Shell Scripting Tutorial for Beginners 13 - The case statement Example Video Lecture | Complete Linux Course: Become a Linux Professional - Software Development

hey guys welcome to the next video on
shell scripting tools for beginners in
the last video we have seen how we can
use the case statement in shell
scripting now in this video we will take
one more example on case statements and
we will consolidate our knowledge which
we have gained in the last video so we
already know that how case statement
works in scripting and this is the basic
syntax which we have learned in the last
video so let's take an example and this
time we are going to use some pattern to
evaluate some cases so let's say we want
to allow the user to enter any character
and then we will evaluate that character
and based upon the character entered by
the user we will display if it's a
capital letter or a small letter or a
integer or some other special character
or it's not a character he entered some
string for example so let's get started
so what I am going to do is on the top I
am going to ask the user to enter some
character so I will just use - II for
this and I will say enter some character
and then we will allow the user to enter
the character on the same line right and
then we will take that character using
the read command so just write read and
then we will save it for example in a
value so just try it value variable and
then we will take this variable so I am
going to remove this variable because we
don't need this variable so now our
character or whatever input is entered
by the user is in the value variable so
we will evaluate this value expression
and then we will check if it's a capital
letter or small letter right
for that we can use some patterns now
how pattern works so for example we want
to evaluate if user has entered the
small letter A to Z so we can may use
this square bracket and then you just
need to write a and then minus Z and
this pattern represent that we are
expecting a small letter between A to Z
okay in a similar way if you want to
evaluate a capital character then we can
just say capital A to Z like this so
this is the pattern for capital A to Z
right now if you want to evaluate the
number any integer 0 to 9 so we can just
write 0 to 9 right now if the user
enters any other special character for
example Asterix or some other characters
which is not the part of e to Z or any
number then we can evaluate it with the
question mark now what is question mark
question mark is a pattern which expects
any special character any character
which is one letter character right and
this asterisk or star symbol R waits for
more than one character so it can be one
on more than one special character so if
the user enters for example any string
and not a character then it goes into
this situation or in this case and this
is for only one character any special
character right and here we can echo
that character so for example user
entered value and then we can just say A
to Z smaller letters write in a similar
way for capital A to Z
can just right here capital a to Zed and
in the case of integer let's copy this
and paste it here and we will just say 0
to 9 and in the case of question mark we
will just say it's a special character
right and in the last case we will just
say unknown input so we will just write
here unknown input so let's run the
script and let's see what happens when
we run this script let's run the script
and let's enter any small letter for
example app and then press Enter and say
the user entered letter F which is
between small a to small Z right once
again let's run the script and this time
we will enter the capital K for example
and then press Enter and you can you see
there is an error here because we were
expecting this statement to be printed
which is capital a to capital Z but here
it prints user entered capital K but
then it prints small a to Z so it goes
into this condition and if you also get
the same error then most probably you
need to do a small hack and this is you
just need to set the Lang as C so just
write Lang is equal to C so in capital
Lang is equal to capital C and this
means you are setting a languor
environment variable is equal to C right
and this means that you are using the
safe locale everywhere in your operating
system so if it doesn't work for you for
capital letter the script you just need
to set this environment variable as C so
lang is equal to C and once again we
will run the script
and once again we will enter the capital
K and this time it shows the right
result to us right so if you face the
same problem just use this environment
variable is equal to C right once again
let's run the script and this time we
will enter any number and press ENTER
and says of course it's between zero to
nine right or any other number for
example five it's also between zero to
nine right now let's enter any special
character so I'm entering for example
this and symbol which is a special
character and then press Enter
and it says user entered this and it's a
special character now let's enter any
random string and let's see what's the
result so it says unknown input right so
in this way you can match characters
using these kind of patterns right for
more information on patterns and regular
expression you can always search for a
regular expression and you will see a
vicky pedia page on regular expression
and you will be able to understand and
read their what the square bracket is
what is - what is this question mark
stands for or what is this asterisk
everything so the Wikipedia page for
regular expression has a good
explanation on pattern so just read that
Wikipedia page and you will be able to
understand these patterns in a better
manner so case is not just used for our
strict letters or characters you can you
know evaluate any patterns using the
case statement and that's the beauty of
this case statement so I hope you
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