Understanding the Shell Environment

Question 1

What is the shell?

Answer 1

The Shell is a binary application to interact with the system directly. It is a text mode interface

Question 2

What is the default shell in SUSE?

Answer 2

The default shell in SUSE is bash

Question 3

Where can you see the available shells?

Answer 3

Available shells are in /etc/shells

Question 4

What command shows the aliases for the user?

Answer 4

The command #alias give you the list of aliases for the user

Question 5

What type of variables are there?

Answer 5

There are shell variables and environment variables

Question 6

What are functions?

Answer 6

Functions are like script-like grouping of commands

Question 7

What is an alias?

Answer 7

They are like shortcuts to larger commands

Question 8

What are the shells modes?

Answer 8

Login, via ssh, using su - or sudo -I

Non-login, using su

Interactive when you execute a command

Non-interactive when you run remotely ssh user@host “somecommand”

Question 9

What are the files used for interactive logins?

Answer 9

/etc/profile and .profile are used for interactive logins

Question 10

What are the files used for non-interactive logins?

Answer 10

/etc/bash.bashrc and .bashrc as used for non-interactive logins

Question 11

What man page gives you info about the shell?

Answer 11

man bash

Question 12

What command shows you the list of files you have run?

Answer 12

history

Question 13

What files keeps the history in store?

Answer 13

The file /home/user/.bash_history keeps the history

Question 14

How do you re-run command 77 in the history?

Answer 14

!77

Question 15

What keys do you have to use to re-run the last command you ran?

Answer 15

To re-execute the last command just type !!

Question 16

What do variables contain?

Answer 16

Variables contain data

Question 17

What command can you use to see the variables?

Answer 17

echo $VAR_NAME

Question 18

What command can you use to see ALL the variables?

Answer 18

env

Question 19

What command displays all variables and functions?

Answer 19

set

Question 20

To set a variable, run this syntax:

Answer 20

VARIABLE=content

Question 21

To make a brand new variable available to all shells, you have to…

Answer 21

export it:
#export VAR=content

Question 22

Special variables are:

Answer 22

$? shows the exit code of the previous command
$0 shows the name of the command executed
$* shows all the arguments a command had
$# shows how many arguments were used
$$ shows the PID of the shell you are in

Question 23

Which are the exit code values?

Answer 23

0 means no errors, zero errors

Something else, usually 127 or 1 means an error in command just run

Question 24

Piping and redirection uses these values:

Answer 24

Stdin, 0, accepts input from pipes

Stdout, 1, is displayed or piped

Stderr, 2, is printed on the screen

Question 25

what is the bit bucket?

Answer 25

/dev/null is the bit bucket in the system

Question 26

What is the difference between > and >> ?

Answer 26

> writes and overwrites if done twice in a row >> appends

Question 27

What does this do? 1> /file

Answer 27

writes stdout to a file

Question 28

What does this do? 2>/dev/null

Answer 28

sends stdout to the bit bucket

Question 29

What does this do? 2>> /file

Answer 29

appends to a file

Question 30

What does this do?

Answer 30

sends a file as stdin to a command

Question 31

What does the #tee command do?

Answer 31

The #tee command is a splitter, so, it lets the initial command print the stdout to the screen and writes that same stdout to a file.

Question 32

What is the syntax of the #tee command?

Answer 32

``` #find /home -type f -iname Jose.txt | tee jose_file /home/Jose.txt ```

Question 33

How can you run 2 or more unrelated commands in the same command line

Answer 33

use a semi-colon between the commands (;)

Question 34

How can you run 2 or more unrelated commands in the same command line?

Answer 34

You can do the same with && but they will both show in the screen only if the first command actually succeeds. If the first command fails, the sequence stops:

Question 35

What does this do? ||

Answer 35

|| a double piple between 2 commands means to run the second command only if the first one fails

Question 36

What does this command do? cp /dir1/* dir2

Answer 36

it copies only the files within dir1 and not the directory itself

Question 37

Does the #mv command use the same inodes before and after the move?

Answer 37

the mv command uses the same inode numbers before and after the move

Question 38

Is #mv recursive by default?

Answer 38

mv is recursive by default

Question 39

Can #rm remove non-empty directories?

Answer 39

no, for that use # rm -rf

Question 40

To remove the contents of a directory, but not the dir itself, do:

Answer 40

rm -rf dir2/dir1/*

Question 41

In case the dir you want to delete is not empty, use:

Answer 41

rmdir --ignore-fail-on-non-empty dir_name

Question 42

What info does the #stat command display?

Answer 42

stat give you links, perms, size, access, modify, change timestamps, block size, etc

Question 43

What time stamp does # cat change?

Answer 43

cat changes the access time

Question 44

What time stamp does # chmod change?

Answer 44

chmod changes the modify time

Question 45

What time stamp does #ls -l display?

Answer 45

ls -l always shows the modify time

Question 46

Does writing content inside a file change the change timestamp?

Answer 46

yes

Question 47

to reset your terminal, use the command...

Answer 47

#reset

Question 48

What is the command that refreshes a command o/p every 2 seconds?

Answer 48

watch refreshes the stdout every 2 seconds for a command. #top has watch integrated

Question 49

What are common options for the find command?

Answer 49

- name - iname - newer: searches for a file newer than a given file - user - exec runs a command against that the find command found, remember it finishes with \;

Question 50

What does grep do?

Answer 50

it fetches contents of files based on the arguments/options given

Question 51

What are some grep options?

Answer 51

- i case insensitive - r recursively searches throught a target directory - n shows the line number of the search result at the beginning of each line in the stdout - v inverts the search, shows all BUT the string - w searches for whole words only, exact string match only

Question 52

What is the difference between archiving and compressing?

Answer 52

archiving: tar, same size as original file compressing: does compress

Question 53

Name a few common tar options

Answer 53

cvf new.tar things_to_tar xvf file_to_extract.tar tf file.tar

Question 54

Syntax of compression:

Answer 54

gzip: tar -czvf new.tar.gz directory_to_compress bzip2: tar -cjvf new.tar.bz2 directory_to_compress xz: tar -cJvf new.tar.xz directory_to_compress

Question 55

to see the contents of the compressed tar:

Answer 55

tar -tzvf tar -tjvf tar -tJvf

Question 56

What happens if you don't tar something and just compress it?

Answer 56

if you don't tar something and just compress it, the compression tool will replace the original file (gzip does not compress directories) You have to tar them first