0:00:00.650,0:00:07.799
all right everyone thanks for coming in.

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This is the missing semester of your CS Education;

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at least that's what we chose to call

0:00:09.960,0:00:13.679
the class. if you're not here for this

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class then you're in the wrong room. We

0:00:13.679,0:00:19.590
will be here for about an hour just to

0:00:15.900,0:00:21.180
set your expectations and I want to talk

0:00:19.590,0:00:23.789
to you a little bit first about why

0:00:21.180,0:00:25.980
we're doing this class. So this class

0:00:23.789,0:00:29.670
stems out of an observation that Anish

0:00:25.980,0:00:33.030
and Jose and I have made while TA-ing various

0:00:29.670,0:00:34.710
classes at MIT which is that basically

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all of us computer scientists, we know

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that computers are great at doing these

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repetitive tasks and automating things

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but we often fail to realize that there

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are lots of tools that can make our own

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development processes better. We can be a

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lot more efficient about how we use our

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computers because we can use the

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computer as a tool for ourselves not

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just for building websites or software

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those sorts of things and this class is

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an attempt to address - this is an attempt

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to show you some of the tools that you

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can use to great effect in your day to

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day in your research and in your studies

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and it's going to be a class where we

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want you to teach you both how to make

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the most of the tools that you already

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know but also hopefully teach you about

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some tools so you don't know from before

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and how to combine those tools to

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produce more powerful things than you

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think you might be able to do with what

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you know today the class is going to be

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structured as a series of 11 one-hour

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lectures and each one is going to cover

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a particular topic you can see the

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website which is also listed there for

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the list of lecture topics and what date

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will do each one they will mostly be

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independent and so you can sort of show

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up for the ones that you're interested

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in but we will sort of assume that

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you've been following along so that as

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we get to later lectures I'm not going

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to be teaching you bash all over again

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for example we we are also going to post

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both the lecture notes and recordings of

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the lectures online exactly when we do

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that we haven't established yet but it

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will be after the lectures obviously the

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videos have to be posted after

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the class is gonna be run by me John and

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Anne each sitting over there and Jose

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who is not currently here but we'll be

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holding tomorrow's lecture and keep in

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mind that we're trying to cover a lot of

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ground over the course of just 11

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one-hour lectures and so we will be

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moving relatively rapidly but please do

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stop us if there's anything where you

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feel like you're not following along if

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you feel like there's something you wish

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we would spend more time on just let us

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know please interrupt us with questions

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and also after each lecture we're going

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to hold office hours on the ninth floor

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of building 30 to the Stata Center of

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the computer science building as if you

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show up up in the ninth floor lounge

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there and the gates tower then you can

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come and try some of the exercises that

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we give for each lecture or just ask us

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other questions about things we've

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talked about in lecturer or other things

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about using your computer efficiently

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due to the limited time that we have

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available we're not going to be able to

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cover all tools and full detail and so

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we'll try to do is highlight interesting

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tools and interesting ways to use them

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we won't necessarily dig into the deep

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details about how all of it works or

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more elaborate use cases but if you have

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questions about them please come ask us

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about that too many of these tools are

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tools that we have used for years and we

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might be able to point you to additional

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interesting things you can do with them

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sort of like take advantage of the fact

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that we're here this class is going to I

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don't wanna say ramped up quickly but

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what's going to happen over the course

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of this particular lecture is that we'll

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cover many of the basics that we assume

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that you will know for the rest of the

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semester things like how to use your

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shell and your terminal and I'll explain

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what those are - those who you're not

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familiar with them and then will pretty

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quickly ramp up into more advanced tools

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and how to use them you can already see

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from the lecture notes the kind of

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topics that we're going to be covering

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and so that brings us to today's lecture

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in which we are going to cover the shell

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and the shell is going to be one of the

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primary ways that you interact with your

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computer once you want to do more things

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than what the sort of visual interfaces

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you might be used to allow you to do the

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visual interfaces are sort of limited in

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what

0:04:26.550,0:04:29.669
they allow you to do because you can

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only do the things that there are

0:04:29.669,0:04:34.919
buttons for sliders for input fields for

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often these textual tools are built to

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be both composable with one another but

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also to have tons of different ways to

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combine them or ways to program and

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automate them and that is why in this

0:04:42.960,0:04:48.060
class we will be focusing on these

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command line or text-based tools and the

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shell is the place that you would do

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most of this work so for those of you

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are not familiar with the shell most

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platform provides some kind of shell on

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Windows this is often PowerShell but

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there are also other shells available on

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Windows on Linux you will find tons of

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terminals these are windows that allow

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you to display shells and you'll also

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find many different types of shells the

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most common of which is bash or the born

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again shell because it's such a common

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shell it is the one we're primarily

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going to be covering in these lectures

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if you're on Mac OS you will probably

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also have bash maybe an older version of

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it if you open the terminal app and so

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if you want to follow along on any of

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these platforms feel free but keep in

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mind that most of this is going to be

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sort of Linux centric in terms of how we

0:05:32.520,0:05:39.000
teach it even though most of these tools

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work on all the platforms if you want to

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install a terminal and a shell and you

0:05:40.409,0:05:45.330
don't know how to do it well we're happy

0:05:42.539,0:05:47.400
to show you at office hours or it's

0:05:45.330,0:05:51.599
usually very easy to just Google like

0:05:47.400,0:05:57.060
your platform plus like terminal and you

0:05:51.599,0:05:59.039
will get one now when you open a

0:05:57.060,0:06:01.169
terminal you get something that looks a

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little bit like this so it will usually

0:06:01.169,0:06:06.000
have just a single line at the top and

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this is what's known as the shell prompt

0:06:06.000,0:06:10.020
you can see that my shell prompt looks

0:06:07.710,0:06:12.090
like this it has my user name the name

0:06:10.020,0:06:14.219
of the machine that I'm on the current

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path I'm on and we will talk about paths

0:06:14.219,0:06:18.719
a little bit later and then it's really

0:06:16.770,0:06:20.969
just sort of blinking they're asking me

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for input and this is the shell prompt

0:06:20.969,0:06:25.860
where you tell the shell what you want

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it to do and you can customize this

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prompt a lot and when you open it on

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your machine it might not look exactly

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like this it might look something like

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this if you've configured it a little or

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it might look all sorts of different

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ways we won't go too much into

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customizing your shell in this

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particularly

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we'll do that later here we're just

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going to talk about how do you use this

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shell to do useful things and this is

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our the main textual interface you have

0:06:49.860,0:06:53.430
to your computer's through this shell on

0:06:51.750,0:06:55.950
the shell prompt you get to write

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commands and commands can be relatively

0:06:55.950,0:07:00.570
straightforward things usually it'll be

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something like executing programs with

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arguments what does that look like well

0:07:02.550,0:07:06.210
one program we can execute is the date

0:07:04.470,0:07:07.380
program we just type date and press

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enter and then it will show you

0:07:07.380,0:07:12.330
unsurprisingly the date and time you can

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also execute a program with arguments

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this is one way to modify the behavior

0:07:14.850,0:07:20.760
of the program so for example there is a

0:07:17.790,0:07:22.410
program called echo and echo just prints

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out the arguments that you give it and

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arguments are just white space separated

0:07:25.050,0:07:29.820
things that follow the program name so

0:07:27.330,0:07:30.720
we can say hello and then it will print

0:07:29.820,0:07:32.940
hello back

0:07:30.720,0:07:35.610
perhaps not terribly surprising but this

0:07:32.940,0:07:37.050
is the very basics of arguments one

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thing that you'll notice is that I said

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that arguments are separated by

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whitespace and you might wonder well

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what if I want an argument as multiple

