Linux - Set variables

so into our previous video we have seen

how we can run a small shell script file

where have added simple commands and

pose that I have just run the command

now what if I want to store something

somewhere so that into the program I can

use those particular date again now for

example you have a huge host name or

hostname which you cannot remember so we

can use it later so that I can host or

we can save those particular host name

into a particular variable or I can take

an example if you have an address and in

the form or in a program you want to add

your address multiple thing if you want

to add those multiple at your address

into multiple lines what will happen you

have to type everything every time if I

don't want to type it again and again

what I can do I can store it somewhere

with some letters variable and the data

which you are going to add now here an

example like your address that forbid a

value so we can add any value to any of

the variable so that into the program I

can use the variable instead of value

which reduces my program size and my

efforts that is the task of your

variable and that is the variable which

we use now if I'm talking about

variables again we have different type

of variable declaration now here the

variables can be declared for a local

local purpose means if I am using a

variable I can use within a program only

once that is a local variable now if

suppose I have created a program where I

have a sub programs of those particular

programs so I want to declare those

particular variables every time into

these sub programs know I can inspite I

can define a environmentally variable

and water mental variable means I can

set a value in particular main program

post that if you have some deviation of

those programs they can again call this

particular variable which is called as

an environment variables so environment

variables can be used into these sub

programs into that particular program

itself the next we have that is called

as a shell variable so shell variable

be using any of the programs into your

Linux operating systems

so basically shell variables are by

default declared they are declared by

the Linux itself even though if I want

to add some shell variables I can even

add the two which can be called into any

of the programs any of these sub

programs created into the same terminal

different terminal same location or a

different term location that the reason

there's also called as a global variable

so here we have three type of variables

local environmental and your shell

variable let us let us see how we

generally use this variables into our

program and create a program by using or

setting the variables into it so let us

begin with our terminal so in our

previous video we have seen how we can

create a sample file a sample file which

we have created that was again

containing a variable which we have

already discussed like we have a code a

particular text that I am asking my user

to enter his first name so when the user

enters first name that is accepted into

the variable a so this is a variable and

I'm adding the value to this variable

and letter to it I'm going to print echo

hello and this variable name the same

way we can create more variable files

like for example I am going to create a

name dot SH file now for example I do

not want my user to enter the name right

so I can also run hello

you are talking to

you

Church shapes right and same way we can

read it by you know I don't have to read

it i anything here so just so I'm

defining our name like you know a text

that is you are talking to your mr.

James and we can also define the

designation of this person designation

equal to whatever the designation he has

like for example senior or we can say

CEO of the company that we need to

define and to the courts

and then we can say his contact number

you

okay so this is his contact number now I

want this again to be displayed so I'll

be using it as echo and my designation

and the company it should be displayed

to the user now else I can give comma

and we can define designation so

generally here this designation and this

contact is the variable and I want to

print this particular thing same way we

can also define echo

you can contact me at and then I'll

define contact done and just I'm going

to save the file now let's see how

generally this particular file runs so

here I should get it come on I should

get this message you are talking to mr.

James my resignation in the company is

CEO of the company and you can contact

me at this number so let us check I'll

just run this file and see I got the

complete text right now it's suppose I'm

using this particular file itself named

or as such and someone lecture on has

changed the designation like you know

here somewhere someone has changed or

added his own designation for example I

just find echo I am an assistant

managed

okay then he again he added the

designation our technician it goes to

assistant manager okay I'm just going to

define the name Jones okay

and then as contact number

you

I can't sir there's SS contact number

again you want to print the same thing

as king you're fine the second Asian

again echo contact number

Quan Chi so generally you can see now

what happened I have saved the two

values over here the mr. Jones you know

designation and contacts over here into

the same variable and the programmers

Pig will just assume the program is a

huge program and later on even the

assistant manager Jones has added his

designation in the same variable now

what is going to happen that we are

going to see into the output

okay now I'm going to run the same you

can find it is giving you this part as

this but while I type over here you know

I get the message mr. assistant roll my

it is again accepted as it is not a

variable and post that again we've all

found that there isn't some error rate

of all there will be and there is

actually a different error we have got

here

[Music]

