Shell Scripting Tutorial for Beginners 15 - WHILE Loops Video Lecture | Complete Linux Course: Become a Linux Professional - Software Development

hey guys back up to the next video on
shell scripting tutorials for beginners
and from this video I will show you how
you can use loops in shell scripting and
we will start with while loops so first
of all what are loops the loop's are
used to execute a list of command
repeatedly so if you want to execute a
command or list of commands repeatedly
you can use loops so let's see how we
can use while loop and first of all we
will see what is the syntax of while
loop so the syntax of while loop looks
like this so you use the keyword while
and in the square bracket you give the
condition which you want to evaluate and
if the condition is true then this
command which are in between the keyword
do and done are executed right so you
write the keyword do and then whatever
command you want to execute and when you
are done with the while loop then you
use the keyword done so let's take an
example and then we will see how we can
use loops so what I want is I want to
print the number 1 to 10 or using while
loop so I am going to declare a variable
n is equal to 1 so I am assigning the
value of 1 to n variable and then we
will evaluate a condition so what
condition we want to evaluate we want to
evaluate whether the value of n is less
than or equal to 10 or not and we have
seen this - le flag in the if conditions
also right now inside or in between do
and done keyword we can execute any come
on so what we are going to do is we are
going to use echo and then we are going
to print the value of n but still we are
not done because we are just printing
the value of N and the value of n is 1
right so it
execute infinitely because this
condition is always true right so we
want the code to increment the value of
n and then we are good to go so how we
can increase meant the value of n we can
just use n is equal to and then you can
just write dollar and double brackets
and then n plus 1 like this and then
this will increment the value of n by 1
and assign it to and once again right so
let's run the script once again and
let's see what happens and it prints the
value of N or it prints the number 1 to
10 right now what's happening in this
loop so we have initially assigned the
value of n is equal to 1 and then once
this while loop is reached this while
loop evaluates if the value of n is less
than or equal to 10 or not and first of
all the value of n is 1 which is less
than or equal to 10 which is true and
then it prints the value of n which is 1
so it prints 1 here and then increments
the value of n by 1 so now the value of
n becomes 2 and once again it will go at
the top and then here now the value of n
is 2 which is still less than or equal
to 10 so once again this code is
executed right and the 2 is printed
right in this way this will increment
the value of n until 10 is reached and
when the value of n is 10 this condition
is still mad because n is equal to 10
which is you know conforming to this
condition so it will print the value of
4 10 here and then once the value of n
becomes 11 and it reaches here so 11 is
not less than or equal to 10 so this
loop condition
is false at this time and then this code
will not be executed so once this new
condition is false the code will not be
executed right so this is what is
happening here now the incrementation of
variable and you can do in several ways
so you can do something like this or you
can just use the double bracket to
increment the value of n and you can use
double + which means post increment
right so once again when I run the
script it prints the value 1 to 10 once
again now you can also do pre increment
like this so just to pre increment and
once again and we'll run the script and
it prints the value of 10 once again 1
to 10 now in here instead of using these
square brackets you can also use these
double parenthesis as we have seen with
the if conditions also so this notation
will also work but instead of using this
- le flag you now need to use this kind
of angle bracket and is equal to right
so whenever you are using double
parenthesis you need to give this kind
of conditions right and then once again
when you run the script it per still
prints the value 1 to 10 right let me
clear the terminal and this is how you
can use while loops in bash scripting
now in the next video I'm going to show
you how you can for example read the
files using by loops and do some other
cool stuff with while loops so stay
tuned and please recommend subscribe and
bye for now