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Linux - Set variables
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0:00
so into our previous video we have seen
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how we can run a small shell script file
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where have added simple commands and
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pose that I have just run the command
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now what if I want to store something
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somewhere so that into the program I can
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use those particular date again now for
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example you have a huge host name or
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hostname which you cannot remember so we
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can use it later so that I can host or
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we can save those particular host name
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into a particular variable or I can take
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an example if you have an address and in
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the form or in a program you want to add
0:35
your address multiple thing if you want
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to add those multiple at your address
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into multiple lines what will happen you
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have to type everything every time if I
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don't want to type it again and again
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what I can do I can store it somewhere
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with some letters variable and the data
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which you are going to add now here an
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example like your address that forbid a
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value so we can add any value to any of
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the variable so that into the program I
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can use the variable instead of value
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which reduces my program size and my
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efforts that is the task of your
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variable and that is the variable which
1:11
we use now if I'm talking about
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variables again we have different type
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of variable declaration now here the
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variables can be declared for a local
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local purpose means if I am using a
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variable I can use within a program only
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once that is a local variable now if
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suppose I have created a program where I
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have a sub programs of those particular
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programs so I want to declare those
1:35
particular variables every time into
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these sub programs know I can inspite I
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can define a environmentally variable
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and water mental variable means I can
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set a value in particular main program
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post that if you have some deviation of
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those programs they can again call this
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particular variable which is called as
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an environment variables so environment
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variables can be used into these sub
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programs into that particular program
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itself the next we have that is called
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as a shell variable so shell variable
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be using any of the programs into your
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Linux operating systems
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so basically shell variables are by
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default declared they are declared by
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the Linux itself even though if I want
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to add some shell variables I can even
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add the two which can be called into any
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of the programs any of these sub
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programs created into the same terminal
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different terminal same location or a
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different term location that the reason
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there's also called as a global variable
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so here we have three type of variables
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local environmental and your shell
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variable let us let us see how we
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generally use this variables into our
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program and create a program by using or
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setting the variables into it so let us
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begin with our terminal so in our
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previous video we have seen how we can
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create a sample file a sample file which
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we have created that was again
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containing a variable which we have
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already discussed like we have a code a
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particular text that I am asking my user
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to enter his first name so when the user
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enters first name that is accepted into
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the variable a so this is a variable and
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I'm adding the value to this variable
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and letter to it I'm going to print echo
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hello and this variable name the same
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way we can create more variable files
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like for example I am going to create a
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name dot SH file now for example I do
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not want my user to enter the name right
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so I can also run hello
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you are talking to
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you
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Church shapes right and same way we can
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read it by you know I don't have to read
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it i anything here so just so I'm
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defining our name like you know a text
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that is you are talking to your mr.
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James and we can also define the
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designation of this person designation
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equal to whatever the designation he has
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like for example senior or we can say
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CEO of the company that we need to
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define and to the courts
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and then we can say his contact number
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you
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okay so this is his contact number now I
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want this again to be displayed so I'll
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be using it as echo and my designation
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and the company it should be displayed
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to the user now else I can give comma
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and we can define designation so
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generally here this designation and this
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contact is the variable and I want to
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print this particular thing same way we
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can also define echo
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you can contact me at and then I'll
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define contact done and just I'm going
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to save the file now let's see how
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generally this particular file runs so
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here I should get it come on I should
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get this message you are talking to mr.