you

there are actually the characters which

we use use a several different kind of

so let us check now I've just changed it

name dot I searched and I can find found

contact number is this one this contact

number is this one let us check that is

again error which we found so so you can

also check for the errors and really get

formed so this is the assistant manager

we need to define it cold patience right

as we are using more than one word down

with that know everything else is ready

again name dot Sh

all right so it's showing you the skirt

again it is not showing you the company

name right so this is the company name

oh there is a CEO of the company here

again if you have some mistake it's not

displaying or designation and most

probably it also happens like you know

if you give the same contact numbers now

and the same variables sometime it might

display you the wrong entries correct so

that's reason like for example into this

the name dot as such I want to display

just display

designation

chin and a contact number at the end now

what is going to display that we are

going to check here which display which

our designation will be seen over here

that we need to check you can see it is

showing you the designation of your

assistant manager right means I want to

become to know like you know why this is

completely skipped so it is taking the

latest one that is is assistant manager

now for avoiding such reason if you know

such happenings like where the complete

variable is getting overlapped with

something else so what you can do is you

can make your variable read-only so what

will happen you can see

so for making your variable read-only

what you need to do is just after

defining the variable you need to define

read-only there's a mention same way

read-only

on cat

our

and now see what happened I'll save the

file I'll hit enter

I'll give come on name God as such so

it's giving me an error that the

variable which we have used for your

assistant manager for defining his

designation and defining his contact

cannot be used because they are the read

only variable so when we run or we know

when we run a file or when we run a

script will come to know like why we are

not able to provide designation so that

this user can move into thee again

descript file called as named or as such

and he has to change the designation

variable with a different name like we

can also change it with

any other available

you

that's it chin and

and for contact Hagan use font and here

again you can display in the same way

and again so much like and check giving

a such name daughter such now it should

not give you error but now here it is

showing you the correct now contact

number and you know the designation of

your mr. Jones that means here the entry

is what we have you know the variables

what we have added over here they are

made read-only so that someone else in

the near future and that the same scrub

should not use the same variable for

storing the other value because the

variables generally we are using over

here there are a scalar variables means

at the time they can store only one

value so that's a reason in the last

line when we have given the command or

when we have you know a printer to the

designation as well as in contact of

your name dot as such it frenches me

with the designation last time of these

last designation which we have added but

now as I made it read-only and I have a

particular you know individual variable

and individual variable contain our

individual value that's the reason we

are able to producing so it is you know

recommended that whenever you declare

your variable into you know a script

when you come to know that the Skyrim

script might be used by many other

people and you can also you know forget

what the variables you have used earlier

so what you can do you can make your

readable variables so this is how

generally we use the variables now again

we can use a particular command called

as unset so that if suppose I do not

want to set a variable for example the

same file I'm going to open a name dot

as such and later on I want to use these

variables that is contact and

designation for example he has already

designed so I'll just comment this

correct so for unsetting this particular

variables either we can directly comment

out everything or what we can do is we

can give the command unset Oh

variable name so it will automatically

unset a variable so even after that if I

right to pin or you know get access to

the variable value that is like it

should not print anything right so just

a sec I need to provide the dollar sign

if I want to run a particular variable

and this is again unset it is yes I see

so I'm just going to define this

variable I want one set I do not want to

display this particular variable but I

want to display the other variable which

I have right now that is a kill

dollar and your

once we have done with that I'm going to

save the same and hit enter let us run

the file again and such name dot Sh

you can find the contacts as in

displayed the designation is not

displayed because I have unset that

particular variable along with that we

can see the other data is what we have

so here we have seen how we can set up

variable that is your scalar variables

we have also seen like how we can you

know make a variable read-only so that

no one else can replace your value of

that particular variable along with that

we have also seen how we can print a

variable and unset a variable so this is

we have talked about the variables which

we can add into our shell script and how

we generally use it so into next video

we are going to see more of your shell

scripting so keep watching