Shell Scripting Tutorial-60: Create Your Own Commands Using Functions Video Lecture | Shell Scripting: Discovering to Automate Command-Line Tasks - Back-End Programming

hello guys my name is Marvin welcome to
my channel this is the 60th tutorial in
the series of tutorials on UNIX shell
scripting and this one is probably going
to be the most interesting tutorial in
this course and that's because we are
going to talk about functions and how
amazing they can be for us so I have my
text editor here and I've saved this
file in the home folder
it's called func and has the extension
SH and what do you have to create a
function it's actually pretty simple you
just type in its name so the first one
that I'm going to create in this script
is a YouTube and then you have to type
in a pair of parents right and once
you've done that on the next line you
type in the opening brace character and
then you can type in a bunch of c'mon
names right and I'm just going to use a
echo display a message on screen good
morning
that's it short and simple and then I'll
type in the closing curly brace
character right and the next function
that I'm going to create in the script
is by by right and the approach is going
to be the same but the command that I'm
going to put in its body is going to be
dad and then you put the closing curly
brace and I save this file and we won't
be executing this script in the same way
as we have been executing scripts in the
previous tutorials and there's a reason
for that the reason is that when you use
SH to execute a script the shell invokes
a sub shell and then it executes the
script right and the functions are
variables that you know are declared by
the script are not accessible from the
shell that has invoked the sub shell
right so we won't be able to access
YouTube or by by you know from the shell
if you use SH to execute the script so
if this is getting confusing for you
just you know take my word for it SH if
you use it then you won't be able to
access these functions so there is
fortunately a way around this problem
and we have to first make this script
executable and for that I'm going to
chmod so I type in chmod and then hold
up the space and then I type in the
addition symbol and then I type in the
alphabet X and X here represents the
permission to execute the script as a
program
and then I'll type in the name of my
file which is funk or Sh and when I
press the Enter key my script is now an
executable program right and then I can
execute the script by force typing in a
dot and then I'll give a space and then
type in the name of my file and the
space between the dot or the period and
the name of the file is pretty important
right so please make a note of that and
when I press the Enter key
my functions have been you know stored
in the shells memory so in order to
access them I just have to type in their
names so if I type in YouTube and press
the Enter key I see the message good
morning and when I type in bye-bye and
press the Enter key
I see the system's calendar so you know
I find this pretty cool and it's because
you know with functions you can create
commands you know and you can give them
your own names right you know if you
want to have a command that has the name
of your pet then you can do that using
functions right and if you do not like
the name of a particular command for
example if you do not like cat to view
the calendar or date to be the system's
date then you know obviously you can use
functions and create your own commands
and you can actually do pretty
sophisticated things I've chosen these
two really simple functions you know so
that you know I can get across the
message to you how powerful functions
can be and how easy it is to create
functions and use them right and if you
want to remove a function from shells
memory then that's pretty simple as well
all you have to do is type in unset and
then give a space and type in the name
of the function that you wish to remove
so if I want to remove YouTube and you
know I can type in unset space UT then
press the Enter key and now if I would
try to you know execute YouTube I would
see the message command not found so
that's an error message right so I hope
you guys had fun watching this tutorial
I'll see you guys in the next one in
which we will discuss how to execute one
script within another script and that
one is probably going to be the last
tutorial in this course and I'm really
excited about it so see you guys in the
next tutorial thank you so much for
watching this one and please subscribe
to my channel