Shell Scripting Tutorial-34: The 'AND' Logical Operator 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 34th tutorial
in the series of tutorials on UNIX shell
programming in this tutorial we're going
to begin our discussion on logical
operators and there are three logical
operators that UNIX provides us the and
operator the or operator and the not
operator the not operator we've already
met once before and that was in the
previous tutorial if you remember when
we discussed how to check whether a
string was not equal to another string I
told you guys to use the exclamation
mark and the equal to sign has the
operator now the exclamation symbol in
the operator is actually the nod
operator and what it does is it reverses
the evaluation of a test so if a
statement was going to evaluate to true
then it would then evaluate to pause if
you would place an order greater before
it right and vice-versa
maybe in the future I'll record a
tutorial in which I will discuss the nor
operator again but for the time being I
just want to concentrate on an or so
what I'm going to do is I'm going to
create a shell script that demonstrates
the and operator and I have my text
editor up here and I have saved this
file in my home folder given it the name
and dot SH and what this script is going
to do is it's going to ask the user to
enter a number between 1500 right and
then it's going to store the input in a
variable and then it will check using
the test statement whether the input
that has been provided is indeed between
50 100 or not and it's going to do that
by running two tests the first test is
going to check whether the number is
less than 100 and if it is less than
hundred then it's going to check whether
the test of whether the number is
greater than 50 or not and only if both
the tests would evaluate to true we
would print a message like the user is
within limits and if any one of those
tests evaluates to false then we would
print a different message right so it's
going to be a very simple
straightforward script but it's going to
explain to us how the and operator works
so what I'm going to do is I'll use the
echo statement to ask the user to enter
a number between 1500
and on the next line I'm going to use a
reed to store the input in the variable
num and now we have to check the value
of nama and we have to first check
whether num is less than equal to 100
and then we also have to check whether
num is greater than equal to 50 now
these are the two tests that we wish to
execute but we can't just uh you know I
mean put these tests within the square
brackets like this what we have to do is
we have to instruct the shell how it has
to go about conducting these tests that
is a you know if we are interested in
you know just the evaluation of this
test or just the evaluation of this test
or if we wish to you know have both
these tests run and have both these
tests returned and exit status of zero
you know I mean based on what we want we
will choose our operator and since in
this case we want both these tests to
return a true value we are going to use
the and operator and it's a symbol is a
- a and that's what you have to place to
use the + operator and I'm gonna put
this entire test in the if statement and
we would only enter the if block if both
these tests would evaluate to true so
this and this both should evaluate to
true for us to get inside the if block
right now use echo to display a message
you are within limits right and if if
any one of these tests evaluates to
false then we're going to display
another message using echo of course you
are out or limits
right and then of course we would have
to close our if lock by using the
keyword fi I'll bring up my terminal now
and I'll execute the shell script using
SH and thought SH which is the name of
my script file and if I enter 45 then it
tells me that I'm out of my limits and
if I enter 125 then again it tells me
that I'm out of my limits because 45 is
less than 50 125 is greater than hundred
but if I input a number between 50 and
hundred something like 89 then it tells
me that I'm within my limit so through
the shell script what I wanted to tell
you guys was that if you want to run
more than one test on strings or numbers
or own files at the same time then you
have to use a one or more conjunction
operators to instruct the shell how you
want to go about executing those tests
right so in this case since we wanted
both these tests to return and exit
status values zero or if you wanted both
these conditions to value to true we use
the and operator right if we wanted any
one of these tests to evaluate to true
and you know we didn't really care for
example if dollar numbers less than
hundred then you know it didn't really
matter to us where the dollar number was
greater than fifty or not if that was
the case then we would have used a
different operator but since in this
case we wanted both these conditions to
be true that's why we've used the and
operator so I hope you guys have got the
message and this is the first logical
operator and in the next tutorial we're
going to learn how to use the or
operator in our scripts so thank you so
much for watching this tutorial I'll see
you guys in the next one please
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