there::friend" | awk -F "::" '{print $1, $3}'

Question 41

What is the main difference between awk and cut?

Answer 41

Cut can only use one character as a delimiter while awk can use multiple.

Question 42

What does the sort command do?

Answer 42

sort the output.

Question 43

What does the uniq command with a c switch do?

Answer 43

uniq -c will prefix each line with the number of occurances.

Question 44

How do we write changes to nano?

Answer 44

Ctrl + O

Question 45

How do we cut the current line in nano?

Answer 45

Ctrl + K

Question 46

How do we uncut the current line and paste in nano?

Answer 46

Ctrl + U

Question 47

How do you search in nano?

Answer 47

Ctrl + W

Question 48

How do you exit nano?

Answer 48

Ctrl + X

Question 49

How do you enter insert mode in vi?

Answer 49

i

Question 50

How do you go back to command mode in vi?

Answer 50

esc

Question 51

In what mode in vi do you need to be in in order to copy, paste and so on?

Answer 51

command mode

Question 52

How do you copy the current line in vi?

Answer 52

yy

Question 53

How do you paste a line you copied in vi?

Answer 53

p

Question 54

How do you delete a current character in vi?

Answer 54

x

Question 55

In vi how do you write the current file to disk (save) and stay in vi?

Answer 55

:w

Question 56

In vi how do you quit without saving?

Answer 56

:q!

Question 57

In vi how do you save and quit?

Answer 57

:wq

Question 58

How do you use compare files using comm?

Answer 58

comm

Question 59

When reading the output for comm, how do you interpret the results?

Answer 59

The first column consists of data unique to the first file. The second column consists of data unique to the second file. The third column consists of data contained in both files.

Question 60

How do we suppress output in comm?

Answer 60

comm -12 will suppress output in the first two columns.

Question 61

How do you use vimdiff to compare files?

Answer 61

vimdiff

Question 62

How do you extract files using tar?

Answer 62

tar -zxvf scans.tar.gz

Question 63

Explain jobs within a linux kernel.

Answer 63

The kernel manages multitasking through the use of processes. The kernel keeps information about each process to keep things organised and assigns each process an identifier or PID.

Question 64

How do we background a job?

Answer 64

While running a command append an ampersand or '&' (no quotes) to the end of it. You'll then be given a PID.

Question 65

How do we suspend a job?

Answer 65

Ctrl + Z

Question 66

Once a job is suspended, how do you resume it in the background?

Answer 66

bg

Question 67

How do you view jobs currently running or suspended?

Answer 67

jobs

Question 68

What command will send a job to the foreground?

Answer 68

fg %1 where 1 is the job number

Question 69

What is ps and how is it different to the jobs command?

Answer 69

ps lists processes running system-wide, not just in the current session like jobs.

Question 70

How do we view all system wide processes with full formatting?

Answer 70

ps -ef

Question 71

If we are looking for a certain process, how do we use the ps command to narrow down the results?

Answer 71

ps -fC

Question 72

How do we kill a process?

Answer 72

After running ps -ef, find the PID number and use the kill command on the number.

Question 73

What does the tail command do?

Answer 73

tail monitors log entries as they are being written.

Question 74

How can we use tail?

Answer 74

sudo tail -f /var/log/apache2/access.log

Question 75

What do the -f and -nX switches in tail do?

Answer 75

-f is used to follow a file as it's updated. -nX is used to output the last X lines instead of the default 10.

Question 76

What does the watch command do?

Answer 76

the watch command runs a designated command at regular intervals. by default it runs every 2 seconds.

Question 77

How do we specify a different interval when using watch?

Answer 77

we use the -n X option to have it run every X seconds

Question 78

Use an example of wget.

Answer 78

wget -O hello.txt www.offensive-security.com/pdf/file.txt

Question 79

What protocols can curl use as opposed to wget?

Answer 79

wget can only use http, https and ftp while curl can use IMAP/S, POP3/S, SCP, SFTP, SMB/S, SMTP/S, TELNET, TFTP. curl is a lot more versatile.

Question 80

Use an example of curl.

Answer 80

curl -O hello.txt www.google.com/drive/dog.txt

Question 81

What does the HISTCONTROL variable do?

Answer 81

defines whether or not to remove duplicate commands, commands that begin with spaces from the history, or both

Question 82

How can we use the HISTCONTROL variable to remove duplicates?

Answer 82

export HISTCONTROL=ignoredups

Question 83

What does the HISTIGNORE variable do?

Answer 83

filtering out basic commands that are used frequently such as cd, ls, pwd etc.

Question 84

How do we use HISTIGNORE?

Answer 84

export HISTIGNORE="&:ls:[bf]g:exit:history"

Question 85

What is an alias?

Answer 85

An alias is a string that replaces a command that we define ourself.

Question 86

How is an alias different to a variable?

Answer 86

An alias utilises a string to execute a command with it's switches and arguments. A variable is a string.

Question 87

Demonstrate the use of an alias command.

Answer 87

alias lsa='ls -la'

Question 88

Alias don't have any restrictions. For example, if mkdir was accidently aliased as ping -c 400 localhost, the consequences would be a lose of function. How do we counter this?

Answer 88

Either exit the bash session or use unalias mkdir.

Question 89

If we want an alias to be persistent, what do we do?

Answer 89

Place the alias into the .bashrc file in the /home/kali directory.