0:07:42.060,0:07:47.220
words you can also quote things so you

0:07:44.310,0:07:50.310
can do things like echo hello space

0:07:47.220,0:07:52.710
world and now the echo program receives

0:07:50.310,0:07:55.380
one argument that contains the string

0:07:52.710,0:07:57.540
hello world with a space well you can

0:07:55.380,0:07:58.770
also use single quotes for this and the

0:07:57.540,0:08:00.480
difference between single quotes and

0:07:58.770,0:08:03.420
double quotes will get back to and when

0:08:00.480,0:08:06.120
we talk about bash scripting you can

0:08:03.420,0:08:09.000
also just escape single characters so

0:08:06.120,0:08:12.150
for example hello world this will also

0:08:09.000,0:08:15.720
work just fine all of these rules about

0:08:12.150,0:08:17.340
how you escape and how you parse and

0:08:15.720,0:08:19.590
quote various arguments and variables

0:08:17.340,0:08:21.330
we'll cover a little bit later hopefully

0:08:19.590,0:08:23.520
you won't run into too many we oughta

0:08:21.330,0:08:26.070
tease about this just keep in mind at

0:08:23.520,0:08:27.930
least that spaces separate arguments so

0:08:26.070,0:08:29.610
if you want to do something like make a

0:08:27.930,0:08:31.920
directory called my photos

0:08:29.610,0:08:33.780
you can't just type like make directory

0:08:31.920,0:08:35.880
my photos it will create two directories

0:08:33.780,0:08:40.010
one called my and one called photos and

0:08:35.880,0:08:43.229
that is probably not what you want now

0:08:40.010,0:08:45.600
one thing you might ask is how does the

0:08:43.229,0:08:48.839
shell know what these programs are when

0:08:45.600,0:08:50.700
I type date or when I type echo how does

0:08:48.839,0:08:53.190
it know what these programs are supposed

0:08:50.700,0:08:54.000
to do and the answer to this is your

0:08:53.190,0:08:55.439
program your

0:08:54.000,0:08:57.000
computer has a bunch of built-in

0:08:55.439,0:08:59.759
programs that comes with the machine

0:08:57.000,0:09:02.579
just like you your machine my chip with

0:08:59.759,0:09:05.339
like the terminal app or it might chip

0:09:02.579,0:09:07.800
with like Windows Explorer or at my chip

0:09:05.339,0:09:09.569
with some kind of browser it also ships

0:09:07.800,0:09:11.639
with a bunch of terminal centric

0:09:09.569,0:09:14.819
applications and these are stored on

0:09:11.639,0:09:18.209
your file system and your shell has a

0:09:14.819,0:09:19.949
way to determine where a program is

0:09:18.209,0:09:22.459
located basically has a way to search

0:09:19.949,0:09:24.620
for programs it does this through

0:09:22.459,0:09:27.389
something called an invariant

0:09:24.620,0:09:29.970
environment variable an environment

0:09:27.389,0:09:31.560
variable is a variable like you might be

0:09:29.970,0:09:33.899
used to for programming languages it

0:09:31.560,0:09:35.160
turns out that the shell and the

0:09:33.899,0:09:37.350
bourne-again shell in particular is

0:09:35.160,0:09:39.420
really a programming language this

0:09:37.350,0:09:41.550
prompt that you're given here is not

0:09:39.420,0:09:43.470
just able to run a program with

0:09:41.550,0:09:46.470
arguments. You can also do things like

0:09:43.470,0:09:47.910
while loops, for loops, conditionals...

0:09:46.470,0:09:49.860
All of these - you can define

0:09:47.910,0:09:51.000
functions, you can have variables, and all

0:09:49.860,0:09:52.860
of these things you can do in the shell.

0:09:51.000,0:09:56.399
We'll cover a lot of that in the next

0:09:52.860,0:09:57.990
lecture, on shell scripting. For now,

0:09:56.399,0:09:59.790
though, let's just look at this

0:09:57.990,0:10:01.199
particular environment variable.

