Shell Scripting Tutorial-50: Fetch & Redirect Man Pages of commands using 'for loop' Video Lecture | Shell Scripting: Discovering to Automate Command-Line Tasks - Back-End Programming

hello guys my name is Wonder and welcome
to my channel this is the 50th tutorial
in the series of tutorials on UNIX shell
scripting in this video you will not
going to check out anything new or
specifically important I'm just going to
discuss an application of for loop which
I think you guys might find interesting
so I have my text editor here and I have
saved two files in my home folder the
one that I have opened up at the moment
is called command list and it's a text
file and the other one is a script file
and it's called help and has the
extension SH right so what we're going
to do in this tutorial is in the file
command list I'm going to type in a few
command names right and then in the
script file hepped or SH I'm going to
use for loop to I trade over the
commands that I will be diving in
command list and then I will be fetching
out the man pages of those commands one
by one and I will be sending those man
pages to another file which I'm going to
call help file right so firstly I'll
have to type in commands here and I'm
going to use cat and date and Cal and
touch these are probably the commands
that I use most often and in the file
health or SH I'll type in the keyword
for on line one because we are going to
use for do two I trade over the commands
and then I'll type in my control
variable which I'm going to call CMD
right and then I'll type in another
keyword in which is part of the for
syntax and then I have to inform for the
commands over which I wanted to I trade
and this I'm going to do by typing in
cat space command list and I'll put this
entire thing with in reverse codes and
the reason why I'm doing this is because
we are interested in the commands that
are there in the file command list and
since command list is a text file we are
using the cat command to tell us the
entries or the words that are there in
the file command list and once those
commands are made available 2 4 4 will I
trade over them one by one and the
control variable CMD will hold cat in
the first iteration and then date in the
second iteration Cal in the third
and touching the for titration so since
there are four commands that are going
to be for for loop iterations and let me
save this file first all right
and on the next line in my script file
I'm going to type in the keyword do to
get inside the for block and then since
I want to get the man pages of the
commands I'm going to type in man space
dollar CMD and what this will do is
since CMD is going to hold the commands
one by one so in the first iteration man
CMD will get the man page of cat in the
second iteration man CMD will get the
man page update and so on and so forth
there are going to be four iterations
and since I want to send this output to
another file I'm going to use the double
redirection operator and I'm going to
type in the name of the file which I'm
going to call help file right and I've
used the double redirection operator
here because I want the output to be
appended right so in the first iteration
cats main page is going to be sent to
have file and in the second iteration
the second command that we have the
command list file is dead
so dates man page will be appended to
the man page of character that is there
in the help file we don't want it to
replace the already existing test but we
want it to append the text to what's
already there in the hair file right so
I hope you get this and in case you have
any confusion check out my tutorial on
cat command and it's pretty early in
this course it has to be before the 15
tutorials so you guys can check that out
right and on the last line or sorry in
on the fourth line I'm going to type in
the last keyword which is done and with
this my job's over so now what I can do
is I can bring up my terminal and I'll
execute the script file by typing in SH
face help dot Sh
when I press the Enter key well it took
a second for the shell to do all that
work but my dog prompt has been returned
to me now and now what I can do is I can
open the file help file and see what I
have and I'm not going to do that in the
terminal instead I'm gonna use my text
editor and there you go in this file
help file it's obviously a text file you
see that you first have the man
page of cat and then from 77th line
onwards you have the man page of date
and then what dates man page is pretty
long because you get a lot of options
that you can use with it and then from
line 254 onwards you have the man page
of Cal and then lastly from line 347
onwards you have the man page of touch
so there you go all that work was done
by shell in just a few seconds and it's
pretty amazing how quickly things work
and you know this wasn't really a very
important tutorial and you guys could
have probably skipped it but you know I
just thought that it might be you know a
little bit of fun for you guys to do
something of this sort so thank you so
much for watching this tutorial in the
next tutorial we're going to discuss
nested loops which are obviously
important and we might be using them a
lot in this course and even otherwise
you know if you decide to become shell
programmers in future then nested loops
are something that you must know and
something that you must be able to use
as and when the need arises so thank you
so much for watching this one I see you
guys in the next tutorial please
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