Shell Scripting Tutorial-18: Shell Variables; Grab User Input Using 'read' Video Lecture | Shell Scripting: Discovering to Automate Command-Line Tasks - Back-End Programming

hello guys my name is mother and welcome
to my channel this is the 18th tutorial
in this series of tutorials on UNIX
shell scripting in this tutorial we're
going to continue our discussion on
shell programming and we prepare another
shell script we learned about shell
variables and we also learn how to take
input from users using the beat command
now what is a variable variable is
basically a place in memory where you
can store things and think of it as a
container just as you can use a
container to store cookies or miracle
fruits you can use variable to hold
strings of text or numbers now a shell
variables have you know certain
properties and there are certain rules
that you must obey before creating your
variables it's very important to know
those rules for example the name of a
variable can start either with an
alphabet or the underscore symbol you
cannot have numbers as the first
characters in your variable names and
the other thing that you must remember
is that variable names are case
sensitive and what I mean by that is
that my underscore there is different
from my underscore right so those are
two different variables and you can use
both those variables in a single script
and commas or bad blank spaces are not
allowed so this would be an illegal
variable name like my space but you know
when the shell would encounter this it
would you know find this erroneous and
yeah that's pretty much it those are the
few rules that you need to remember you
know you can use underscore character as
the first character in your variable
so underscored where one this is allowed
right and yeah that's it and now we are
going to discuss the read command now
what I'm going to do in this tutorial is
I'm going to first use echo to display a
message on screen and before doing that
I'm going to save this file as as SS 3
dot SH in my home directory okay there
you go
save now and you can see that my text
editor highlights echo and I'm going to
display a message like please enter your
name right and the echo command
by default puts a newline character at
the end of the string that you put
within the double quotes so the next
thing or you know if suppose you put an
echo statement on this line as well then
it would automatically be displayed on
the next line right this is different
from the programming languages with
which I've worked so you know I just
thought I should mention it to you guys
now what I'm going to do is I'm going to
use a command called read and I'm going
to use a variable name called my
underscore name that is my variable name
and I don't have to put a semicolon and
in the next line I'm going to again use
an echo statement and I'm going to
display hello and I'm going to use a
dollar symbol now this is important
whenever you call a variable in your
program whenever you try to access it
then you have to use a dollar symbol
before typing the name of your variable
so I've used a dollar symbol here and
I'll type in the name
which is my underscore name and then
I'll use a comma and then I'll just uh
you know type in some more text like
it's fine day isn't it
right that's pretty much it and for my
first statement I'll put a comment like
this script demonstrates the usage of
read come on yeah that's it and I'll
save this fire and I'll open my terminal
now and it's fresh and ready waiting for
me to shoot a command a date and I'm
going to use SH typing the name of my
file which is SS 3 dot SH and there you
go you see that my first statement which
was a echo command and the statement was
entering your name it's a it's flashing
on screen for me and the shutter is
waiting for me to input something I'm
just going to type in my name here
mother and when I press the Enter key I
see this message hello mother it's a
fine day isn't it now what has happened
here is that my script got executed and
at first this statement was ignored
because it is a comment the next
statement is the echo statement it got
executed and this sentence got printed
on screen please enter your name and
then as I said each echo statement is
terminated by default with a newline
character so the cursor was blinking on
the next line in the shell waited for me
to provide input and then whatever I
typed and I typed my name mother it got
stored in this variable my underscore
name and then the next statement is
again an echo statement and first hello
was displayed and then the shell saw the
dollar symbol and understood that what's
going to follow is a variable name so
it's searched in its memory for the
variable my underscore name and it found
that its contents had my name and it
basically replaced this entire thing
with my name and then it printed the
rest of the sentence in that
so there you go you've now understood
about shell variables and you've also
seen how to use the read statement to
take input from people from users of
your program in your search in your
shell scripts so that's it for now I'll
see you guys in the next tutorial thank
you so much for watching this one and
please subscribe to my channel