0:09:59.790,0:10:02.699
Environment variables are things that

0:10:01.199,0:10:04.829
are set whenever you start your shell

0:10:02.699,0:10:06.600
they're not things you have to set every

0:10:04.829,0:10:08.160
time you run your shell there are a

0:10:06.600,0:10:09.750
bunch of these that are set things like

0:10:08.160,0:10:11.850
where is your home directory what is

0:10:09.750,0:10:13.079
your username and there's also one

0:10:11.850,0:10:16.170
that's critical for this particular

0:10:13.079,0:10:18.930
purpose which is the path variable so if

0:10:16.170,0:10:22.589
I echo out dollar path this is going to

0:10:18.930,0:10:25.100
show me all of the paths on my machine

0:10:22.589,0:10:27.930
that the shell will search for programs

0:10:25.100,0:10:30.870
you'll notice that this is a list that

0:10:27.930,0:10:33.000
is colon separated it might be kind of

0:10:30.870,0:10:36.000
long and hard to read but the essentials

0:10:33.000,0:10:38.279
is that - whenever you type the name of

0:10:36.000,0:10:41.610
a program is gonna search through this

0:10:38.279,0:10:43.769
list of paths on your machine and it's

0:10:41.610,0:10:46.920
gonna look in each directory for a

0:10:43.769,0:10:49.110
program or a file whose name matches the

0:10:46.920,0:10:51.029
command you try to run so in my case

0:10:49.110,0:10:52.800
when I try to run date or echo it's

0:10:51.029,0:10:54.509
gonna walk through these one at a time

0:10:52.800,0:10:56.370
until it finds one that contains the

0:10:54.509,0:10:58.410
program called date or echo and then

0:10:56.370,0:11:00.000
it's gonna run it if we want to know

0:10:58.410,0:11:01.649
which one it actually runs there's a

0:11:00.000,0:11:04.620
command called which which lets us do

0:11:01.649,0:11:07.500
that so I can type which echo and will

0:11:04.620,0:11:10.830
tell me that if I were to run a program

0:11:07.500,0:11:12.720
called echo I would run this one it's

0:11:10.830,0:11:16.350
worth pausing here to talk about what

0:11:12.720,0:11:18.620
paths are so paths are a way to name the

0:11:16.350,0:11:21.630
location of a file on your computer on

0:11:18.620,0:11:24.780
Linux and Oh Mac OS these paths are

0:11:21.630,0:11:28.170
separated by slashes forward slashes so

0:11:24.780,0:11:30.930
you'll see here that this is in the in

0:11:28.170,0:11:32.760
the root directory so the slash at the

0:11:30.930,0:11:34.850
very beginning indicates that this is

0:11:32.760,0:11:37.710
starting from the top of the file system

0:11:34.850,0:11:40.980
then look inside the directory called

0:11:37.710,0:11:43.580
USR then look inside the directory bin

0:11:40.980,0:11:46.440
and then look for the file called echo

0:11:43.580,0:11:48.620
on windows paths like this are usually

0:11:46.440,0:11:51.900
separated by back slashes instead and

0:11:48.620,0:11:53.640
we're on Linux and Mac OS everything

0:11:51.900,0:11:56.370
lives under the root name space so all

0:11:53.640,0:12:00.270
paths start with a slash or all absolute

0:11:56.370,0:12:02.070
paths on Windows there is one root for

0:12:00.270,0:12:05.130
every partition so you might have seen

0:12:02.070,0:12:08.220
things like C colon backslash or D colon

0:12:05.130,0:12:11.340
backslash so Windows has separate sort

0:12:08.220,0:12:13.050
of file system path hierarchies for each

0:12:11.340,0:12:14.850
each Drive that you have

0:12:13.050,0:12:18.540
whereas on Linux and Mac OS these are

0:12:14.850,0:12:20.010
all mounted under one namespace you'll

0:12:18.540,0:12:21.690
notice that I said the word absolute

0:12:20.010,0:12:27.360
path and you might not know what that

0:12:21.690,0:12:29.460
means so absolute paths are paths that

0:12:27.360,0:12:31.890
fully determine the location of a file

0:12:29.460,0:12:33.720
so in this case this is saying this is

0:12:31.890,0:12:36.540
talking only about a specific echo file

0:12:33.720,0:12:39.030
and it's giving you the the full path to

0:12:36.540,0:12:42.839
that file but there are also things

0:12:39.030,0:12:45.240
known as relative paths so a relative

0:12:42.839,0:12:49.320
path is relative to where you currently

0:12:45.240,0:12:52.490
are and so the way we find out where we

0:12:49.320,0:12:56.190
currently are is you can type PWD for

0:12:52.490,0:13:00.060
present working directory present print

0:12:56.190,0:13:02.700
working directory so if I type PWD it

0:13:00.060,0:13:05.790
will print out the current path that I'm

0:13:02.700,0:13:08.220
in right so currently I'm in the home

0:13:05.790,0:13:11.030
directory under the root and then John

0:13:08.220,0:13:14.730
under that and then dev under that etc

0:13:11.030,0:13:16.770
from here I can then choose to change my

0:13:14.730,0:13:18.540
current working directory and all

0:13:16.770,0:13:20.190
relative paths are relative to the

0:13:18.540,0:13:21.329
current working directory which is

0:13:20.190,0:13:24.629
basically where you

0:13:21.329,0:13:28.709
they are in this case for example I can

0:13:24.629,0:13:30.449
do CD / home CDs change directory this

0:13:28.709,0:13:32.610
is the way that I change what my current

0:13:30.449,0:13:34.829
working directory is in this case I

0:13:32.610,0:13:37.889
change to home and I am now you'll see

0:13:34.829,0:13:40.619
my my shell prompt change to say that I

0:13:37.889,0:13:42.660
am now in home it just gives me the name

0:13:40.619,0:13:44.220
of the last segment of the path but you

0:13:42.660,0:13:45.509
can also configure your terminal to give

0:13:44.220,0:13:50.309
you the full path whenever you're

0:13:45.509,0:13:53.100
anywhere and now if I type PWD again it

0:13:50.309,0:13:54.869
will tell me I'm in slash home there are

0:13:53.100,0:13:59.100
also a couple of special directories

0:13:54.869,0:14:03.149
that exist there is dot and dot dot dot

0:13:59.100,0:14:05.129
means the current directory dot dot

0:14:03.149,0:14:06.749
means the parent directory so this is a

0:14:05.129,0:14:09.540
way that you can easily navigate around

0:14:06.749,0:14:13.079
the system for example here if I type CD

0:14:09.540,0:14:15.179
dot dot it will tell me that I am now in

0:14:13.079,0:14:17.639
slash so I'm now in the root of the file

0:14:15.179,0:14:22.139
system I was in slash home now I'm in

0:14:17.639,0:14:24.869
slash and indeed if I type PWD well it

0:14:22.139,0:14:26.790
will do that right thing and I can also

0:14:24.869,0:14:28.980
then use relative paths to go down into

0:14:26.790,0:14:31.769
the file system right so I can do CD dot

0:14:28.980,0:14:34.079
slash home and this is gonna CD into the

0:14:31.769,0:14:36.899
home directory under the current

0:14:34.079,0:14:39.839
directory right so this will bring me

0:14:36.899,0:14:42.119
back to slash home if I now tried CD dot

0:14:39.839,0:14:44.100
slash home again it will say there's no

0:14:42.119,0:14:45.569
such directory because there is no home

0:14:44.100,0:14:49.429
directory under the current directory

0:14:45.569,0:14:53.699
I'm on which I changed by doing CD right

0:14:49.429,0:14:57.509
and I can sort of see de all the way

0:14:53.699,0:15:01.110
back to the place that I was using

0:14:57.509,0:15:07.040
relative paths and I can also do things

0:15:01.110,0:15:09.059
like dot dot dot dot dot to get back to

0:15:07.040,0:15:10.649
somewhere deep in my file system this

0:15:09.059,0:15:13.019
happens to be all the way back to the

0:15:10.649,0:15:15.629
root so here there's a bin directory and

0:15:13.019,0:15:17.850
another bin there's an echo file and so

0:15:15.629,0:15:20.309
then I could do world and that runs the

0:15:17.850,0:15:22.079
echo program under bin alright so this

0:15:20.309,0:15:24.439
is a way that you can construct paths to

0:15:22.079,0:15:26.579
arbitrarily traverse your filesystem

0:15:24.439,0:15:28.379
sometimes you want to absolute paths and

0:15:26.579,0:15:29.789
sometimes you want relative ones usually

0:15:28.379,0:15:33.179
you want to use whichever one is shorter

0:15:29.789,0:15:34.390
but if you want to for example run a

0:15:30.629,0:15:34.390
program or write

0:15:34.390,0:15:38.980
a program that runs the program like

0:15:36.940,0:15:41.830
echo or date and you want it to be able

0:15:38.980,0:15:43.660
to run be run from anywhere you either

0:15:41.830,0:15:45.640
want to just give the name of the

0:15:43.660,0:15:47.770
program like date or echo and let the the

