Shell Scripting Tutorial for Beginners 5 - If Statement ( If then ; If then else; If elif else) Video Lecture | Complete Linux Course: Become a Linux Professional - Software Development

hello guys there will be the next video
on shell scripting tutorial for
beginners in this video we will see how
we can use the if statement in our
script now if you are familiar with any
other programming language you may know
that if statement can be used to
evaluate some condition and if the
condition is true then your you know
code will be executed otherwise it goes
into else condition or it's not executed
right so let's see how we can use if
statement in our bash script so to use
if statement in bash script you have the
basic skeleton like this so you write if
and then in square bracket you write
some conditional expression okay so I'm
going to just write here condition and
then you write a keyword called then and
then you if the condition is true then
you perform that statement and then if
the if statement is you know done then
you write fi for the end of this
statement right so this is the basic
syntax of if statement let's see how we
can use it with some example what I'm
going to do is I'm going to declare our
variable let's say the variable name is
count here okay and the value of count
is four examples 10 okay and we want to
evaluate this variable so what I'm going
to do here is in the square bracket I'm
going to just write the name of my
variable and then there are some
comparison operator here I can use with
the integer so for comparison what you
can use you can use equality or non
equality or greater than or less than or
greater than and equal to or less than
equal to right so
these are the comparison operator you
can use so I'm going to show you the
list which are the operator you can use
with integer so you can see this is the
list I have so you can use with integer
- EQ 4 equal to minus n e4 not equal to
then GT for greater than GE for greater
than or equal to LP for less than and le
for less than or equal to and if you
want to use these angle brackets then
you need to use doubles parentheses
instead of this kind of square bracket
so let's use our first comparison
operator which is equal to right so
after this count you just need to write
EQ for equality and let's compare it
with for example nine right which we
know that this condition is not true
because 10 is not equal to 9 right so
what we can do here is we can echo that
this condition is true or false right in
our case this is not true so nothing
will be printed right so let's run our
code and let's see what happened so I'm
going to run our script and prints
nothing because 10 is not equal to 9
right but if I just use 10 here which is
the true condition then let's see what
happened so it print condition is true
right in a same way we can use all these
expressions which I have shown you so
for example ne4 not non equality so any
and let's use the 9 here which is a true
condition because 10 is not equal to and
9 right and once again going to show us
condition is true okay
and so on so if you want to use greater
than just write GT here GT so 10 is
greater than 9 which is true and you
will be able to see the result once
again right so all these operators you
can use to evaluate your condition in
the case of integer let's see this angle
bracket case also so for checking
whether this count variable is greater
than 9 or not we can just use this kind
of angle bracket and wherever the angle
bracket opens it has to be a bigger
number in order to fulfill the condition
so let's see what what is the result of
this script and it feels true and if you
want to just run it with double parent
this is also this expression you can
just use it double parenthesis and then
run it then it says true also right so
this kind of expression you generally
use with double parenthesis right and
you have other expressions also like
greater than or equal to or less than or
equal to so let's see this expression
this is also true condition so you will
see your you know result here now for
comparing the strings you have to use
for equality single equal to or double
equal to they are same and if in the
case of non equality you can use this
kind of exclamation marks and equal
symbol or you have the angle bracket for
you know checking the alphabetical order
okay so let's say our for example we
have the word and let's say it's ABC
right and here we can just use the
square bracket once again and then we
can just write in the name of our
variable which is word
and then to check whether it's equal to
whatever we are providing here so for
example we say ABC let's check whether
this condition is true or not right so
let's run the script and sales condition
is true now let's change this comparison
for example some random keyword and you
can see there is no result
that means this string is not equal to
the string which is in the board of
variable right so for string comparison
you use single equal to single equal to
will also work here so for example I
have this and single equals and then I
run the script once again it says true
so you can use for equality single equal
or double equal which is they do a
little bit weird when you compare it
with some other languages for example C
or C++ or Java or any other language
they use this double equals for equality
but in our case you can use single
equals or W column script right now you
can also use not equality or non
equality for string like this so for
example I have this string and this
condition is also true so whenever we
run the script
it says condition is true okay and
whenever you want to you know check the
alphabetical order then also you can use
at these angle brackets so let's say
this is a and here we have the B right
and let's run the script once again
let's say what happens so it says no
such file or directory so as we have
seen in the case of for integers
whenever you use these angle bracket you
need to use double parenthesis right so
whenever you use angle bracket with
strings
you need to use double square brackets
that's why you see this error here which
says no such file or directory right so
you just need to use double square
bracket with good string
whenever you use this these kind of
angled brackets right and let's run the
script once again and this time
hopefully it will run so it runs so keep
these you know conditions in mind so
whenever you want to use the comparison
operator with integers you can use
single square brackets which gives EQ on
any on GT operations whenever you want
to use these angle brackets on integer
comparison you need to use the double
parenthesis whenever you want to compare
strings you can use single equal to or
double equal to for equality and
whenever you want to use angle bracket
with strings you just need to use double
square brackets okay now there can be
some other conditions with if you can
use else condition also with if so let's
see how we can use as condition so you
may have guessed you just need to write
else here so just write else and then
you can just say for example condition
is false so if you want to use this kind
of expression you already may have
guessed that if the condition is true
then it is going to go to this block
after then before else and if the
condition is false then it's going to go
to the else statement and whatever is
written between s and the end of the if
or condition that code will be executed
right so let's run the code once again
and let's say we say that a is equal to
B which is false so else condition will
be executed right so it says condition
is false so if the condition is not true
then the L
statement code will be executed right
now there is another way you can use FL
condition so if you want to evaluate
multiple condition and on the base look
for those multiple conditions you want
to execute your code then you can use
if/elif/else condition so for example
I'm checking here if the variable is a
or not so for example I can here also
write if and then if the condition is
true this statement will be executed
otherwise I can also write here else if
condition so just write L if and inside
LF once again write them and then here
you can also write some statements so
for example you can just write something
like this so whenever this condition is
true we will print condition for example
B is true here and then here we will
write condition a is true and here we
need to write some one again some
condition to check so with LF also you
can use these kind of conditions and
then for example we will just say a here
right because we are searching for a
word is a and this will be acquainted
right so once again run the script and
let's see what is the result is and you
can see condition a is true which is
this one because our word variable is
equal to a which is this condition right
so if this condition is false then this
condition will be evaluated and if it's
true then this code will be you know
executed otherwise the last option is
this option in else condition so in this
way you can use if-else condition if
condition and LF condition in your
script so I hope you've enjoyed this
video please recommend subscribe and bye