Shell Scripting Tutorial-36: The 'OR' 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 36 tutorial in
the series of tutorials on UNIX shell
programming now in this video we're
going to get back to a discussion on
logical operators and learn to use the
or operator in our shell scripts so what
I'm going to do is I have my text editor
here and I've already saved this file in
my home folder given it the name or and
the extension SH and what this script
file is going to do is it's going to ask
the user to enter character and then
check whether one character has been
input or more than one characters have
been input and if one character has been
input then it would check whether the
character is a while or if it is a
consonant and it would display
appropriate message in either case right
so it's going to be a simple script but
it's going to illustrate the concept of
or operators to us properly so that's
why I've chosen this example and to see
if the number of characters that have
been input is 1 or if the number is
greater than 1 we prepared a script file
in the previous tutorial and I'm going
to use that code so I'll simply copy it
and paste it in my new file and I'll
have to make a few modifications to this
code and the first thing I'm going to do
is I'm going to ask the user do you know
just stick to lowercase characters
because I'm gonna you know prepare this
script to handle just lowercase
characters I can you know prepared to
handle uppercase characters as well but
you know that would just increase the
complexity a tad bit and that's not what
I want right so I'm not gonna do that
and I'll take away the statement because
I don't want to just display a message
that a character has been entered
instead I want to do something
meaningful and that is to see if the
character is a wall or something else so
in order to test I have to obviously use
the square brackets and within the
square brackets I would have to check my
variable value for each of the walls
known that is a e i/o and you write so
we'll have to obviously write a AEIOU
you'll have to write in 5 test
conditions within
our square brackets and the first one is
going to be for a and the next one is
going to be for e the next one or I the
next one for O and the next one for you
so all five balls have been covered here
ae IO and you and since we want any one
of these cases to evaluate to true to
get inside the if log I'm going to use
the or operator or the - o symbol
between my tests - oh and - oh so okay
that seems correct to me and I'm gonna
make this an F statement so I'll put the
if keyword here right
and now I'll uh you know really explain
this to you what would happen is dollar
bar would be compared to the lowercase
alphabet a and if this case would
evaluate to true then all these cases
would not be considered and we would get
inside the if block right so basically
what the or operator does is it
instructs the shell to execute one or
more of the test conditions that have
been specified and if any of the test
conditions returned and exit status
value one or you know evaluate to true
then just get inside the if block or do
whatever you've been asked to do but you
know I mean if this would fail then it
would execute this test and if this
would pass then you know all the other
tests would not be considered but if
this would fail then it would get here
if this would fear that it would get
here and this would if if this test
would fail it would get here only if all
the previous tests have been failed and
if this test would also fail well in
that case we won't get inside the if dog
but we would get inside the else block
right so inside the if block we're not
going to do much we're just going to use
echo to display a simple message like
you entered a bubble and in the else
block will display another message using
echo of course and that would be you
didn't enter a poll right and I'll close
the inner if block by using the keyword
F I save the script file and let me
check okay seems correct to me so I'll
bring my terminal up and I'll execute
the script using SH or dot SH now
firstly if I would enter a bunch of
characters and press the Enter key that
it tells me invalid input and that's
because this condition here it has
failed and we have got inside the else
block right but if there's one character
something like L then it tells me that
it is in a wall because L indeed is in a
wall but let me clear the screen if I
would execute the script with the input
a then it would tell me that it is a
wall if I would execute it with E again
I is of all O is a ball and oops and U
is also evolved but if I would execute
the script with the input B and it would
tell me that it isn't about so there you
go I'm sure you people have got the
message behind the script and what it
intends to do and how it does it and
once again the or operator is different
from the and operator the and operator
requires all the test conditions to
evaluate to true whereas the or operator
requires any one of the test conditions
that have been mentioned in the square
brackets to value to true right so
that's the difference and both these
operators are very important and we will
be studying them in greater detail as we
move along in this course but for the
time being this is all the information
that you need and thank you so much for
watching this tutorial I'll see you guys
in the next one where we discuss
something interesting again thank you
again for watching and please subscribe
to my channel