Shell Scripting Tutorial-19: Positional Parameters Video Lecture | Shell Scripting: Discovering to Automate Command-Line Tasks - Back-End Programming

hello guys my name is mother and welcome
to my channel this is the 19th tutorial
in the series of tutorials on UNIX shell
scripting now in the last year already
we learned to use variables in our shell
scripts now what we're going to do in
this tutorial is we're going to
experiment with variables in the
terminal we're not going to use the
shell script for that I'm just gonna
show you guys how you can play with your
variables and I particularly want to
stress on the fact that variables can
hold different kinds of values and you
don't have to mention the kind of values
that they can hold in your shell scripts
at all so what I mean by that is if
suppose I wish to create a variable
called a and if I want to assign it a
value say 25 which is a number if I
press the Enter key and if I then use
the echo statement and called my
variable a with the dollar symbol and
press Enter
I see that my value gets printed now if
suppose I wish to change the value of a
from 25 to a string then I can do that
and I don't have to remove my variable
and then create it again to do that I
can simply change the value by assigning
it a new value like hey what's up and of
course the string has to go inside
double quotes and when I press the Enter
key and echo my variable again then I
see the new value and what basically
happens is when you create a variable
and when you assign it a value even if
you use numbers in your value the shell
stores the variable as a string and if
you want the shell to use the numeric
value that the variable holds then you
have to tell it in advance and when we
check out commands like expr or BC for
mathematical expression evaluation at
that time we'll see how that's done but
for the time being just remember that if
you want to change the value of your
very own
then you can simply assign it the way
you assign it the first time so that was
it and now as in the last tutorial we're
going to create a script file and we're
gonna do something with it and this file
is let me first save it so that I get
syntax highlighting I'll call it ssj4
dot message now save it in my home
directory
and there you go and this file takes a
file name as an argument and renames it
yeah so that's what we're gonna do we're
gonna create a shell script that takes a
file name as an argument and renames it
right and the first thing that we're
gonna do in this file is we're gonna use
the MVP one because that is the command
that is used to rename files and then
we're going to use positional parameters
now what are positional parameters
positional parameters are basically
system variables that hold the values
that we provide at the time of running a
shell script that is when you type in
your SH command and then you type in the
file name the script that you are
executing anything that would follow the
script name would be the arguments of
the script and they would be stored in
system variables and what you get a hang
of it in just a moment I'll use dollar
one because dollar one is the first
positional parameter that is used and it
will basically hold the name of the file
that we provide as an argument to our
script and then we'll ask the user to
provide us the alternate name and you
know that can be stored in dollar two
and then we will basically display our
second file using cat so that's what
we're gonna do in this script and before
we execute it let me first create a
script for a source or a regular text
file and I'll call it test and I just
put in some text in it like this is a
test file and I see where it is in my
home folder it's right there and it'll
soon be renamed and I'll execute my
script file s s4 dot Sh
and I provide the name test as the first
argument and the second argument will be
the new name and this will be stored in
dollar one and the shell will use dollar
one as test and whatever will follow
will be stored in dollar too so wait
wait a second let me first executed in
short you guys call this file output and
when I press the Enter key I see that I
get the output of my test file but when
I run LS I see that I no longer have my
test file in my home directory but I
have a file called output so my file has
been successfully renamed now if suppose
I do not want to provide the second file
name in my as an argument but if suppose
I want to ask the user to provide the
second file name to me while the script
is executing then that's also possible
provide file name file name and then
read a
rename and then maybe I can do wait a
second and we can go from here we can
play somebody here
every dollar one space dollar name and
then cat daughter name I can save this
file let me first clear my terminal so
that we don't get confused with the
output and I don't have to provide
output is a file name this time but wait
a second we don't even have our file
test so I'm gonna use output as an
argument because I rename test to output
and provide a file name I'll call it
random when I press the Enter key
I see the output of random and when I
run LS I see that I no longer have
output but I have random as a file so
there you go I wasn't at my best at
explaining the concept of positional
parameters but I'll make up Fred trust
me on that I'm running out of time in
this tutorial but in the next tutorial
we're gonna continue our discussion on
positional parameters and we probably
prepared another shell script so thank
you so much for watching this tutorial
and I'll see you guys in the next one
and please subscribe to my channel