0:15:45.640,0:15:49.720
shell use the path to figure out where

0:15:47.770,0:15:51.670
it is or you want to give its absolute

0:15:49.720,0:15:53.500
path because if you gave a relative path

0:15:51.670,0:15:55.840
then if I ran it in my home directory

0:15:53.500,0:16:01.720
and you ran it in some other directory

0:15:55.840,0:16:04.600
it might work for me but not for you in

0:16:01.720,0:16:06.340
general when we run a program it is

0:16:04.600,0:16:08.320
going to be operating on the current

0:16:06.340,0:16:09.910
working directory at least by default

0:16:08.320,0:16:11.980
unless we give it any other arguments

0:16:09.910,0:16:13.750
and this is really handy because it

0:16:11.980,0:16:15.730
means that often we don't have to give

0:16:13.750,0:16:17.680
full paths for things we can just use

0:16:15.730,0:16:20.050
the name of files and in the directory

0:16:17.680,0:16:22.570
that we're currently in one thing that's

0:16:20.050,0:16:24.280
really useful is to figure out what is

0:16:22.570,0:16:26.410
in the current directory we're in so we

0:16:24.280,0:16:28.060
already saw PWD which prints where you

0:16:26.410,0:16:31.090
currently are there's a command called

0:16:28.060,0:16:33.310
LS which will show you it will list the

0:16:31.090,0:16:35.980
files in the current directory so if i

0:16:33.310,0:16:38.050
type LS here this is all the files in

0:16:35.980,0:16:39.850
the current directory right and this is

0:16:38.050,0:16:43.420
a handy way to just quickly navigate

0:16:39.850,0:16:46.930
through the filesystem you'll see that

0:16:43.420,0:16:48.490
if I sort of CD dot and then do LS it'll

0:16:46.930,0:16:53.370
show me the files in that directory

0:16:48.490,0:16:56.260
instead but with LS I can also give it

0:16:53.370,0:16:58.360
LS dot dot like I can give it a path and

0:16:56.260,0:16:59.920
then will LS that file instead of the

0:16:58.360,0:17:04.270
one that I'm currently in or LS that

0:16:59.920,0:17:05.829
directory and you can see this if I go

0:17:04.270,0:17:09.220
all the way to the root as well right

0:17:05.829,0:17:11.560
root has different files one handy trick

0:17:09.220,0:17:13.570
you might not know about here is there

0:17:11.560,0:17:16.570
are two other special things you can do

0:17:13.570,0:17:18.339
one is the tilde character this

0:17:16.570,0:17:21.130
character brings you to your home

0:17:18.339,0:17:23.140
directory so tilde always expands to the

0:17:21.130,0:17:25.780
home directory and you can do relative

0:17:23.140,0:17:30.040
paths to it so I can do tilde slash dev

0:17:25.780,0:17:32.980
slash P DOS classes missing semester and

0:17:30.040,0:17:36.670
now I'm there because tilde expanded to

0:17:32.980,0:17:39.460
slash home slash John there is also for

0:17:36.670,0:17:42.250
CD in particular a really handy argument

0:17:39.460,0:17:44.530
you can give which is - if you do CD -

0:17:42.250,0:17:47.380
it will CD to the directory you were

0:17:44.530,0:17:48.180
previously in so if I do CD - I go back

0:17:47.380,0:17:52.230
to root

0:17:48.180,0:17:53.880
if I do CD - again I go back to missing

0:17:52.230,0:17:55.080
semester so this is a handy way if you

0:17:53.880,0:18:01.290
want to toggle between two different

0:17:55.080,0:18:03.570
directories in the case of LS or in the

0:18:01.290,0:18:06.180
case of CD there might be arguments do

0:18:03.570,0:18:07.560
you don't know about right currently we

0:18:06.180,0:18:09.510
haven't really been doing anything

0:18:07.560,0:18:11.520
except giving paths but how do you even

0:18:09.510,0:18:14.250
discover that you can give a path to LS

0:18:11.520,0:18:16.530
in the first place well most programs

0:18:14.250,0:18:18.840
take what are known as arguments like

0:18:16.530,0:18:21.570
flags and options these are things that

0:18:18.840,0:18:24.810
usually start with a - one of the Hemi

0:18:21.570,0:18:26.880
is one of these is - help most programs

0:18:24.810,0:18:30.000
implement this and if you run for

0:18:26.880,0:18:34.020
example LS - help it all helpfully print

0:18:30.000,0:18:36.000
out a bunch of information about that

0:18:34.020,0:18:38.400
command and you'll see here that it says

0:18:36.000,0:18:40.260
the usage is LS and you can give some

0:18:38.400,0:18:42.030
number of options and you can give some

0:18:40.260,0:18:46.350
number of files the way to read that

0:18:42.030,0:18:48.600
usage line is triple dot means one like

0:18:46.350,0:18:50.850
zero or one or more and the square

0:18:48.600,0:18:52.890
bracket means optional so in this case

0:18:50.850,0:18:54.300
there's an optional number of options

0:18:52.890,0:18:56.790
and there's an optional number of files

0:18:54.300,0:18:58.740
and you'll see that it says what the

0:18:56.790,0:19:00.720
program does and also specifies a number

0:18:58.740,0:19:03.000
of different types of flags and options

0:19:00.720,0:19:04.950
you can give usually we call things that

0:19:03.000,0:19:07.830
are a single dash in a single letter a

0:19:04.950,0:19:09.900
flag and anything that or anything that

0:19:07.830,0:19:11.730
doesn't take a value a flag and anything

0:19:09.900,0:19:16.640
that does take a value an option so for

0:19:11.730,0:19:22.260
example - a and - all are both flags and

0:19:16.640,0:19:24.180
- C or - color R is an option one thing

0:19:22.260,0:19:30.330
you'll see under here if you scroll down

0:19:24.180,0:19:37.140
far enough is the - L flag and that's

0:19:30.330,0:19:39.480
unhelpful the - L flag the - L flag uses

0:19:37.140,0:19:40.860
a long listing format now that's

0:19:39.480,0:19:43.350
particularly helpful in and of itself

0:19:40.860,0:19:46.890
but let's see what it actually does so

0:19:43.350,0:19:48.450
if I do LS dash L it still prints the

0:19:46.890,0:19:49.890
files in the current directory but it

0:19:48.450,0:19:52.170
gives me a lot more information about

0:19:49.890,0:19:54.600
those files and this is something you'll

0:19:52.170,0:19:56.280
find yourself using quite a lot because

0:19:54.600,0:20:00.810
the additional information it gives you

0:19:56.280,0:20:02.010
is often quite handy let's look at what

0:20:00.810,0:20:09.030
some of that information

0:20:02.010,0:20:10.110
ah so first of all the D at the

0:20:09.030,0:20:11.760
beginning of some of these entries

0:20:10.110,0:20:14.820
indicate that something is a directory

0:20:11.760,0:20:16.020
so the underscore data entry here for

0:20:14.820,0:20:18.690
example is a directory

0:20:16.020,0:20:22.650
whereas for for hTML is not a directory

0:20:18.690,0:20:25.410
it's a file the following letters after

0:20:22.650,0:20:28.650
that indicate the permissions that are

0:20:25.410,0:20:30.810
set for that file so this like we saw

0:20:28.650,0:20:32.640
earlier I might not be able to open a

0:20:30.810,0:20:34.170
given file or I might not be able to CD

0:20:32.640,0:20:35.760
into a given directory and this is all

0:20:34.170,0:20:37.980
dictated by the permissions on that

0:20:35.760,0:20:41.430
particular file or directory the way to

0:20:37.980,0:20:43.500
read these is that the the first group

0:20:41.430,0:20:45.810
of three are the permissions are set for

0:20:43.500,0:20:49.560
the owner of the file all of these files

0:20:45.810,0:20:52.020
you'll see are owned by me the second

0:20:49.560,0:20:53.880
group of three characters is for the

0:20:52.020,0:20:56.100
permissions for the group that owns this

0:20:53.880,0:20:58.650
file in this case all of these files are

0:20:56.100,0:21:01.770
also known by the john group and a final

0:20:58.650,0:21:03.900
group of three is a list of the

0:21:01.770,0:21:06.290
permissions for everyone else so anyone

0:21:03.900,0:21:08.550
who's not a user owner or a group owner

0:21:06.290,0:21:10.980
this directory is perhaps kind of boring

0:21:08.550,0:21:14.190
because all of the things are owned by

0:21:10.980,0:21:17.490
me but if we do something like CD to

0:21:14.190,0:21:20.280
slash and do LS dash L you'll see that

0:21:17.490,0:21:22.800
here all of them are owned by root we'll

0:21:20.280,0:21:24.090
get back to what the root user is but

0:21:22.800,0:21:26.400
here you see some of the permissions are

0:21:24.090,0:21:31.410
a little bit more interesting the groups

0:21:26.400,0:21:34.290
of three are read write and execute what

0:21:31.410,0:21:36.450
these mean differs for files and for

