Shell Scripting Tutorial-45: The Internal Field Separator 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 45th tutorial
in the series of tutorials on UNIX shell
scripting in this tutorial we're going
to talk about something called ifs now
ifs stands for internal field separator
before we check out what ifs is and what
its significance is what I'm going to do
is I'm going to take a minute and
refresh your memory about the set
command in case you've forgotten how it
works so I have my terminal here and
when I type in set and past wait as an
argument a string of text I'll just type
in something random like this is the
45th Dorian and when I press the Enter
key what set does for me is it sets the
positional parameters with the words in
the sentence so if I would echo out the
value of positional parameter dollar one
and you would see the first word in the
sentence which is this if I would echo
out the value of dollar two then you
would see the second word which is is
and if I would echo out the value of
dollar six then you would see the sixth
and the last word in the sentence which
is tutorial so how does Unix decide
which word has to be assigned to which
positional parameter it does so by
looking for the internal field separator
in the sentence and the default value of
the ifs is the space character or tab or
even newline I think so what UNIX does
is it looks for all the space characters
in the sentence and that's what it uses
to figure out which word has to go in
which positional parameter so I have my
text editor here and I have saved this
file in the home folder it's called ifs
and has the extension SH and what I'm
going to do in the script file is I'm
going to first declare a variable and
then use set to set the positional
parameters with the words in the
variable and then I'm going to change
the value of ifs and show you guys how
the behavior of the set command is
modified right so let me first create a
variable I'll call it line and I'll give
it value shell scripting is fun and
remember since it's a string variable
I've put the sentence within double
quote
right on the next line I'm gonna use set
and as an argument to it I'm going to
pass the variable line but with the
dollar symbol right because we are
interested in setting the positional
parameters with the words that are
stored in the variable line and not with
just the word line on the next line I'm
going to use echo statement to echo out
the value of dollar one and well
actually since for positional parameters
must have been set with the sentence I'm
going to use for echo statements to echo
out the four words on different lines
right so dollar two and dollar three and
dollar four and let me save this file
bring up my terminal again I'll clear
the screen and when I execute the script
by typing in SH space ifs dot Sh which
is a name of a file and you see that on
four different lines you see the four
words in the sentence that's because
there is a space character between you
know the words in the sentence but if I
change the value of ifs by typing in ifs
is equal to colon right let me save this
file and let me clear the screen and
when I execute the script now you see
that the entire sentence shell scripting
is fun is being displayed on one line
and then you see three blank lines of
output and that's because UNIX started
looking for the colon character instead
of the space character this time in the
sentence and since it didn't find any
colon characters they thought that okay
maybe this entire thing has to go in
dollar one and dollar to dollar $3 for
didn't get any values right and that's
why you saw three blank lines and these
three echo statements are responsible
for them right so if I would replace the
space characters in the sentence with
the colon characters and you would see
that the original behavior of the set
command would be restored right and
that's not going to be difficult for me
to do and let me first clear the screen
and when I execute the script you see
that you know once again I see the four
words on four different lines
so understanding ifs is important
because not always you deal with the
text input that has a space character as
a delimiter for example in the previous
tutorial we talked about the password
file and I told you guys that in the
password file in each row you have seven
fields and all the fees are separated
from each other with the colon character
and not the space or tab right so you
know if you're dealing with a file such
as the password file or if you are
dealing with a file that's you know a
bit using a software like Excel where
you can have files in CSV format that is
comma separated value where you have the
comic actor is a delimiter you would
want to first change the value of ifs by
typing in ifs and then using the equal
to symbol and the value that you want
assigned a weight before actually using
the set command and setting your
positional parameter right so another
thing that you have to note is that
whenever you use ifs in your shell
scripts you have to type in the three
characters in uppercase you don't have
to type them in lowercase if you do that
let one work right so in the next
tutorial we're going to check out
something interesting again so stay
tuned and subscribe to my channel for
more updates I see you guys in the next
tutorial thank you so much for watching
this one