Original subtitles

1

Hello everybody and welcome to part two of

this tutorial. Let's go ahead and save the

2

file. Press control-O to output the file.

It says file filename to write. You can actually

3

modify it here. You can type in some letters

or whatever you want to change the name here.

4

You can even change the extension if you want.

There is no need for the time being. I'm just

5

going to go ahead and save it as "test." Just

press enter. There you go. It says, "wrote

6

one line. Hit control-X to exit. There we

go. Clear the screen. Now, I'm going to use

7

cat command to get a listing of this particular

file, which is far more reasonable than the

8

previous one, which you couldn't read. The

command, by the way, was functioning properly

9

but it was mostly a binary file. Therefore

I mean, it gave you listing but you couldn't

10

really read anything from it. So just go ahead

and type in cat test and there we go. It says,

11

"some random text goes here." That is the

text that we have typed into the test file

12

and you can cat it like this. These things

are very good, especially with files that

13

you want to make sure not to change them in

any way, you don't want to make any accidental

14

changes or anything of the kind and you want

to quickly see what is located within that

15

file. There is another way of doing this.

Basically, it's "ls." Let's go ahead and get

16

over to "cd etc/apt/." "Ls." We have plenty

of files to work with. Let's take sources.list

17

as an example here. So if I do "cat sources.list"

I'm going to get everything that is within

18

that file as before. It is listed in my terminal,

it's here to stay. It's not going anywhere.

19

There is another command which I could use.

Just go ahead and clear the screen. It is

20

called "less." If I type, "less sources.list"

I will be prompted with a new tab where I

21

can actually view things here. Not a new terminal

tab, but a new workspace within the within

22

the terminal itself. When I press Q I exit

and nothing will be displayed here. So very

23

nice in terms of being neat, organized and

so on and so forth. So less and cat are very

24

nice things. You can use, for example, "cat

sources.list" and the command that I have

25

previously mentioned is "grep." "Grep" means

you pull something, grep something from somewhere

26

else. Here's what I mean by it. Type in "cat

sources.list" and you type in a pipe. This

27

symbol here. It's called a pipe which basically

states whatever the output of this is pipe

28

it to whatever command comes here. So, I'm

just going to type in "grep" and let's say

29

I want to type in, "src." Press enter. Excellent.

So it will only print lines that have "src"

30

in them. Linux is case-sensitive. When you

are grepping, it's going to check whether

31

it's lowercase or not. You can give it an

ignore case. You can type this, "-i" to ignore

32

the case. This time, you're going to get the

same output because there are no different

33

things within this file. You get the general

idea. So this is how you would use "cat" with

34

grep to pull things out of a file. Very important.

This is a huge part of the Linux terminal--

35

filtering through text files. Primarily because

we are going to be doing large network scans

36

and we will want to create files from which

we will be able to pool useful information.

37

We will later in turn pass this information

to other tools to do something with. Anyway,

38

just go ahead and clear to screen for the

time being. You also have "echo." Type "echo

39

"I AM ALIVE"." It will echo these words it

literally is an echo. You type something into

40

it and it echoes them here. Let's go back

to the home directory, get a listing and use

41

exactly the same command echo live. By the

way, you can scroll through previous commands

42

by using arrow key. So using the up arrow

key or the down arrow key, you can scroll

43

back through previous commands and you don't

need to retype them. So I am alive. I'm going

44

to insert this. I will use a ">" and type

in "test." This will echo "I AM ALIVE" into

45

test. It has replaced the contents of the

test, which was "some random text goes here"

46

into, "I AM ALIVE." Very nice command to have.

You can change variable names, variable values

47

with echo and so on and so forth. We will

use this a bit more as we progress through

48

the course. I don't really want to get in-depth

here. Primarily because later on when we have

49

clear examples that directly relate to what

we are doing, which is basically testing,

50

then you will see more advanced usage of pretty

much all of these commands-- especially grep.

51

You have "touch."Touch" is a quick way to

create files. So, for example, I can type,

52

"touch file1 file2 file3." Press enter, "ls."

You see, it immediately created three files.

53

That is a very quick method to create any

amount of files. You can specify a folder.

54

You can create this file in home, this one

in var, this one in varlog, and so on and

55

so forth. Down below, you have "mkdir." Type

in, "mkdir" and it makes a directory. So you

56

are making some sort of a directory. Let's

say this the name of this directory will be

57

"placeToBe." If I hit "ls." There we go. It

states that is the does that this file is

58

actually a directory, which is PlaceToBe.

I can even navigate to it and say, "PlaceToBe

59

ls." There is nothing in it but you get the

idea. You can make directories in such a fashion.

60

Now, if I type "chown" it allows you to change

the ownership of a particular file. Since

61

we only have a single user here, which is

root, there isn't really any point in doing

62

so. If we create some of the new users we

could do that. However, we don't need them.

63

I'll just show you how this would work. For

example, if the owner of the file was not

64

root and you want to change it to root, do

the following. Type, "chown," then you would

65

type the username ":" and the user group.

