Shell Scripting Tutorial-38: Another Date With 'case' Statement 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 38 tutorial in
the series of tutorials on UNIX shell
programming now in the last tutorial we
checked out the case statement and to be
honest I wasn't satisfied with my own
performance of explaining the statement
to you so what I'm going to do is in
this tutorial I'm going to take up
another application of case and I'm
gonna try to do a better job of
explaining the statement to you so I
bring up my text editor here and I've
already saved this file in my home
folder given it the name word and the
extension SH and what this script is
going to do is it's going to ask the
user to enter a word and then using read
we will store that input in a variable
that's that we're going to call word in
the script and then we will check
whether the word begins with a lowercase
or an uppercase waffle that's going to
be our first case the second case is
going to be to check if the word begins
with a digit and the third case is going
to be to check if the word ends with a
digit and the fourth case is going to be
to check if the word is a three-letter
word or not and the last case is going
to be the default case which will get
executed if all these cases fail and
that's going to just display a stupid
message right so the script is going to
be pretty simple and I've chosen this
example because it's going to introduce
a couple of meta characters to you and
you know it's also going to deal with
case in a better way so let's get
started
on the first line I'll type in echo to
display a message enter a word and this
is because the user should know what is
expected of him the next line we use
read to store the input in the variable
wor D that's word and then we have to
begin our case and I'll type in the
keyword CAS C and then the control
variable which in this case is going to
be word so dollar word since we are
interested in the value and then the
keyword I in and then we are going to
type in our case conditions and the
first case as I mentioned is going to be
for lower case and upper case vocals so
AE IO and you this is the range for
lower case workers and since which we
are going to check whether the word
begin
to the wall or not it's just the first
character diet has to be in this range
for this case to get executed right so
for all the other characters since we
don't really care I'm just going to put
an asterisk right so if the first letter
lies in this range pretty good we don't
really care about the rest of the
characters that's why there's an
asterisk here but I'm not going to make
a separate case for uppercase vowels
instead I'm going to use the pipe symbol
here and what the pipe symbol is going
to do is it's going to ask the shell
wait a second let me type in uppercase
water AE I own you and of course the
asterisk symbol yeah so what the pipe
symbol is going to do is it's going to
instruct the shell to check if the first
alphabet in word lies in this range and
if it doesn't lie in this range then it
will ask the shell to not skip the case
but to check whether the letter lies in
this range right so both ranges will be
covered in a single case and that's why
we've used the pipe symbol in between
and then again the syntax says that we
have to put a closing parent here so
that's what I'm going to do and it's
there now and on the next statement I'm
gonna on the next line so I'm going to
use echo to display a message like the
word begins with bubble right and to
terminate the case I'm going to put two
semicolons right and now the next case
is going to check if the word begins
with a digit or not and I'm going to use
the square brackets metacharacters again
and the range of digits is of course
from zero to nine so I'm going to type
in zero and then a - and then the digit
nine and the closing parents oh sorry we
have to again put an asterisk here
because again we are testing to see if
the word begins with the digit or not
right so the first factor in the in the
input will be matched with the digit
between zero and nine and if a match is
found then this case will be executed
so on the next line I'm gonna use echo
display a message the word begins with
digit right and of course the two summer
cones to end the case and on the next
line we're going to write the test
condition for the third case and that's
going to be to check if the word ends
with the digit or not so instead of
typing in the range first and then the
asterisk symbol what I'm going to do in
this case is I'm going to type the
astrick symbol first and then I'm gonna
type in the range which is going to be 0
tonight so what will happen is the shell
will see that okay there's an asterisk
in the test condition so you know maybe
I just have to ignore a few characters
and as it reaches the square bracket
here it will see that okay you know
maybe I have to just match the last
character and how do I have to match it
with what do I have to match it I have
to match it with the range that's
represented by 0 - 9 right so if you put
an asterisk in a before the range then
the first characters are ignored and
just the last actor is matched and if
you put the asterisk symbol after the
range then the first character is
matched and the last characters or the
characters that follow are ignored right
so I'm gonna put the closing parent to
get inside the case and then I'll use
echo to display a message like the word
ends with DJ so to terminate this case
I'm going to use a few semicolons and on
the next line I'm gonna type in the
condition for my fourth case and that's
going to be check if the word is a
three-letter word or not and three
letter words can be thought of as you
know combinations of three characters
and one character as I mentioned the
previous tutorial can be represented by
a question mark so for a three-letter
word we can use three question marks and
that's going to be our test condition
right so three question marks and the
closing pattern
and on the next line I'll use echo
display a message you entered a
three-letter word that's great and of
course I'll have to terminate this case
by typing in my two semicolons and
lastly I'm gonna type in the asterisk
symbol and the closing parent and this
is going to represent the default case
and this case will get executed only if
the above for case is a fail stupid
statement something like I don't know
what you have entered so the two
semicolons are indicate the termination
of this case and now since all our cases
have been written and the code for all
the cases has been written as well what
we have to do is we have to terminate
the entire case block and the way we do
that is by typing in the keyword case
but this time in the reverse way so in
DES AC right and I save this file okay
everything seems to be correct so I'll
bring up my terminal now and execute the
script SH space word dot Sh that's the
program so it asks me for the word so if
I type in something like Apple right
Apple begins with the a and uppercase a
that is in this case and a is a vowel so
it should display that a message like
you entered a vocal the word begins with
a vowel gap so that's the span correct
output now if I type in something like
Baal then it tells me that I don't know
what you've entered because there is no
case in our script that is prepared to
match with such an input but if I type
in a word that begins with a digit like
five Hadi
and if I press the Enter key then it
tells me that the word begins with the
digit type in Fahrenheit 451 then it
tells me that the word ends with a digit
with this is this case in this case it's
not really a word it's a it's a string
but even if you would type in a word
that ends with the digit display the
same message to you and if I type in a
three-letter word sorry something like
aa cat then it tells me that it's a
three-letter word and you can check it
once again for dog again it tells me
that it's a three-letter word so again
I'll walk you guys through the script
once more we have our case statement on
the third line and the control variable
is a dollar word and this is the input
that we've received from the user in the
script and once we get inside the case
block we have five cases the last one is
the default case which just displays a
message I don't know what you've entered
and it will get executed only if the
four cases that appeared before it
failed to execute and why would that
happen it would happen only if the first
letter in the input is neither a
lowercase bubble or an uppercase bubble
or if the first letter is not a digit
and also if the last letter of the word
is not a digit and also if the word is
not a three-letter word so I hope you've
got the essence of case in this tutorial
in case you missed it in the previous
tutorial and if you think that I still
haven't made it clear for you and please
stick with me in this tutorial I'm sure
we will encounter case multiple times
sorry in this course and maybe in future
I will clarify things for you in a
better way so thank you so much for
watching this one and I hope to see you
guys in the next tutorial please
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