Shell Scripting Tutorial-25 Math On Real Numbers Video Lecture - Shell

hello guys my name is mother and welcome
to my channel this is the 25th tutorial
in the series of tutorials on UNIX shell
programming now in this tutorial we're
gonna check check out how to perform
arithmetic operations on floats or real
numbers and / new numbers I mean numbers
like ten point five or fifty point three
- or any number that has a decimal point
and something on the right side and
something on the left side so I
discussed when I spoke about expr that
expr is capable of you know performing
such evaluation so we obviously have to
use another tool now what I'm gonna do
is I'm gonna create a shell script in
which will perform all these evaluations
call it SS 9 toward Sh I'll save it in
my home directory and I'll put a comment
something like floating point arithmetic
right and there's a type of there
doesn't really matter it's a comment but
still I don't like to have typos in my
sentences so what I'm gonna do first is
I'm gonna create two variables and the
first one is going to be called a and
I've given it a value 10.5 and the
second variable B can have any other
value something like 3.5 maybe right now
what I'm gonna do is I'm gonna do four
evaluations I'm gonna first add daughter
a two dollar B and then subtract
daughter be from daughter a and then
multiply the two variables and then
divide one by the other
so dollar a plus dollar B is going to be
the first expression you value eight and
then daughter a minus dollar B is going
to be the second one dollar at a
multiplied by dollar B is going to be
the third one and ordered a the padded
by it already know sorry daughter B is
going to be the last one now
multiplication symbol has special
meaning as I have
you guys and we would have to escape it
just as we did with eh PR right now I
said that we cannot use expr and we have
to use another program and this program
is called BC now BC works in a slightly
different way you know you can't use BC
with the simple reverse codes and then
echo the results out instead what we
would have to do this time is we would
have to echo these statements out first
and people have to feed the result of
the echo operation to BC so when I would
echo daughter a plus daughter B what
would happen is dollar a plus dollar B
would be redirected for output on my
screen right but I don't want it to go
to my screen instead I wanted to go to
BC which is the program that I'm gonna
use so I'd have to use the pipe symbol
now the pipe symbol you can get it by
pressing the shift key and then pressing
the backslash character the same
character that's between your backspace
in the Enter key right and then you have
to type in BC which is the name of the
program that we're going to use and I'll
explain this thing again just a second
let me first type in this
there you go so what I meant was when I
echo this thing then what would happen
is daughter a plus daughter be I mean if
I would if I would you know just do it
on the terminal if I would just type in
echo daughter $8 plus daughter B what
happens daughter a plus daughter B would
be printed or displayed on my screen
right now I not wanted to go to my
screen instead I wanted to be fed as
input as an expression for my program BC
so I would have to tell the shell to
somehow take this and give it to BC and
ostbc do you know I mean do the
evaluation and the way in which you do
that is by using pipe symbol and this
symbol is known as pipe symbol and I
told you how you can get it now this
entire thing is going to get get me my
results so daughter a plus or B is going
to be ten point five plus three point
five which is gonna be what 14
but how would I echo the result out we
haven't really done anything to echo the
result out yet right so what I'm gonna
do is I'm gonna first assign these
values or the outputs to variables and
then then and then I'll echo out the
variables one by one right so in order
to evaluate this entire expression I'll
have to put the expression in Reverse
quotes that's what I'm gonna do there
you go it really is as simple as that
and then I'll assign these outputs to
variables so I've used a and B already
so C would have to keep this D would
have to keep this you would have to keep
this result and F would have to keep
this result and now my work is 99.99%
done I just have to echo out my
variables c d e and f so echo dollar c
echo dollar d echo dollar e and echo
dollar f so there you go my script is
ready I'll first run it to you guys and
then do a recap there's my terminal I
search space
nine or message not press the Enter key
there are my outputs so ten point five
plus three point five is 14 so there you
go you have the addition and ten point
five minus three point five is seven so
you have the subtraction result there
and ten point five times 3.5 is 36.7 and
if you don't trust me or if you don't
trust unix then you can use a calculator
and what UNIX is gonna do the
calculation anyway but you know you can
still verify so ten point five times
oops nine point five times three point
five is thirty six point seven five and
that's why it's it is just you know I
mean displayed it to what one decimal
place so that's why it's thirty six
point seven and the last result was ten
point five divided by three point five
and you can use a calculation for that
to ten point five divided by three point
five is three so there you go you have
three on screen so now I'll do a brief
recap of what we did in this tutorial
firstly we have to do floating-point
arithmetic and I told you guys in the
last tutorial that we cannot use the x
squared we have to use BC now BC works
in a different way it doesn't work in
the same way as expr and what I've done
is I've echoed out the expressions that
I wish to evaluate right through the
echo statements and I felt I have fed
the output of my echo statements to BC
using the pipe symbol now this is new so
you know you can make an olefin and
after PC has evaluated these expressions
I have stored the outputs in variable C
D E and F and then I've echoed out those
values in the echo statement at the end
so there you go I hope you guys have
understood and it really is a simple
concept it's just that I've discussed a
lot of things in one tutorial I've
discussed BC not discussed pipe symbols
and I both we use reverse quotes but I'm
sure you guys are capable of handling
much more complicated stuff this is
probably kids stuff for you guys so
thank you so much for watching this
tutorial as
you guys in the next one in which we
will discuss something interesting again
please subscribe to my channel and I'll
see you soon