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James my resignation in the company is
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CEO of the company and you can contact
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me at this number so let us check I'll
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just run this file and see I got the
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complete text right now it's suppose I'm
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using this particular file itself named
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or as such and someone lecture on has
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changed the designation like you know
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here somewhere someone has changed or
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added his own designation for example I
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just find echo I am an assistant
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managed
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okay then he again he added the
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designation our technician it goes to
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assistant manager okay I'm just going to
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define the name Jones okay
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and then as contact number
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you
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I can't sir there's SS contact number
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again you want to print the same thing
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as king you're fine the second Asian
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again echo contact number
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Quan Chi so generally you can see now
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what happened I have saved the two
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values over here the mr. Jones you know
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designation and contacts over here into
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the same variable and the programmers
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Pig will just assume the program is a
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huge program and later on even the
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assistant manager Jones has added his
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designation in the same variable now
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what is going to happen that we are
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going to see into the output
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okay now I'm going to run the same you
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can find it is giving you this part as
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this but while I type over here you know
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I get the message mr. assistant roll my
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it is again accepted as it is not a
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variable and post that again we've all
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found that there isn't some error rate
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of all there will be and there is
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actually a different error we have got
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here
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[Music]
9:09
you
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there are actually the characters which
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we use use a several different kind of
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so let us check now I've just changed it
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name dot I searched and I can find found
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contact number is this one this contact
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number is this one let us check that is
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again error which we found so so you can
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also check for the errors and really get
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formed so this is the assistant manager
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we need to define it cold patience right
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as we are using more than one word down
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with that know everything else is ready
10:00
again name dot Sh
10:05
all right so it's showing you the skirt
10:09
again it is not showing you the company
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name right so this is the company name
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oh there is a CEO of the company here
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again if you have some mistake it's not
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displaying or designation and most
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probably it also happens like you know
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if you give the same contact numbers now
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and the same variables sometime it might
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display you the wrong entries correct so
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that's reason like for example into this
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the name dot as such I want to display
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just display
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designation
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chin and a contact number at the end now
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what is going to display that we are
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going to check here which display which
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our designation will be seen over here
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that we need to check you can see it is
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showing you the designation of your
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assistant manager right means I want to
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become to know like you know why this is
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completely skipped so it is taking the
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latest one that is is assistant manager
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now for avoiding such reason if you know
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such happenings like where the complete
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variable is getting overlapped with
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something else so what you can do is you
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can make your variable read-only so what
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will happen you can see
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so for making your variable read-only
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what you need to do is just after
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defining the variable you need to define
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read-only there's a mention same way
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read-only
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on cat
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our
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and now see what happened I'll save the
12:07
file I'll hit enter
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I'll give come on name God as such so
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it's giving me an error that the
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variable which we have used for your
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assistant manager for defining his
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designation and defining his contact
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cannot be used because they are the read
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only variable so when we run or we know
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when we run a file or when we run a
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script will come to know like why we are
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not able to provide designation so that
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this user can move into thee again
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descript file called as named or as such
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and he has to change the designation
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variable with a different name like we
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can also change it with
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any other available
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you
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that's it chin and
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and for contact Hagan use font and here
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again you can display in the same way
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and again so much like and check giving
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a such name daughter such now it should
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not give you error but now here it is
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showing you the correct now contact
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number and you know the designation of
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your mr. Jones that means here the entry
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is what we have you know the variables
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what we have added over here they are
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made read-only so that someone else in
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the near future and that the same scrub
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should not use the same variable for
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storing the other value because the
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variables generally we are using over
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here there are a scalar variables means
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at the time they can store only one
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value so that's a reason in the last
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line when we have given the command or
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when we have you know a printer to the
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designation as well as in contact of
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your name dot as such it frenches me
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with the designation last time of these
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last designation which we have added but
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now as I made it read-only and I have a
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particular you know individual variable
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and individual variable contain our
14:31
individual value that's the reason we
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are able to producing so it is you know
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recommended that whenever you declare
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your variable into you know a script
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when you come to know that the Skyrim
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script might be used by many other
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people and you can also you know forget
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what the variables you have used earlier
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so what you can do you can make your
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readable variables so this is how
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generally we use the variables now again
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we can use a particular command called
15:01
as unset so that if suppose I do not
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want to set a variable for example the
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same file I'm going to open a name dot
15:09
as such and later on I want to use these
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variables that is contact and
15:20
designation for example he has already
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designed so I'll just comment this
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correct so for unsetting this particular
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variables either we can directly comment
15:30
out everything or what we can do is we
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can give the command unset Oh
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variable name so it will automatically
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unset a variable so even after that if I
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right to pin or you know get access to
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the variable value that is like it
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should not print anything right so just
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a sec I need to provide the dollar sign
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if I want to run a particular variable
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and this is again unset it is yes I see
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so I'm just going to define this
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variable I want one set I do not want to
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display this particular variable but I
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want to display the other variable which
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I have right now that is a kill
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dollar and your
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once we have done with that I'm going to
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save the same and hit enter let us run
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the file again and such name dot Sh
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you can find the contacts as in
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displayed the designation is not
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displayed because I have unset that
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particular variable along with that we
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can see the other data is what we have
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so here we have seen how we can set up
16:45
variable that is your scalar variables
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we have also seen like how we can you
16:49
know make a variable read-only so that
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no one else can replace your value of
16:54
that particular variable along with that
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we have also seen how we can print a
16:58
variable and unset a variable so this is
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we have talked about the variables which
17:03
we can add into our shell script and how
17:08
we generally use it so into next video
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we are going to see more of your shell
17:13
scripting so keep watching
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