Shell Scripting Tutorial for Beginners 19 - FOR loop Video Lecture | Complete Linux Course: Become a Linux Professional - Software Development

hey guys welcome to the next video on
shell scripting tutorial for beginners
in this video we will learn how to use
for loops in shell scripting now if all
loops are also used to loop over some
lists of values and then execute the
command in the loop now let's see first
of all what is the basic syntax of for
loop and then we will see some examples
so there are several syntaxes we can use
with carloads and i'm going to show you
some of them so these are some of the
basics in texas we can use in the paw
loop so the first syntax here is we use
the for keyword and then we declare a
variable and then we use the keyword in
once again and then we gave the list of
values it can be for example 1 2 3 4 5
or it can be in the list format which we
will see a little bit later when we will
see the examples right you can even give
the files as an input here right so
file1 file2 Oh file 3 and we can even
give some Linux or UNIX command here as
an input ok and then we have the do and
done keywords in between we execute some
commands right now the next way of using
the for loop is similar to as we have
seen in for example in C programming so
we use 3 expression in between these
brackets and the first expression can be
used to initialize the value second is
to compare or if the condition is
fulfilled we check this in the second
expression and in the third expression
for example we can increment the value
which we have declared in the first
expression right so this is the other
way of using for loops right so let's
take some examples to understand the for
loop in a better way so let's take the
most basic example so for example I want
to
I create some numbers and I want to
print them so I can just write the
numbers like this so whatever number I
want to you know iterate on I can just
give the numbers separated by the spaces
so for example I want to give five
numbers then I can give these five
numbers here one two three four five
right and in the do and done keyword in
between these two keywords I can echo
the numbers using the variable so I can
just use the dollar symbol here and
instead of variable I can declare any
variable for example I or any variable
name whatever you want to give yes for
example I use I here right and that's
where you'll be like in print from here
okay and let's run the script and let's
see how it works so I will run the
script and it prints the number one two
five pretty simple right
now in case of longer ranges for example
you want to iterate over hundreds of
values this method is not you know very
beautiful because you need to write
every number and then iterate over it
right so if you have bash version
greater than three then you can use this
kind of notation also so you can give
any range in between these curly
brackets so for example I want to
iterate over one to ten I can just write
one and then double dot and then ten
here and this means that we want to
iterate over the range of one to ten
okay and then once again let's run the
script and let's see what happens and
you can see the result is the printing
of one to ten numbers right so this is
how also you can give any range between
any numbers right now there is one more
way of using this range so this will
work f-from
one to ten so this is the starting value
and this is the ending value and then
you need to use two dots here now if you
add two more dots then you can give the
increment by which you want to increase
the value for example I want to increase
the value by two every time this range
is looped over then I can write to here
right so basically what this range means
is the first value here is the start
value then double dot and then second
value is the end value and then the
third value of the dot is the increment
we want to give so I want to give the
two increment right so let's run the
script once again and let's see what
happens and you can see it start with
one because our initial value is one and
then the value is incremented by two
whenever we loop over this for loop so
every time we loop we increment the
value by two right if you want the value
of starting from zero you can do that
also so let's run the script and now we
have the number zero two four six eight
there now also you can do this but
remember this kind of notation you can
use with the version more than 4.0 or
bash right now you may ask how we can
you know print or how we can know the
version of bash we are using this is
pretty simple so you can just echo this
by using a keyword called bash version
this is the keyword which you can use to
print the version of bash so once again
I run the script and I can see I have
the bash version 4.3 point 11 right so
this notation will work on my you know
bash script but if it's lesser than 4
then this notation may not work in your
case and if you
are using this notation then you need to
have minimum version three or more okay
so I have four point three so both of
the notation works with my bash script
now let's see the other way of using for
loop in scripting okay so instead of
this notation I told you we can use
these double bracket notation and in
between we can give three expressions
right so let's declare for example I and
initialize it with zero right
and then by semicolon we can separate
these command or expressions and then in
the next expression we will check
whether this value of I is less than
five or not and then we can increase the
value of I by one every time we loop
over this loop right so this is the
first expression in which we are
initializing the value of I with zero in
the second expression we are comparing
or evaluating this expression whether I
is less than five or not and then we are
incrementing the value of I as we do in
normal programming right so you already
know how to do is so let's clear the
terminal I'm going to clear the terminal
and run the script once again and you
can see it prints from zero to five
right because the value of I begins from
zero and it evaluates whether the value
is less than five and if the value is
equal to five or greater than five then
this will not be executed okay so this
is how also you can use the for loops
now in the next video I am going to show
you how we can use for loops with files
and commands so stay tuned and please
welcome and subscribe and bye for now