Shell Scripting Tutorial for Beginners 23 - Functions 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 and some of the next
coming videos I am going to show you how
functions works in shell scripting so
let's get started
so like any other programming language
bash also supports function though they
have somewhat limited implementations
right now first of all what is a
function a function is a subroutine or
you can say it's a code block that
implements a set of operations so for
any user it's like a black box right it
has some name and it implements some
functionality and then later user can
use this function once or multiple times
so let's see an example and let's see
how we can use functions in shell
scripting so there are two ways of using
functions one is like this and this is
the first look at notation and for this
you use a keyword function and then you
give a name to your function and then
you execute some commands right the
second notation for the function is like
this so you directly give the name to
your function and then you give these
parentheses and then you use these curly
brackets and here comes your commands
right so like this or like this so you
can use functions like this in this
notation or in this notation okay so we
are going to see both of the notations
and we will see how we can use it so
let's say we want to print hello world
using a function right so let's do it
with this one we can just say hello here
or you can add say anything using
function right so you can give any name
to a function and then we can you know
give some commands inside this function
inside these curly brackets so I'm going
to just give echo and I am going to say
hello here right and in the next
function for example I want a function
that whenever I call it it's going to
quit the script right so let's say this
function name is quit okay and what it
does is it just calls this command which
is going to exit our shell script right
so let's use this function first of all
this Hello function to print something
so to use a function in a script you
just call it okay so let's first run the
script we have just declared these two
functions right and whenever we run the
script what happens nothing happens
because we haven't called any function
by its name so to call a function this
is just the declaration of a function
right so to call a function you just
need to give the name of this function
so for example I'm calling the function
hello then I'm going to run the script
is going to print hello right now let's
call this function which is a quit
function and I'm calling this quit
function before hello function right and
then let's say I'm just echoing
something so I'm echoing for example
some word whoo-hoo okay so let's run the
script and let's see what happens so I'm
going to just run the script and nothing
happens because what we have done here
is we have called a quit function first
of all and quit function just creates
the script and the chance of calling
this or this does not come because this
function is called first and it directly
quits
the script right let's see the sequence
like this so first of all we call holo
and then we call this squid function
after the holo function and let's run
the script and now holo is printed but
this echo is not printed echo Fuu right
because the sequence is something like
this so first holo function is called
and this is printed and then we call the
squid so the script is exited and the
chance of printing this does not come
right then let's use this quit after the
echo command and then once we run the
script it prints hello from this
function and then it prints fool from
this command and then we call the quit
function which exits the script
okay so sequence of calling the function
is important right so however you call
the function in whatever sequence it
will be called in that sequence so first
of all we are calling the hello here
then hello will be called and if you
call you know quit at the top then quit
will be called first and then the other
function right so sequence is important
and the function declaration can be done
in any sequence right declaration can be
done in any sequence but what matters is
the calling of the function so on in
whatever sequence you will call the
function they will be called in that
sequence right now second thing is how
we can pass any argument to a function
so there are some ways of passing some
argument to our function and let's see
how we can do it so call this function I
have declared hello here right instead
of hello I can just call for example
print this is a print function right and
then how it takes an argument or the
argument can be used in the with the
dollar symbol and then the number okay
so one means the first argument then if
we write 2 here then it means the second
argument and then we write 3 here then
it it means the third arguments for
example dollar two is the second
argument dollar 3 is the third argument
and so on right so what we want now is
what we want now is we want to call this
print function right so we can just call
this print function and how we can do or
give our an argument you can just give
the name whatever name or whatever
argument you want to give after the name
of the function so whenever you call
this function and give this argument it
goes here as the argument 1 + hello will
be printed so let's see what happens so
you can see a hollow will be printed and
then who is printed and then we quit the
application using this function now we
can call a function multiple times so we
can say hello world here and then you
can see it prints hello
and then world and then foo right so you
can call it multiple times so hello
world and then we can say again here
right and then we run the script I says
hello world again so you can call a
function with multiple times with
multiple arguments right and you can
call the function in sequence ok let's
give some other arguments here so you
can give $2 to and then you can give
dollar creature right and instead of
calling it multiple times you can just
care
this world as a second argument and
again as a third argument and then I'm
going to just remove these callings and
then run the script for example and it
prints hello world again because we are
capturing these argument using are these
you know variables so variable one is
for first argument variable two is for
second argument and variable three is
for the third argument right so this is
the introduction to function function
have more functionality than this simple
operations and this we are going to see
in the next videos so I hope you've
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