Shell Scripting Tutorial-30 Run Checks on Numbers Video Lecture - Shell

hello guys my name is mother and welcome
to my channel this is the thirtieth
tutorial in the series of tutorials on
UNIX shell programming in this tutorial
we're going to learn a couple of things
firstly we're gonna learn to run checks
on numbers and secondly we're going to
learn to use the if-then île if as
selection construct in our shell scripts
so what I'm gonna do is I have my text
editor here I'm going to bring it up and
I've already saved this file as a test
or SH in my home folder right so what
this script is going to do is it's going
to ask the user to enter a number
between 10 and 20 and then it's going to
check if the number is less than 10 if
it is that it will display a message it
will then check if the number is greater
than 20 and if it is then it display
another message and lastly it will
display a message if the number is
indeed between 10 and 20 right so
firstly I'm going to use echo and I'm
gonna ask the user to enter a number so
this is going to be a message for the
user and enter a number between 10 and
20 this is what we're going to display
and maybe I'll use the slash the escape
sequencer and then I'm going to use read
to grab that input a number to store the
value in a variable called num right now
we have to make our first check and we
have to check whether the value is less
than 10 and the way we're going to do it
is we're gonna first use a pair of
brackets right and within the brackets
we're gonna type in dollar num - LT
space 10 and we have to put a space
immediately after the opening square
bracket and also immediately before the
closing square bracket right and LT here
stands for less than so what this thing
is going to do is it's going to check
whether the value stored in the variable
num is less than 10 okay and if the
value is going to be less than 10 then
we're going to display a message right
so we're gonna
put the keyword if there and on the next
line we put the keyword then and we will
display a message what do I write ah
maybe that was under the belt partner
that's cool enough on the next line we
now have to check whether the value that
has been entered is greater than twenty
right so obviously we're going to use
another pair of brackets and within the
brackets we're going to type in dollar
num space - GD this time and G d stands
for greater than space money and then a
space after twenty and a space before
dollar numb right now this is the second
check that we are doing in our script
but this is not the final check right
because the final check is to see
whether the number is between ten and
twenty or not so since this is an
intermediate check between the if block
in the s block we cannot use the keyword
else here instead we would have to use
the keyword eel F and eel if you can
think of it as a combination of s and F
and you always place your eel F blocks
between your if blocks and your s block
so if you have to make more than a
couple of checks in your script then you
would have to use a eel if blocks
between the if block in the s block
right and it works pretty much the same
as f would so on the next line you have
to use the keyword then again and on the
next line we will display a message
using echo that the value is greater
than 20 or maybe something happy like
that went over my head that's cool
enough on the next line we have to enter
our else block that's why I put the
keyword else there and we simply have to
display a message now that the value is
between 10 and 20 so instead of writing
that we type in something like now
you are making sets there you go our
shell script is almost ready now it's
just that I have to close my if lock by
putting the keyword Fi
so I'll save the script and I'll bring
up my terminal and I'll execute it and
the shell asked me for a number so I'm
going to put in fight first so when I
input five it tells me that that was
under the bed right I'll execute it
again and this time I'll put in 25 and
it tells me that that went over my head
okay and I'll executed once again and
this time I'll type in 15 and now it
tells me that I'm making some sense
right so I'll take you guys through the
shell script once again first we ask the
user to enter a number between 10 and 20
and then we store it in the variable num
and then we checked whether the number
was less than 10 by using the - LT
operator and by putting the entire
condition within square brackets and
remember you have to put a space
immediately before your square bracket
and also immediately after your opening
square bracket right and then we got
into the else sort of the if block and
we use the echo statement to display a
message that the value was less than 10
right next we made another check to see
if the value was greater than 20 or not
and this time we use the operator - GT
right and then we got into the e live
blog and we used echo to display another
message and if the number was not less
than 10 and if it was also not less than
20 then we would get into the else block
to display that the number was indeed
between 10 and 20 and that's why the
user was making sense to our script
right so in this script we have used two
operators the - LT operator and the GD
operator right LT stands for less than
and G d stands for greater than but
these are not the only two operators you
have at your disposal if you want to run
inequality check then you can use a EQ
right so - EQ would check if the number
dollar num is equal to ten or not right
and if you want to see if
number is less than equal to dollar ten
then you would have to use a le and if
you wanted to check if it was greater
than equal to ten and you would have to
use - GE and if you wanted to check
where the number was not equal to dollar
ten then you would have to use a - any
how obvious is that so I'm not going to
execute the script with these
modifications and said I would suggest
you guys to create a random shell script
and play with these operators and see
how they work and these are really easy
to remember as you must have noticed so
that's it for now that's all I wanted to
discuss in this tutorial and in the next
tutorial we're again going to discuss
something interesting so stick with me
thank you so much for watching this
tutorial and please subscribe to my
channel