Shell Scripting Tutorials-29: The 'if-then-else' 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 29th tutorial
in this series of tutorials on UNIX
shell scripting now in this tutorial
we're going to learn to use the if then
else statement what we gonna do is we
prepared the shell script in our
previous tutorial right and it uses the
if statement and what it does is it
checks the exit status of the move
command that I have here and if the exit
Sirus comes out to be 0 then the
statement at line 6 that is the only
executable statement between the then
keyword and the FI keyword gets executed
and if the exit series of this command
is 1 which means that if this command
fails to perform its operation
successfully then the script does
nothing now we're going to enhance this
script in this tutorial and what we're
going to do is we're gonna make it
display a message for us even if this
statement returns an exit status of 1
that is if the file could not be renamed
successfully so it's actually very
simple what I'm going to do first is I'm
gonna create a new shell script and I'll
save it in my home folder and I'll give
it the name if-then-else the extension
SH now save it and I simply copy and
paste the code from the script file to
my new script file I'm feeling too lazy
to type the same code again and I'll
edit the comment and now we have to make
it do what we wanted to do so what I'll
have to do is I have to first place the
else keyword within the if block or the
if block is anything and everything that
appears between the 10 keyword and the
FI keyword so if I remove my else block
sorry the else keyword we just have one
statement that is the statement at line
6 in our if block currently but it can
have as many statements as you want so
you know if I would put a clear here
then my if block would have 2 statements
instead of 1 right and if I put let's
say put a touch command that it could
have 3 statements
that's the if block but if I would put
else here then the if Lockwood gets
played and by that I mean anything
between the Dan keyword and the else
keyword would now be the if block and
everything between the else keyword and
the fi keyword would be the else clock
and the else flock would get executed
when the exit status of the move command
here would be one so it's actually it
actually works in the reverse way with
if if the exit status of this move
command is zero then the echo statement
at line six gets executed and what else
if the exit status of this command here
would be one then the else block would
get executed so in the else block in
this tutorial we're just going to put an
echo statement and we are going to
display a message something like the
file would not be renamed there you go
I'll put a full-stop make things tidy
now I'll bring up my terminal and
execute the script for you guys
I said space if then else dot SH and
it's gonna it is it's asking me for two
names and I'll just supply two random
names I'll make sure that the first name
that I supply is not a valid file name
so I simply type in random because I
know that this file doesn't exist and
second file name would be anything you
do maybe and if I press the Enter key
then first the shell returns an error
message that you know that got generated
because of the failure of the MV command
at line four and after displaying its
own error message it displays the error
message that we wanted the script to
display in case the exit status of move
was one so you people must be wondering
what's the use of putting this echo
statement here the shell is anyway going
to tell us you know that there was some
problem with the move command the
purpose behind this tutorial was not to
you know
prepare a script that displayed an error
message but the purpose was to take you
guys through the if block the else block
and how these blocks actually get
executed and in what conditions these
blocks get executed that is the if block
works when the exit status of the
command is zero and the else block works
on the exercise s is one so you know
instead of having an echo statement here
you can have anything else and you know
that part of code would be executed just
the way the echo statement has been
executed so there you go
this wasn't the best example that I
could have come up with I have planned
better for this tutorial but anyway I
hope you guys caught the main message
behind the script and behind this
tutorial in the next tutorial we're
going to learn another statement that
would allow us to make you know
decisions in our cell programs it's
again a variation of the if statement
and it would provide us a few more
options so I hope you guys had fun
watching this tutorial thank you so much
for watching and I'll see you guys in
the next tutorial please subscribe to my
channel