The user group and the username are usually

66

the same on your home PC, unless you have

some bigger servers or something like that.

67

Then just specify the name of the file. You

can type "test." There it will effectively

68

change the ownership of file test to the username

root, who is from the user group root. If

69

I do "ls la" it states who the owners are

and which groups actually owned the files

70

as well. Clear the screen. There is another

more used command. It's called "chmod." This

71

command allows you to change file permissions.

This is something that you will need to use

72

on daily basis and quite often. Primarily

because, you see if I have an executive file

73

in Linux, for example. Let's just go ahead

and type in, "echo hello." I want to that

74

to test and I want to test to test.sh. "Sh"

is basically an executable one, that's a bash

75

script for Linux that in such a way you can

automate tasks. We will deal with it in greater

76

depth as we proceed through the tutorial.

You will need to be acquainted with bash scripting

77

definitely. Bash scripting is very similar

to the terminal itself, so pretty much all

78

the commands used in the terminal, can be

used by scripting as well. You basically just

79

combine a bunch of them in a file. Now, I

want this to be my executable, but you see

80

the way to to start executables is "./" as

stated previously that's the command to start

81

any executable. If I type in test, and press

that, it doesn't give me a list of possibilities.

82

Now, surely test.sh is an executable, but

no you see, it doesn't have a permission to

83

be an executable file. See here the difference,

take a look at this file and take a look at

84

this file. This one is green, this one is

not. Now look at their permissions. So you

85

see, it has a markation that is executable

for all groups, users, etc., while this one

86

up here does not have such permissions. You

need to change that. What you do to change

87

it is, "chmod." You would type in, "+x." If

you want the file to be writable you type,

88

"+w," if you want it to be executable "+x,"

if you want to be able to read the file, "+r,"

89

very simple. There is also a way of doing

this with numbers. You can type in, "755."

90

Don't try remembering all those modes. Whatever

you need go on the internet and check. It

91

can be quite complicated, but these three

you need to know: +x, +r, and +w. Also 777,

92

which is a global mode. This is the mode which

is not recommended for actual usage, but you

93

use "chmode" to actually test or troubleshoot

things. For example, if you want to be absolutely

94

sure that certain actions are not being prevented

due to file permissions, you change the mode

95

of those files to 777, which is the global

mode that anybody can do anything with the

96

file. If you still have an error message you

know that it is absolutely not related to

97

anything in regards to permissions. So, those

four things to do need to know. You can just

98

go ahead and type, "chmod +x test.sh," press

enter. If I do "ls la" once again, you will

99

see that test.sh is now executable. Let me

just run it and there you go. If I run this

100

it's going to echo "hello" on my terminal

screen. There's a bit more to go. Not much

101

more left. There is just one more command

that I would really like show you. This can

102

be a very dangerous command. Indeed, it can

mess you up in ways you can't begin to imagine

103

yet. that is the command "rm." "Rm" is basically

remove. Once you remove things with this command,

104

it's next to impossible to recover pretty

much anything. So, if I type in, "rm test.sh,"

105

it's going to remove it. It's no longer going

to be there. If I go ahead and navigate over

106

to PlaceToBe and I "touch test" to make a

new file there. If I go ahead and say "RM

107

PlaceToBe." It will say "rm cannot remove

place to be because it is a directory." This

108

is a failsafe of the rm. So, you wouldn't

delete a full directory because you will be

109

able to recover it, and that would be really

bad. What you can do is type in, "rm -f PlaceToBe."

110

Cannot remove directory. Okay, no problems.

Sometimes you get stuck. I'm deliberately

111

going to leave this part in the tutorial.

I'll just troubleshoot it. So you type in,

112

"--help." Here you have recursive remove directories

and their contents recursively. So, that's

113

a very nice option. So, let's just go ahead

and do that because this will go into the

114

folder and remove everything within the folder

and the folder itself, hopefully. So, just

115

go ahead and type in, "rm -r PlaceToBe," press

enter. There you go. It has deleted it. There

116

we go, it is no longer there. The "-f" that

I have used is force. It will not ask you

117

any questions. It will delete the folder or

file, which can be also very dangerous. When

118

you're using "rm," you always want to be asked

questions. In any case, as I said, I deliberately

119

left his to show you that even if you get

stuck worry about it. I get stuck all the

120

time. If you don't know what to type in, what

argument to pass, just type in "--help." Take

121

a look at what you can actually type, read

a little bit and then use the options. Try

122

it out, sometimes it will work, sometimes

it won't. More often than not, you will be

123

able to figure it out from the help menu.

If you can't figure it out from help menu,

124

just typed in "man rm" and you can read pretty

much everything there is to know about this

125

command here. If you really can't perform

the task, if you can find anything useful

126

here, forums are your next best bet. Trust

me you will succeed in doing it. In any case,

127

this was a brief introduction some of the

basic commands that we will use. Please make

128

sure that you know what each one of these

commands does, at least basic functions. Later

129

on we will get in-depth, do more advanced

stuff and use more advanced commands by combining

130

them, and so on. In any case, I bid you all

farewell. I hope to see you in the next tutorial.