REMI : In this video, we are going to see some commands,
that, when they are executed, don't go back to the prompt immediately.
Remember that the prompt is what is prompting for a command.
Here it's a tilde, a space, a dollar, a space, and a blinking cursor,
waiting for a command to be written and to enter  press
key so that we execute the command.
So when we execute some of the commands, they launch a program.
And this program will be interacting with the user-- with you--
until you quit this program and go back to the prompt.
So I'm going to show you some of these commands of these programs
that don't go back directly to the command prompt.
And we will have to find a way to quit--
to exit these programs--
to go back to the command line prompt.
So the first command will be top.
Let's first try to see the help and see what this command is doing.
So --help
and it provides a view of process activity in real time.
It displays a screen full of them.
And here you can see some keys.
And here, the most important one would be Q
that is exit , and also something here,
carrot C or the circumflex accent with a C.
It means that you have to press the Control key.
So the carrot is control key,
and at the same time, the C key.
So Control-C means that if you push these two buttons,
these two keys, then you will go back to the command prompt
and it will exit the command.
Let's try to do that.
Let's try to execute top.
And as you can see, the program is running.
And at the bottom left, you have this blinking cursor.
But you don't have the command prompt.
If I type something here, it doesn't do anything.
I just type S and it did something with the program anyway.
So let's try to type the Q key.
All right.
And now I have the command line prompt back again.
Let's try to go back to the top program.
And let's try to type Control C. Yeah, it works.
So both ways to exit the program and then go back to the command prompt.
Anyway, let's go back to top and see what's happening here.
We have some memory usage here, CPU usage, 0%
and the load average.
We'll see that later.
And we have a lot of programs running here,
a list of the programs.
And you will see here that the program top is running, with a PID at 56, 49 00:03:08,050 --> 00:03:10,410 a process identifier.
We'll see that later.
So anyway, it's a simple program to see what's happening in the system,
and to see for each program how much CPU it is using.
The percentage of the CPU used by top is 0.4%.
And so anyway, I wanted to show you how to get out of this application.
So type the Q or Control-C
Let's try another program--
htop.
Usually, it's not installed and you have to install it on a real Linux system.
So it's a top, but with a little bit more
designed interface even if it is textual, because you can see here
the CPU consumption in a more graphical way, and also the memory consumption.
Here, it's the memory that is used, and here, the memory that is free.
So we will use 2 megabytes out of 25 megabytes total.
The swap memory-- we won't use that.
And here, you see the command htop that is running with a process
identifier 57 and a CPU percentage. Oh, a little bit higher than top.
It's 3.9%.
And also the memory percentage,
3.7%,  and the time, how much CPU time it is using.
All right.
How do I quit this program?
Oh, you can see at the very bottom, that you have F1 and F2, et cetera,
up until F10 to quit.
So here, it's pretty obvious that we have
that we have to push the F10 key to get out of the program.
On some of the keyboards, you will have to find the F10 key,
and sometimes you have to press a special key to activate the function
keys, like F10.
So on my computer, I have to push a button that is called function-- fn--
and at the same time push the F10 key.
Is it working if I do that?
Yeah.
I just went back to the prompt as you can see.
So F10 worked.
Let's try to run again htop.
And let's try the Control C keys.
And it works indeed.
If I press the Enter key again, yeah, you
can see that I have the command line prompt again.
And let's try again htop and let's try this time the Q key.
And indeed it works also.
So this command htop you can get out, you
can exit the program with Q, Control C and the F10 keys.
Let's try another one :
nano.
nano is a file editor, a very basic one.
If I enter this program, you will see a kind of text editor.
And at the very bottom, you have a kind of menu.
It's a key menu.
And you can see here, we have always a carrot or the circumflex accent with G
to get help or carrot X to exit, or carrot O to write out
or to read a file, et cetera.
So here, I imagine that carrot X means that you
have to push the Control and the X keys to exit the program.
So let's try Control X, and indeed, we just exited nano.
Let's go back to nano, and let's try Control C, if it works.
Oh, it did something because you have something that is written here,
but he didn't exit the program.
So Control C is doing something, and indeed here,
you can see in the menu that Control-C and those,
I don't know, it's written curve pose, but I don't know what it means.
Maybe if I can get help.
So let's right Control J--
Control G, sorry.
Oh main nano help text, nice.
So here, you have a lot of explanation here.
If I use the arrows keys, I can scroll through all the help.
So anyway, let's try to exit again this program:
Control X and Control X. All right, and I went back to the command prompt.
Let's try to see another text editor that is very famous.
It's called vim,
v-i-m. This one is sometimes quite difficult to get out of.
Here, the first page explains how to exit the program.
Look here-- type-- colon Q and then Enter to exit.
Let's try that :Q Enter.
all right.
And I went back to the command prompt.
But vim is quite,
indeed sometimes, quite tricky to get out.
Let's try again.
If I type the i key, it goes to insert mode.
So I can type some text.
So first, I typed the i key.
It goes to insert mode and now I don't have the menu anymore,
and I'm kind of lost in the program.
The program is still running.
And if I try Q, well, anyway,  it doesn't work.
If I try Control C, it doesn't do anything.
And I cannot type any more.
Oh, I just typed some random key and I don't know what's happening.
So sometimes it's quite tricky to get out of vim.
Let's try :q Enter.
No write since last change,
add exclamation mark to override.
OK.
:q! mark
and I went back to the command prompt.
Let's try again.
vim,  let's try to type
i and then some text, and then...
ha, I'm quite blocked here, because if I type :q and Enter,
well it just enters the text.
So I have to go back to this kind of vim menu,
and to do that I have to push the Escape key.
Let's try it.
All right.
And then let's try again :q. All right,  the same message here,
so :q!  and indeed I went back to the command
prompt.
So vim is a quite difficult program to get out sometimes.
So anyway, in a vast majority of the cases,
you can use the Control and C keys.
So sometimes it's written carrot or the circumflex accent.
And it means control.
So Control-c is a good way to get out of a program,
but sometimes it doesn't work and you have to find another way.
You have to look through the help of the program
or get smart to get out and have the command prompt again.