- All right, as I told you,
Linux is all about using commands.
So before we are starting to learn how to work
with many, many commands that are available on Linux,
first a few generic words.
The first thing to realize is that Linux is case sensitive.
That means that really it makes sense
if you use upper or lowercase,
and I can tell you all commands
that you are going to work with are lowercase.
So make sure that you are typing lowercase
because otherwise you will get an error message.
Also in Linux commands, go together with options.
An option is something that you put behind the name
of the command to change the behavior of the command.
And options exist as long options or as short options.
Long options will always start
with dash dash and short options normally start
with a single dash.
If you use, for instance, uname--help
then --help is the long option.
And if you use ls -lrt,
the -lrt is referring to three short options;
the L, the R, and the T.
And if you wanna know which options are available
you can use --help
on any command to learn how to use it.
Let's do a quick demo before we are moving over
to the next video.
All right, let me demonstrate the use of these options.
So ls --help.
I really like the --help
because that's printing the options that are available
and oh boy, that's a lot.
We will take care of that for later.
But what I want to show you is
that ls -- help is showing help.
You know what, let's do that on mkdir,
mkdir is for make directory.
At least it fits on one screen.
I'll tell you about the help text later.
What I want you to realize right now is
if we are using mkdir-help with a single minus instead
of a double minus, then I'm getting invalid option H.
So the single minus is interpreting H and E and L and P
and that is invalid.
So we need a double minus.
Let me also show you the uppercase thing.
If I would type LS in uppercase, then what do we get?
We get LS command not found.
In some cases your distribution
will tell you, "a LS command not found.
"Did you want to run LS in all lowercase?"
In this case, you can see that is not happening.
So the message here is in Linux,
mind the use of uppercase and lowercase.