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By default, terminals run a program called a shell.
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The terminal is a text interface.
0:00
By default,
terminals run a program called a shell.
0:02
There are many different
shell programs available,
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most of them with names ending in SH,
like ZSH, KSH, and so on.
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Most operating systems today
run a shell called Bash, and
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that's what we're running here.
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All the different shells
work very similarly, so
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the things you'll learn in Bash will
be applicable in the other shells too.
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You can see a bunch of text here,
ending in a dollar sign.
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This is the shell prompt, the shell
is prompting you to type something.
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Most shell prompts end with a dollar sign,
like this.
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The blinking box following
the dollar sign is the cursor,
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it's the place the text
you type will appear.
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It mostly works like the cursors you've
seen in word processors and web forms, but
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with a few exceptions.
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You can type text with the letter
keys on your keyboard, and
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you can delete it with the backspace key.
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You can move back and
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forth within the text you've typed on this
line with the left and right arrow keys.
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But you can only type on this one line,
you can't move off of it.
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If you press the up and
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down arrow keys, it will instead cycle
through entries you've made previously.
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Here you can see it bringing
up commands I entered before.
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This is called command history, and we'll
talk about it more in an upcoming video.
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If I hit the Enter key without typing
anything, it won't really do anything,
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it'll just display another prompt.
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We can run commands at the prompt to
execute other programs inside the shell.
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The output of these commands
will be shown in the terminal.
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Because the shell offers you a single
line of text where you enter commands,
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this is often referred
to as the command line.
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Let's try running a program called ls,
which is used for listing files.
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I type ls and
press the Enter key to run the command.
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The program runs, and its output appears
on the terminal below the command line.
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The program prints out
the names of several files.
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Then the ls program finishes, and
we're returned to our shell prompt.
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The shell is ready for
us to type another command.
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Let's try running another program.
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This time we'll run the whoami command,
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which prints the name of
the current user account.
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It looks like we're logged in
as a user named treehouse.
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Once again, the program completes and
we're returned to the shell prompt.
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Now I'll run a program called cat,
which concatenates or
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joins the contents of files together.
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Normally, you'd provide the names of one
or more files you want cat to print out.
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But since I didn't provide any, the cat
program sits there waiting for input.
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I don't want to use this right now,
so I'm going to stop the cat program.
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To do this, I hold down the Ctrl key
on my keyboard and press the C key.
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This special key combination sends
a signal to the program telling it that I
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want to quit.
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Any time a terminal program
appears to be stuck or
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isn't doing what you want, you can
press Ctrl+C to send it this signal.
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Most of the time, the program will quit
and return you to the shell prompt, so
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you can run another command.
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By the way, you may be wondering
what's up with these crazy command
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names like ls and cat.
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When you're working in the terminal,
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there are certain commands
you'll be using a lot.
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You don't wanna have to type
the word list over and over, so
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the command name is abbreviated to ls.
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You don't wanna type
concatenated all the time, so
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the name is shortened to cat, and so on.
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The abbreviations take a little extra
time when you're learning the commands.
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But believe me, they'll save you
some typing in the long run.
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Let me run one more program, clear.
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The clear program clears output
from the terminal screen,
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moving the prompt up to the top.
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By default, Bash shell also
supports a keyboard shortcut that
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does the same thing,
just hold the Ctrl key and press L.
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You don't have to remember
this key combination,
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it's not as important as Ctrl+C.
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But if you see me clear
the screen during this course,
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you'll know I did it by pressing Ctrl+L.
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Before we move on, I should point out
a couple more aspects of the prompt.
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This prompt shows the name of
the current user, treehouse.
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Then it shows the directory or folder that
we're in, ~/workspace, or just workspace.
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I can change to a different directory, and
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the directory name will be updated
when the new prompt is shown.
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We'll talk more about directories
and the cd command later.
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As I mentioned before,
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the end of the prompt is usually marked
with a dollar sign for normal users.
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This could be changed, but
it's conventional to use a dollar sign.
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The prompt is customizable, so
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don't worry too much if the prompt
on your system shows different info.
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Now you know how to enter
commands in the shell.
4:42
Up next, we'll look at ways to change
the behavior of those commands.
4:44
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