Shell Scripting Tutorial-54: More on Metacharacters 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 54th tutorial
in the series of tutorials on UNIX shell
scripting in this tutorial we're going
to check out a few meta characters and
we are not going to make a new shell
script instead whatever we're going to
learn we're gonna learn through the
terminal so I'll bring up my terminal
and the first thing that we're going to
learn to do is to execute more than one
commands on one line what I mean by that
is if you type in a few commands let's
say LS and gal and echo with a message
within double quotes and press the Enter
key then you would see error messages
and that's because it's not allowed to
execute more than one commands on one
line in this way instead you would have
to use a metal character in between the
commands in order to instruct the shell
that you want these commands to be
executed in sequence right so I'll type
in LS and then I'll type in a semicolon
and then I'll type in Cal which is going
to be my second command I'll type in
another semicolon and then well let me
use banner to display a message instead
so I just display hello when I press the
Enter key now you see that I first get
the names of all the files and folders
in my home folder and that's because LS
was the first command in the list and
then Cal got executed that's why I see
my current month's calendar and then
banner got executed so I see the message
hello printed with the bound symbols so
that's what you have to do if you want
to execute more than one command
simultaneously if you were to do this in
a shell script then obviously it would
be easy because on line one you could
type in LS on line two you could type in
cat on line three you could type in echo
or banner or whatever and then execute
the shell script in the terminal and you
would just have to type in the name of
the shell script just once right so that
would have obviously been more
convenient but I wanted you guys to know
this semicolon meta character and its
significance that's why I discussed it
with you so the next thing that we're
going to learn to do is something that
you would normally achieve using the if
else construct initial script right so
in one of the tutorials in this course I
guess it was a one on draft I created a
text file in which I stored the innards
of the song money and it was called
taxin
skort file so let me just carry out the
contents of this 5tu on screen so that
we can be sure and there you go you see
the lyrics of the song and what I'm
going to do now is I'm going to use grep
to search for a pattern in this text
file and if that pattern is found I'm
going to redirect that pattern to
another text file and if that thing is
done successfully then I'm going to use
echo to display a message but you see
that if you would achieve this task in a
shell script then you would have to use
the if else construct but we're going to
learn to do this without using FS right
so I'll type in grep first and then I'll
make grep case-insensitive
by giving it the option - I and then
I'll type in the name of the pattern
that we wish to search for which is
going to be money and then the name of
the file in which we want the pattern to
be searched which is going to be text
underscore file and if statements are
found then we are going to redirect them
to another file called pattern and if
this entire thing is done then we are
going to use echo to display our message
right so the message that we're going to
display is the task was completed or
stopped in the end and when I press the
Enter key you see that echo got executed
and I get the message the task was
completed and if you would use cat to
see the contents of the file part then
you will see that it has six lines and
each of the six lines starts with the
word money so there were 52 lines in
total in the file txt underscore file
and are those lines there were six
statements and had the keyword money in
them and those six statements were first
redirected to the file pattern and since
the entire operation was performed
properly successfully the echo command
got executed and if you wanted to
execute the echo command irrespective of
the exit status of the command that you
have before the double ampersand
operator here then instead of the double
ampersand operator the operator that you
would have to use would be the double
pipe symbol right so this is the or
operator and what this does is it leads
to the execution of the second command
even if the first command fails to
execute successfully right so there you
go that's it for now I'll see you guys
in the neck
tutorial in which we discuss something
interesting again meanwhile thank you so
much for watching this video and please
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