Shell Scripting Tutorial-8: File Permissions 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 eighth
tutorial in the series of tutorials on
shell programming now in the last
tutorial I said that in this tutorial
we'll be checking out LS and I also told
you that it is a very important command
now before we check out LS I would like
to talk about file permissions because
you know I mean it's better to know
about files and permissions before we
learn LS so what I'm going to do now is
I'm going to create a file using the
terminal and the touch command and I'll
call this file anything I'll just call
it sample and in the home folder when I
right-click on the file that I've just
created and check out its properties I
can see in the permissions tab three
categories of users the first is the
owner and it has access read and write
to the file sample the next category is
the group to which the owner belongs and
the third category is for other users
people other users on the operating
system who are not in the same group as
the owner which in this case is me now
you would also see that at the end you
have a checkbox and a column execute and
this checkbox is unchecked which means
that none of these guys has permissions
to execute this file as a program and
these are default settings no matter
where you create your file in the file
system and no matter what name you give
it if you do not specifically mention
permissions of your own choice at the
time of creating your file your file
will have the same set of permissions as
you are seeing here now what do we mean
by read and write permissions for a file
but read permission we mean that we can
just open the file and we can just view
the contents of the file and we cannot
make any modifications to it and by
write permission we mean that we can
open the file in a text editor and we
can change the contents of ed we can
delete things we can add things and we
can save the new settings
with execute permission obviously we
mean that we can execute the file as a
program if it's a binary file or you
know if it's a shell script then we can
execute it in the terminal and we can do
those kind of things
now what else should I talk about yeah
the file permissions are read write and
execute all have certain numeric values
or indices associated to them read has a
numeric value for write has a numeric
value to and execute has a numeric value
one which means that a file at best
can have a total numeric value of 7
which is 4 plus 2 plus 1 and sorry and
as I said that when a file is created
neither the owner nor the group of the
owner and also the other people on the
operating system none of these guys has
permissions to execute so a file with
the default settings can have a best
value of 6 which is just read and write
right now at this point of time I would
like to talk about a variable you mask
now you mask is a system variable and
let me clear the terminal first and if I
just type in you mask in the terminal
and press Enter I see a number on my
screen and this number is a four-digit
number and the first digit tells me that
this is an octal number so just ignore
it and concentrate on the last three
digits the last 3 digits are 0 to 2 now
when a file is created what unique stars
is it subtracts this value of you mask
from the value 6 success for a file and
777 for a dietary so when you subtract 0
to 2 from 666 you get 6 for 4 and that
gives rise to the default settings for a
file which means that the owner of the
file can read and write that's 4 plus 2
6 and the group of the owner and other
people can just read the file and that's
given by 6 minus 2 4 and 6 minus 2 4
here so that is it I just wanted to give
you guys a little insight on file from
and this is actually pretty important
when we learn to use the chmod command
to change file permissions I'm going to
elaborate further on the concept of
umask and also on the concept of read
write and execute permissions for
directories but for the time being
that's that's all I wanted you guys know
so see you guys in the next tutorial
thank you so much for watching this one
and please subscribe to my channel