0:21:34.290,0:21:37.980
directories for files it's pretty

0:21:36.450,0:21:40.170
straightforward if you have read

0:21:37.980,0:21:41.820
permissions on a file then you can read

0:21:40.170,0:21:43.950
its contents if you have write

0:21:41.820,0:21:46.200
permissions on a file then you can save

0:21:43.950,0:21:48.270
the file you can add more to it or you

0:21:46.200,0:21:50.670
can replace it entirely and if you have

0:21:48.270,0:21:52.620
execute to the X bit on a file then

0:21:50.670,0:21:57.390
you're allowed to execute that file so

0:21:52.620,0:22:00.030
if we do LS al in slash bin that's a

0:21:57.390,0:22:02.640
novel and user bin you'll see that all

0:22:00.030,0:22:04.590
of them have the execute bit set even

0:22:02.640,0:22:06.480
for people who are not the owner of the

0:22:04.590,0:22:08.280
file and this is because the echo

0:22:06.480,0:22:09.420
program for example we want everyone on

0:22:08.280,0:22:11.700
the computer to be able to execute

0:22:09.420,0:22:13.920
there's no reason to say only certain

0:22:11.700,0:22:15.570
users can run echo that doesn't really

0:22:13.920,0:22:18.420
make any make any sense

0:22:15.570,0:22:20.960
for directories though these permissions

0:22:18.420,0:22:23.550
are a little bit different so read

0:22:20.960,0:22:26.460
translates - are you allowed to see

0:22:23.550,0:22:28.770
which files are inside this directory so

0:22:26.460,0:22:30.530
think of read as lists for a directory

0:22:28.770,0:22:33.420
are you allowed to list its contents

0:22:30.530,0:22:36.210
write for a directory is whether you are

0:22:33.420,0:22:39.090
allowed to rename create or remove files

0:22:36.210,0:22:42.030
within that directory so it's still kind

0:22:39.090,0:22:45.240
of right but notice that this means that

0:22:42.030,0:22:47.580
if you have write permissions on a file

0:22:45.240,0:22:49.950
but you do not have write permissions on

0:22:47.580,0:22:52.080
its directory you cannot delete the file

0:22:49.950,0:22:54.420
you can empty it but you cannot delete

0:22:52.080,0:22:57.660
it because that would require writing to

0:22:54.420,0:22:59.130
the directory itself and finally execute

0:22:57.660,0:23:01.950
on directories is something that trips

0:22:59.130,0:23:04.650
people up a lot execute on a directory

0:23:01.950,0:23:07.230
is what's known as search and that's not

0:23:04.650,0:23:10.200
terribly helpful a name but what that

0:23:07.230,0:23:13.470
means is are you allowed to enter this

0:23:10.200,0:23:15.240
directory if you want to get to a file

0:23:13.470,0:23:16.670
if you want to open it or read it or

0:23:15.240,0:23:20.310
write it whatever you want to do

0:23:16.670,0:23:22.710
basically to CD into a directory you

0:23:20.310,0:23:25.050
must have the execute permission on all

0:23:22.710,0:23:28.170
parent directories of that directory and

0:23:25.050,0:23:30.480
the directory itself so for example for

0:23:28.170,0:23:34.080
me to access a file inside slash user

0:23:30.480,0:23:35.820
slash bin such as user bin echo I must

0:23:34.080,0:23:38.100
have executed on route I must have

0:23:35.820,0:23:40.380
execute on user and I must have execute

0:23:38.100,0:23:42.120
on bin if I do not have all those

0:23:40.380,0:23:44.790
execute bits I will not be allowed to

0:23:42.120,0:23:48.410
access that file because I won't be able

0:23:44.790,0:23:50.670
to enter the directories along the way

0:23:48.410,0:23:52.560
there are a number of other bits that

0:23:50.670,0:23:55.320
you might come across like you might see

0:23:52.560,0:23:58.020
esses or T's in these lists you might

0:23:55.320,0:23:58.950
see LS those we can talk about in office

0:23:58.020,0:24:01.260
hours if you're curious

0:23:58.950,0:24:04.260
they will mostly not matter for anything

0:24:01.260,0:24:05.670
you will do in this class but they are

0:24:04.260,0:24:08.100
handy to know about so if you're curious

0:24:05.670,0:24:11.340
about them look them up on your own or

0:24:08.100,0:24:13.080
come ask us in office hours there are

0:24:11.340,0:24:14.580
some other programs that are handy to

0:24:13.080,0:24:16.200
know about oh sorry there's one more

0:24:14.580,0:24:17.400
thing as I mentioned if you just have a

0:24:16.200,0:24:19.470
dash it means you do not have that

0:24:17.400,0:24:21.810
permission right so if it says for

0:24:19.470,0:24:23.190
example our dash X it means that you

0:24:21.810,0:24:27.390
have read and execute but you do not

0:24:23.190,0:24:29.240
have right there are some other handy

0:24:27.390,0:24:32.360
programs to know about at this point

0:24:29.240,0:24:35.450
one of them is move or the MV command so

0:24:32.360,0:24:39.350
if I CD back to missing semester here MV

0:24:35.450,0:24:42.950
lets me rename a file and rename here

0:24:39.350,0:24:45.320
takes two paths it takes the old path in

0:24:42.950,0:24:47.870
the new path this is means that move

0:24:45.320,0:24:49.970
lets you both rename a file like if you

0:24:47.870,0:24:52.130
change the name of the file but not the

0:24:49.970,0:24:54.290
directory or it lets you move a file to

0:24:52.130,0:24:56.360
a completely different directory it just

0:24:54.290,0:24:57.890
you give the path to the current file

0:24:56.360,0:24:59.720
and the path to where you want that file

0:24:57.890,0:25:02.720
to be and that can change its location

0:24:59.720,0:25:05.480
and its name so for example I can move

0:25:02.720,0:25:09.020
dot files dot MD to be food MD

0:25:05.480,0:25:16.280
unhelpfully right and similarly I can

0:25:09.020,0:25:19.370
move it back there's also the CP command

0:25:16.280,0:25:21.860
the CP or copy is very similar it lets

0:25:19.370,0:25:23.750
you copy a file CP also takes two

0:25:21.860,0:25:25.610
arguments it takes the path you want to

0:25:23.750,0:25:28.340
copy from and the path you want to copy

0:25:25.610,0:25:30.890
to and these are full paths so I could

0:25:28.340,0:25:32.960
use this for example to say I want to

0:25:30.890,0:25:37.550
copy dot files out MD - dot dot slash

0:25:32.960,0:25:39.710
food MD sure food MD and now if I do LS

0:25:37.550,0:25:42.800
dot you'll see that there's a food MD

0:25:39.710,0:25:44.600
file in that directory so CP as well

0:25:42.800,0:25:47.780
take two paths it does not have to be in

0:25:44.600,0:25:49.700
the same directory and similarly there's

0:25:47.780,0:25:52.070
the RM command which lets you remove a

0:25:49.700,0:25:54.050
file and there - you can give paths in

0:25:52.070,0:25:56.750
this case I'm removing dot dot slash

0:25:54.050,0:25:59.480
food you should be aware for removing

0:25:56.750,0:26:01.940
especially on Linux removal is by

0:25:59.480,0:26:05.000
default not recursive so you cannot

0:26:01.940,0:26:07.100
remove a directory using RM you can pass

0:26:05.000,0:26:09.320
the - our flag which lets you do a

0:26:07.100,0:26:10.550
recursive remove and then give a path

0:26:09.320,0:26:12.890
that you want to remove and it will

0:26:10.550,0:26:16.370
remove everything below it there is also

0:26:12.890,0:26:18.290
the RM dr dir command which lets you

0:26:16.370,0:26:21.230
remove a directory but it only lets you

0:26:18.290,0:26:22.970
remove that directory if it is empty so

0:26:21.230,0:26:23.960
the idea here is to sort of be a safety

0:26:22.970,0:26:25.429
mechanism for you so you don't

0:26:23.960,0:26:28.610
accidentally throw away a bunch of your

0:26:25.429,0:26:31.040
files and the final little command

0:26:28.610,0:26:32.540
that's handy to use is make there which

0:26:31.040,0:26:34.429
lets you create a new directory and as

0:26:32.540,0:26:36.110
we talked about before you don't want to

0:26:34.429,0:26:37.940
do something like this because it will

0:26:36.110,0:26:40.580
create two directories for you one

0:26:37.940,0:26:42.140
called my and one called photos if you

0:26:40.580,0:26:42.980
actually want to create a directory like

0:26:42.140,0:26:50.120
this you would either

0:26:42.980,0:26:52.519
escape the space or quote the string if

0:26:50.120,0:26:54.919
you ever want more information about how

0:26:52.519,0:26:57.049
any command to basically on these

0:26:54.919,0:26:58.220
platforms work there's a really handy

0:26:57.049,0:27:00.649
command for that as well

0:26:58.220,0:27:04.610
there is the program called man for

0:27:00.649,0:27:06.409
