Shell Scripting Tutorial-33: Run Checks On Strings Video Lecture | Shell Scripting: Discovering to Automate Command-Line Tasks - Back-End Programming

hello guys my name is mater and welcome
to my channel this is the 33rd tutorial
in the series of tutorials on UNIX shell
scripting in this tutorial we're going
to learn to play with strings and what I
mean by that is we're gonna prepare a
shell script that's gonna have a few
string variables and then we learn to
compare those variables and what I mean
by that is that we're gonna learn to see
if the first string variable is the same
as the second string variable or if the
variables are different or if a variable
is a null variable that is if it's
length is 0 or if its length is greater
than 0 we're going to learn to do all
that and this is going to be a long
tutorial so I won't talk in waste time
instead I have my text editor here and
I've saved this file in my home folder
I've given it the name string - test on
the first line I'm gonna put a comment
string checks and on the third line I'm
gonna create a string variable I'm I'm
gonna give it the name STR 1 right I'll
use the equal to symbol and double
quotation marks to assign text to a and
I'm just gonna type in something hey you
and on the next line I'll create another
string variable I'll give it the name
STR to put the equal to symbol and
assign text to it again what's up
remember if you put a character within
double quotes then it doesn't have any
special significance to the shell so you
can basically use any character that you
have in your keyboard right as long as
the characters are within double quotes
please keep that in mind and on the next
line I'm gonna create a null variable
and that is I'm gonna put an equal to
symbol
immediately after the variable name and
I'm gonna press the Enter key right so
that's one way of creating a null
variable the other way is if you put
double quotation marks but don't put
anything within the double quotation
marks that would also create another
variable so there you go these are the
three variables we're gonna have in the
script and now I'm gonna run a check to
see if my first string is same as the
second string right
and the way I do that is by using square
brackets and within the square brackets
I'll have the test dollar STR one is
equal to dollar STR two and since these
are strings and since we want the shell
to treat them a strings we'd have to put
double quotes here as well okay and well
I'm not gonna put any code after it
right so if these two strings are same
then we would just want to know whether
they're straight same or not and that we
can do by viewing the exit status of
this test and to view the exit status
again I would have to echo out the
system variable dollar question mark on
screen and those of you who haven't
followed this course and those of you
who don't know what exit status is you
can watch one of my previous tutorials
in which I've discussed exist iris you
can find the tutorial in the playlist
alright and the next test that we're
gonna do is going to be to check if the
strings are different and again I'm
gonna put my first string within double
quotes STR one but this time instead of
using the equal to symbol I'm gonna use
the exclamation symbol first and then
the equal to symbol so this combination
stands for not equal to right and I'll
give a space and put the name of my
second variable which is STR two in
double quotes again and a space after
the second variable ends and space
before the first variable begins and
again I'll use a echo dollar question
mark to view the exit status okay the
next check is gonna be to see if the
length of any of the first two strings
is greater than zero or not and the way
I do that is by using the option hyphen
N and then my string which would again
go in double quotation marks and I'll
just use string one here you can use
string two as well right because both
are not known strings and again echo
dollar question mark to view the exit
star s and the last test in this script
is going to be to see if the final
string is a null string or not
taller str3 the option that you use
within your square brackets to check for
the length of the string to be 0 is - Z
okay so that's something you have to
keep in mind and again you the exit
status dollar question mine so I save
the script file and I'll bring up my
terminal and I'll execute it string -
test Thor Sh
now in case you've forgotten I'll remind
you again that if a test evaluates to
true that is if a check is executed and
if it is found to be successful then the
exit status is 0 and if it is found to
be unsuccessful or false then the exit
status is 1 right so let us first view
the output and then match the output
with the checks so the output is 1 0 0 0
and there are four tests in our script
file the first test is to see if the
first string is the same as the second
string well is it the first string is
heyyou the second string is what's up so
they're obviously different string right
so this had to be one or false so that
is what we have here we have one as the
first line in the output the second
check was to see if the strings are
different well of course they are
different so the test should evaluate to
true or the exit status would be 0 and
what is the exit Syrus it is indeed 0
right and what do we have is the third
test the third test is to see if the
length of string one is greater than 0
or not equal to 0 whatever and that is
of course true again so the exit status
had to be 0 and what is it it's indeed 0
right it's right here you guys can see
it and the last check is to check
whether the length of string 3 is 0 or
not and that again has to evaluate to
true so the final test gives us the
output 0 right so if I would make some
changes here such as if I would put STR
3 instead of STR 1 here then this test
would give us different output why
because it would check whether the
length of STR 3 is
better than zero or not and that is not
the case because STR threes and null
variables so this test would evaluate to
false and the third output instead of
being the zero would be one so let me
see if I have saved the file well of
course I have
so I'll execute the script again and now
you can see that the third row has one
instead of zero so there you go this was
a pretty dumb subscript it didn't do
anything meaningful but the purpose
behind making the show script was not to
entertain you guys or maybe that was but
you know it definitely wasn't to you
know do anything meaningful the purpose
was to make you guys familiar with
string checks and to discuss with you
guys how you can play with your strings
in your shell scripts and then you know
branch control or you know put the
string checks within if statements and
execute you know codes of your choice so
you know there are a lot of things you
can do with this knowledge so you know I
hope you guys had fun watching this
tutorial and in the next tutorial we'll
discuss something interesting again so
please stick with me in this course and
I hope to see you in the next tutorial
thank you so much for watching this one
and please subscribe my channel