manual pages this program takes as an

0:27:04.610,0:27:09.080
argument the name of another program and

0:27:06.409,0:27:12.019
gives you its manual page so for example

0:27:09.080,0:27:14.990
we could do man LS and this shows us a

0:27:12.019,0:27:16.730
manual page for LS you'll notice that in

0:27:14.990,0:27:19.250
the case of LS it is fairly similar to

0:27:16.730,0:27:20.870
what we got with LS - help but it's a

0:27:19.250,0:27:23.570
little easier to navigate a little

0:27:20.870,0:27:26.269
easier to read usually towards the

0:27:23.570,0:27:28.639
bottom you will also get examples

0:27:26.269,0:27:29.899
information about who wrote it where you

0:27:28.639,0:27:32.389
can find more information and that sort

0:27:29.899,0:27:32.990
of stuff one thing that can be confusing

0:27:32.389,0:27:35.330
sometimes

0:27:32.990,0:27:36.289
at least until a recent version where

0:27:35.330,0:27:38.779
they added this three at the bottom

0:27:36.289,0:27:41.389
which says Q to quit they do not use to

0:27:38.779,0:27:43.279
say this you press Q to quit this

0:27:41.389,0:27:48.169
program it can be really hard to quit it

0:27:43.279,0:27:50.750
if you do not know that a handy keyboard

0:27:48.169,0:27:52.970
shortcut here by the way is ctrl L which

0:27:50.750,0:27:56.990
lets you clear your terminal and go back

0:27:52.970,0:27:59.330
to the top so so far we've only talked

0:27:56.990,0:28:01.370
about programs in isolation but where

0:27:59.330,0:28:03.019
much of the power of the shell really

0:28:01.370,0:28:06.380
comes through is once you start

0:28:03.019,0:28:08.419
combining different programs right so

0:28:06.380,0:28:10.789
rather than just like running CDE

0:28:08.419,0:28:12.500
running LS and etc you might want to

0:28:10.789,0:28:13.940
chain multiple programs together you

0:28:12.500,0:28:15.980
might want to interact with files and

0:28:13.940,0:28:19.309
have files operate in between programs

0:28:15.980,0:28:21.200
and the way we can do this is using this

0:28:19.309,0:28:24.620
notion of streams that the shell gives

0:28:21.200,0:28:25.940
us every program by default has I'm

0:28:24.620,0:28:28.610
gonna simplify a little and say two

0:28:25.940,0:28:31.820
primary streams it has an input stream

0:28:28.610,0:28:33.950
and an output stream by default the

0:28:31.820,0:28:35.419
input stream is your keyboard basically

0:28:33.950,0:28:36.860
the input stream is your terminal and

0:28:35.419,0:28:38.929
whatever you type into your terminal is

0:28:36.860,0:28:40.610
going to end up into the program and it

0:28:38.929,0:28:42.049
has a default output stream which is

0:28:40.610,0:28:44.330
whenever the program prints something

0:28:42.049,0:28:46.279
it's gonna print to that stream and by

0:28:44.330,0:28:48.470
default that is also your terminal this

0:28:46.279,0:28:50.690
is why when I type echo hello it gets

0:28:48.470,0:28:54.200
printed back to my terminal but the

0:28:50.690,0:28:56.360
shell gives you a way to rewire these

0:28:54.200,0:28:59.120
streams to change where the input

0:28:56.360,0:29:00.980
output of a programmer pointed the way

0:28:59.120,0:29:06.200
the most straightforward way you do this

0:29:00.980,0:29:08.210
is using the angle bracket signs so you

0:29:06.200,0:29:11.570
can write something like this or you can

0:29:08.210,0:29:14.299
write something like this the left angle

0:29:11.570,0:29:16.340
bracket indicates rewire the input for

0:29:14.299,0:29:21.040
this program to be the contents of this

0:29:16.340,0:29:23.600
file and the end angle bracket means

0:29:21.040,0:29:27.559
rewire the output of the preceding

0:29:23.600,0:29:28.580
program into this file so let's look at

0:29:27.559,0:29:32.240
an example of what that would look like

0:29:28.580,0:29:34.280
if I do echo hello I can say I want that

0:29:32.240,0:29:36.710
context the content to be stored in a

0:29:34.280,0:29:39.049
file called hello dot text and because I

0:29:36.710,0:29:40.520
gave this is a relative path right this

0:29:39.049,0:29:42.980
will construct a file in the current

0:29:40.520,0:29:45.440
directory called hello text and at least

0:29:42.980,0:29:47.780
in theory its contents should be the

0:29:45.440,0:29:50.360
word hello so if I run this notice that

0:29:47.780,0:29:52.100
nothing got printed to my output the

0:29:50.360,0:29:52.700
previous time when I ran echo hello it

0:29:52.100,0:29:55.340
printed hello

0:29:52.700,0:29:57.799
now that hello is going gone into a file

0:29:55.340,0:30:00.610
called hello text and I can verify this

0:29:57.799,0:30:03.860
by using the program called cat so cat

0:30:00.610,0:30:07.280
prints the contents of a file so I can

0:30:03.860,0:30:11.059
do cat hello dot txt and there it shows

0:30:07.280,0:30:13.220
me hello but cat is a is also something

0:30:11.059,0:30:16.220
that supports this kind of wiring so I

0:30:13.220,0:30:17.990
can say cat which by default just prints

0:30:16.220,0:30:20.720
its input it just duplicates its input

0:30:17.990,0:30:23.809
to its output I can say I want you to

0:30:20.720,0:30:25.160
take your input from Hello text what

0:30:23.809,0:30:26.990
will happen in this case is that the

0:30:25.160,0:30:29.840
shell is going to open hello dot txt

0:30:26.990,0:30:32.540
take its contents and set that to be the

0:30:29.840,0:30:34.370
input of cat and then cat is going to

0:30:32.540,0:30:36.500
just print that to its output which

0:30:34.370,0:30:38.179
since I haven't rewired it is gonna be

0:30:36.500,0:30:41.870
my terminal so this will just print

0:30:38.179,0:30:43.549
hello to the output and I can use both

0:30:41.870,0:30:45.470
of these at the same time so for example

0:30:43.549,0:30:47.000
if I want to copy a file and I don't

0:30:45.470,0:30:51.500
want to use the CP command for some

0:30:47.000,0:30:54.470
reason I can do this and in this case

0:30:51.500,0:30:56.540
I'm telling the cat program nothing at

0:30:54.470,0:30:58.010
all I'm just saying do your normal thing

0:30:56.540,0:30:59.960
right the cat program does not know

0:30:58.010,0:31:02.150
anything about this redirection but I'm

0:30:59.960,0:31:04.190
telling the shell to use hello dot txt as

0:31:02.150,0:31:08.120
the input for cat and to write anything

0:31:04.190,0:31:09.470
that cat prints - hello - dot txt again

0:31:08.120,0:31:10.010
this prints nothing to my terminal

0:31:09.470,0:31:13.340
but if

0:31:10.010,0:31:15.620
cat hello to text I get the output as I

0:31:13.340,0:31:20.630
would have expected which is a copy of

0:31:15.620,0:31:23.390
the original file there is also a double

0:31:20.630,0:31:26.570
end bracket which is append instead of

0:31:23.390,0:31:27.380
just overwrite so you'll notice that I

0:31:26.570,0:31:29.870
if I do

0:31:27.380,0:31:32.300
cat hello dot txt - hello - dot txt

0:31:29.870,0:31:34.160
again and then I cat hello2 dot txt it

0:31:32.300,0:31:36.500
still just contains hello even though it

0:31:34.160,0:31:38.750
already contained hello if I switch that

0:31:36.500,0:31:41.090
to instead be a double end bracket it

0:31:38.750,0:31:45.890
means append and if I now cat that file

0:31:41.090,0:31:47.570
it has a hello twice these are pretty

0:31:45.890,0:31:49.850
straightforward they're usually just

0:31:47.570,0:31:51.590
ways to interact with files but where it

0:31:49.850,0:31:53.420
gets really interesting is an additional

0:31:51.590,0:31:56.150
operator the shell gives you called the

0:31:53.420,0:32:00.020
pipe character so pipe is just a

0:31:56.150,0:32:02.900
vertical bar and what pipe means is take

0:32:00.020,0:32:05.300
the output of the program to the left

0:32:02.900,0:32:09.650
and make it the input of the program to

0:32:05.300,0:32:13.940
the right right so what does this look

0:32:09.650,0:32:17.450
like well let's take the example of ls /

0:32:13.940,0:32:19.550
or ls dash l / this prints a bunch of

0:32:17.450,0:32:22.460
things let's say that I only wanted the

0:32:19.550,0:32:25.670
last line of this output well there's a

0:32:22.460,0:32:28.940
command called tail and tail prints the

0:32:25.670,0:32:32.420
last n lines of its input and I can do

0:32:28.940,0:32:34.520
-n1 so this is a flag called n you

0:32:32.420,0:32:36.890
can also use dash dash lines if you want

0:32:34.520,0:32:38.660
to use it as a longer option but in this

0:32:36.890,0:32:42.260
case this is saying just print the last

0:32:38.660,0:32:46.640
line and I can wire these together so I

0:32:42.260,0:32:50.840
can say ls dash l / pipe tail -n1

0:32:46.640,0:32:53.060
and notice here that ls does not know

0:32:50.840,0:32:55.340
about tail and tail does not know about

0:32:53.060,0:32:56.870
ls they are different programs and have

0:32:55.340,0:32:59.120
never been programmed to be compatible

0:32:56.870,0:33:00.650
with one another all they know how to do

0:32:59.120,0:33:02.900
is read from input and write to output

0:33:00.650,0:33:05.360
and then the pipe is what wires them

0:33:02.900,0:33:07.670
together and in this particular case I'm

0:33:05.360,0:33:09.380
saying I want the output of LS to be the

0:33:07.670,0:33:10.850
input to tail and then I want the output

0:33:09.380,0:33:12.140
of tail to just go to my terminal

0:33:10.850,0:33:14.240
because I haven't rewired it

0:33:12.140,0:33:16.730
I could also rewire this to say I want

0:33:14.240,0:33:18.770
the output to go to ls dot text and in this

0:33:16.730,0:33:20.990
case if I cat ls dot text I would get

0:33:18.770,0:33:22.640
the appropriate output and it turns out

0:33:20.990,0:33:21.815
you can do some really neat things with this

0:33:23.340,0:33:27.720
gonna cover this a lot more in the data

0:33:25.110,0:33:30.720
wrangling lecture there will be in like

0:33:27.720,0:33:32.490
four days or something on the kind of

0:33:30.720,0:33:36.060
fancy stuff you can do when you start

0:33:32.490,0:33:37.560
building more advanced pipelines one to

0:33:36.060,0:33:42.300
give you one example we can do something

0:33:37.560,0:33:46.320
like curl - -head --silent google.com

0:33:42.300,0:33:48.870
so just to show you what that looks

0:33:46.320,0:33:52.680
like this gives me all the HTTP headers

0:33:48.870,0:33:56.520
for accessing google.com and I can pipe

0:33:52.680,0:34:01.260
that to grep a - like a --ignore-case

0:33:56.520,0:34:04.230
or just -i if I want content

0:34:01.260,0:34:06.120
length so this is gonna print the

0:34:04.230,0:34:07.500
content length header, grep is a program

0:34:06.120,0:34:09.090
that we'll talk about later they'll let

0:34:07.500,0:34:12.660
you search in an input stream for a

0:34:09.090,0:34:15.560
given keyword we can pipe that through

0:34:12.660,0:34:20.190
say the cut command which takes a

0:34:15.560,0:34:22.260
delimiter set that to be space and I

0:34:20.190,0:34:24.420
want the second field and this prints

0:34:22.260,0:34:25.950
just the content length this is sort of

0:34:24.420,0:34:28.380
a silly example right like this just

0:34:25.950,0:34:30.180
lets you extract the content length in

0:34:28.380,0:34:32.700
bytes of google.com from the command

0:34:30.180,0:34:34.740
line it's not a very useful thing to do

0:34:32.700,0:34:36.300
but you can see how by chaining these

0:34:34.740,0:34:38.330
together you can achieve a bunch of

0:34:36.300,0:34:40.980
really interesting text manipulation

0:34:38.330,0:34:43.290
effects and it turns out pipes are not

0:34:40.980,0:34:45.330
just for textual data you can do this

0:34:43.290,0:34:47.850
for things like images as well you can

0:34:45.330,0:34:49.590
have a program that manipulates a binary

0:34:47.850,0:34:51.450
image on its input and writes a binary

0:34:49.590,0:34:53.400
image to its output and you can chain

0:34:51.450,0:34:54.840
them together in this way and we'll talk

0:34:53.400,0:34:57.000
about some of those kinds of examples

0:34:54.840,0:34:59.430
later on - you can even do this for

0:34:57.000,0:35:00.900
video if you want you can stream this is

0:34:59.430,0:35:02.940
for example a great way if you have a

0:35:00.900,0:35:05.790
chromecast at home you can stream a

0:35:02.940,0:35:07.920
video file like this by having the last

0:35:05.790,0:35:11.160
program in your pipe be a chromecast

0:35:07.920,0:35:13.050
send program so you stream a video file

0:35:11.160,0:35:19.140
into it and it streams or HTTP to your

0:35:13.050,0:35:20.370
chromecast we'll take we'll talk a lot

0:35:19.140,0:35:22.410
more about this in the data wrangling

0:35:20.370,0:35:25.110
lecture but there's one more thing that

0:35:22.410,0:35:27.800
I wanted to talk to you about about sort

0:35:25.110,0:35:30.390
of how to use the terminal and a more

0:35:27.800,0:35:31.920
interesting and perhaps more powerful

0:35:30.390,0:35:33.840
way that you might be used to and this

0:35:31.920,0:35:35.640
is perhaps even going to be interesting

0:35:33.840,0:35:37.720
for the ones of you who feel like you're

0:35:35.640,0:35:41.020
already comfortable with the term

0:35:37.720,0:35:43.030
but first we need to cover a important

0:35:41.020,0:35:44.890
topic when it comes to Linux systems and

0:35:43.030,0:35:47.620
Mac OS systems in particular which is

0:35:44.890,0:35:49.300
the notion of the root user the root

0:35:47.620,0:35:52.480
user is sort of like the administrator

0:35:49.300,0:35:55.000
user on Windows and it has user IDs zero

0:35:52.480,0:35:56.830
the root user is special because it is

0:35:55.000,0:35:59.680
allowed to do whatever it wants on your

0:35:56.830,0:36:01.540
system even if a file is like not

0:35:59.680,0:36:03.790
readable by anyone or if it's not

0:36:01.540,0:36:06.010
writable by anyone root can still access

0:36:03.790,0:36:09.000
that file root is sort of a super user

0:36:06.010,0:36:11.260
that gets to do whatever they want and

0:36:09.000,0:36:13.330
most of the time you will not be

0:36:11.260,0:36:15.550
operating as the super user you will not

0:36:13.330,0:36:17.350
be root you will be a user like John or

0:36:15.550,0:36:19.660
whatever your name is and that's going

0:36:17.350,0:36:21.370
to be the user you act with because if

0:36:19.660,0:36:23.470
you were operating your computer as the

0:36:21.370,0:36:24.700
root user at all times if you ran the

0:36:23.470,0:36:26.710
wrong program they could just completely

0:36:24.700,0:36:29.950
destroy your computer and you don't want

0:36:26.710,0:36:31.810
that right but every now and again you

0:36:29.950,0:36:34.450
want to do something that requires that

0:36:31.810,0:36:38.580
you are root usually for these cases you

0:36:34.450,0:36:42.790
will use a program called sudo su do or

0:36:38.580,0:36:44.740
do as su and su in this case is Super

0:36:42.790,0:36:46.590
User so this is a way to do the

0:36:44.740,0:36:49.750
following thing as the super user

0:36:46.590,0:36:51.490
usually the way sudo works is you write

0:36:49.750,0:36:53.020
sudo and then a command like you would

0:36:51.490,0:36:54.580
normally on your terminal and it will

0:36:53.020,0:36:56.230
just run that command as if you were

0:36:54.580,0:37:01.180
root as opposed to the user you actually

0:36:56.230,0:37:04.540
are where might you need something like

0:37:01.180,0:37:05.800
this well there is a special there are

0:37:04.540,0:37:07.510
many special file system on your

0:37:05.800,0:37:11.070
computer but in particular there's one

0:37:07.510,0:37:14.800
called sysfs if you CD to slash sys

0:37:11.070,0:37:17.320
this is a whole new world this file

0:37:14.800,0:37:19.720
system is are not actually files on your

0:37:17.320,0:37:22.120
computer instead these are various

0:37:19.720,0:37:24.180
kernel parameters so the kernel is like

0:37:22.120,0:37:26.680
basically the the core of your computer

0:37:24.180,0:37:29.560
this is a way for you to access various

0:37:26.680,0:37:32.680
kernel parameters through what looks

0:37:29.560,0:37:35.950
like a file system you'll see here that

0:37:32.680,0:37:37.690
if I CD into class for example it has

0:37:35.950,0:37:39.880
directories for a bunch of different

0:37:37.690,0:37:43.750
types of devices that I can interact

0:37:39.880,0:37:47.920
with or various queues I can access or all

0:37:43.750,0:37:49.990
sorts of weird knobs internally and

0:37:47.920,0:37:50.410
because they're exposed as files it means

0:37:50.410,0:37:54.280
we can also use all the tools have been

0:37:52.030,0:37:57.579
using so far in order to manipulate them

0:37:54.280,0:38:01.420
one example of this is if you go into

0:37:57.579,0:38:02.440
sys class backlight so this backlight

0:38:01.420,0:38:04.180
directly and lets you configure the

0:38:02.440,0:38:06.760
backlight on your laptop if you have one

0:38:04.180,0:38:08.920
so I can CD in to intel backlight this

0:38:06.760,0:38:10.990
is an Intel laptop inside here you'll

0:38:08.920,0:38:12.760
see there's a file called brightness and

0:38:10.990,0:38:16.089
I can cat the brightness this is the

0:38:12.760,0:38:18.880
current brightness of my screen but not

0:38:16.089,0:38:21.460
only that I can modify this too in order

0:38:18.880,0:38:23.740
to change the brightness of my screen so

0:38:21.460,0:38:25.750
you might think that I could do let's

0:38:23.740,0:38:26.799
see what the max brightness is here okay

0:38:25.750,0:38:29.589
so it's currently set to the max

0:38:26.799,0:38:32.319
brightness you might imagine that I

0:38:29.589,0:38:35.410
could do something like if I do echo

0:38:32.319,0:38:39.010
let's do half or something

0:38:35.410,0:38:38.010
echo 500 to brightness

0:38:38.010,0:38:39.010
if I do this it says

0:38:39.010,0:38:43.089
permission denied I'm not allowed to

0:38:40.839,0:38:45.220
modify brightness because in order to

0:38:43.089,0:38:46.599
basically in order to change things in

0:38:45.220,0:38:48.460
the kernel you need to be the

0:38:46.599,0:38:50.619
administrator and you might imagine that

0:38:48.460,0:38:52.960
the way to solve this is to write sudo

0:38:50.619,0:38:55.779
echo 500 but I still get a permission

0:38:52.960,0:38:58.260
denied error but why is that it's

0:38:55.779,0:39:00.549
because as I mentioned before these

0:38:58.260,0:39:03.069
redirections of input and output is not

0:39:00.549,0:39:05.470
something the programs know about when

0:39:03.069,0:39:07.240
we piped Elison to tail tail did not

0:39:05.470,0:39:09.609
know about LS and LS did not know about

0:39:07.240,0:39:11.859
tail the pipe and the redirection was

0:39:09.609,0:39:14.079
set up by the shell so in this case

0:39:11.859,0:39:18.039
what's happening is I'm telling my shell

0:39:14.079,0:39:21.220
run the program sudo with the arguments

0:39:18.039,0:39:24.130
echo and 500 and send its output to the

0:39:21.220,0:39:25.930
file called brightness but the shell is

0:39:24.130,0:39:29.410
what is opening the brightness file it

0:39:25.930,0:39:32.380
is not the sudo program so in this case

0:39:29.410,0:39:33.789
the shell which is running as me tries

0:39:32.380,0:39:35.470
to open the brightness file for writing

0:39:33.789,0:39:37.079
and it's not allowed to do that and

0:39:35.470,0:39:39.779
therefore I get a permission down error

0:39:37.079,0:39:42.339
you might have seen this if you like

0:39:39.779,0:39:43.750
search for something end up on Stack

0:39:42.339,0:39:45.400
Overflow and it tells just run this

0:39:43.750,0:39:47.440
command and you'll see that it does

0:39:45.400,0:39:52.930
something like they give you

0:39:47.440,0:39:57.970
instructions like one two sis what's an

0:39:52.930,0:39:59.559
example net ipv4 for word for example

0:39:57.970,0:40:02.589
this is something you may have seen if

0:39:59.559,0:40:04.240
you're setting up a firewall and this

0:40:02.589,0:40:05.680
command is intended to work

0:40:04.240,0:40:08.200
because this little pound symbol

0:40:05.680,0:40:09.640
indicates run this as root this is

0:40:08.200,0:40:11.170
something that is very rarely explained

0:40:09.640,0:40:12.970
but that is what the pound symbol means

0:40:11.170,0:40:15.099
you'll see on my prompt there's a dollar

0:40:12.970,0:40:17.710
symbol instead and the dollar indicates

0:40:15.099,0:40:18.819
you are not running as root so the

0:40:17.710,0:40:22.270
question is how do I get around this

0:40:18.819,0:40:24.690
well I could switch into a root terminal

0:40:22.270,0:40:27.369
so one way to do this is to run sudo su

0:40:24.690,0:40:32.140
sudo su is saying run the following

0:40:27.369,0:40:34.329
command s root and su is a complicated

0:40:32.140,0:40:37.290
command that effectively gets you a

0:40:34.329,0:40:40.599
shell as the super user so if I do this

0:40:37.290,0:40:42.010
type of password then now you'll see

0:40:40.599,0:40:44.530
that the username at the beginning

0:40:42.010,0:40:47.109
changed from jon to root and the prompt

0:40:44.530,0:40:49.390
changed from a dollar to a pound if I

0:40:47.109,0:40:52.240
now I come in to that file if I do echo

0:40:49.390,0:40:54.010
500 to brightness my screen got a little

0:40:52.240,0:40:57.040
dimmer but you can't see it you just

0:40:54.010,0:40:58.990
have to trust me and now I didn't get an

0:40:57.040,0:41:01.630
error and this is because the shell is

0:40:58.990,0:41:04.540
now running as root it is not running as

0:41:01.630,0:41:07.359
Jon and the root user is allowed to open

0:41:04.540,0:41:09.760
this file but given our knowledge that

0:41:07.359,0:41:11.349
we have of the terminal now there's

0:41:09.760,0:41:13.720
actually a way for us to do this without

0:41:11.349,0:41:19.119
having to drop to a root shell and that

0:41:13.720,0:41:22.990
is as follows that's I guess restore it

0:41:19.119,0:41:26.589
to 1060 so do you see why this is

0:41:22.990,0:41:29.020
different here I'm telling my shell to

0:41:26.589,0:41:31.270
run the echo 1060 command which is gonna

0:41:29.020,0:41:33.369
echo 1060 and I'm telling it to run the

0:41:31.270,0:41:35.890
sudo tee brightness command and I'm

0:41:33.369,0:41:39.160
telling you to send the output of echo

0:41:35.890,0:41:40.540
into sudo tee in order to understand this

0:41:39.160,0:41:43.450
you need to know what the tee command does

0:41:40.540,0:41:47.079
the tee command takes its input and writes

0:41:43.450,0:41:49.540
it to a file but also to standard out so

0:41:47.079,0:41:52.329
tee is a convenient way if you have say a

0:41:49.540,0:41:54.160
log file that you want to like send to a

0:41:52.329,0:41:56.230
file to store for later but you also

0:41:54.160,0:41:58.059
want to see it to yourself then you can

0:41:56.230,0:41:59.770
pipe it through tee give it the name of a

0:41:58.059,0:42:01.809
file and it will write whatever its

0:41:59.770,0:42:04.270
input is both to that file and to your

0:42:01.809,0:42:07.630
screen and here I'm taking advantage of

0:42:04.270,0:42:09.940
that program I'm saying run tee as route

0:42:07.630,0:42:12.970
and have tee right into the brightness

0:42:09.940,0:42:14.380
file and so in this case the tee program

0:42:12.970,0:42:16.150
which is what is opening the brightness

0:42:14.380,0:42:17.370
file is running as root and so it is

0:42:16.150,0:42:20.190
allowed to do

0:42:17.370,0:42:21.390
if I run this it will now again you

0:42:20.190,0:42:23.850
can't see but the brightness and I've

0:42:21.390,0:42:25.770
been turned on by a laptop and I don't

0:42:23.850,0:42:27.390
get any errors and I never had to drop

0:42:25.770,0:42:30.930
into a root shell and run commands there

0:42:27.390,0:42:32.160
which can often be somewhat dangerous if

0:42:30.930,0:42:33.450
you want to explore this filesystem a

0:42:32.160,0:42:35.940
little bit more there's a lot of

0:42:33.450,0:42:39.450
interesting stuff in here if you just

0:42:35.940,0:42:41.430
sort of start browsing around you can

0:42:39.450,0:42:42.930
find all sorts of fun things so for

0:42:41.430,0:42:45.090
example we noticed that there was a fun

0:42:42.930,0:42:48.540
brightness command here I wonder what

0:42:45.090,0:42:49.980
other kinds of brightness I can set so I

0:42:48.540,0:42:51.860
can use the find command which we will

0:42:49.980,0:42:56.000
also talk about in a coming lecture I

0:42:51.860,0:42:58.860
wouldn't look on any file whose name

0:42:56.000,0:43:01.890
it's a little like brightness in the

0:42:58.860,0:43:05.070
current directory that's unhelpful maybe

0:43:01.890,0:43:08.850
they're not files did I misspell

0:43:05.070,0:43:17.010
brightness yeah why is it being annoying

0:43:08.850,0:43:20.460
Oh apparently it does not want to search

0:43:17.010,0:43:23.910
for brightness for me how well luckily

0:43:20.460,0:43:27.480
for you I know of one already handy that

0:43:23.910,0:43:30.090
there is a subdirectory called LEDs and

0:43:27.480,0:43:32.400
LEDs have brightness too what kind of

0:43:30.090,0:43:36.960
LEDs are there ooh lots of things for

0:43:32.400,0:43:38.280
example the scroll lock led now most of

0:43:36.960,0:43:40.290
you probably don't know what the scroll

0:43:38.280,0:43:42.780
lock LED is or much less what scroll

0:43:40.290,0:43:45.770
lock is you might have seen a key on

0:43:42.780,0:43:47.670
your keyboard neighbor named scroll lock

0:43:45.770,0:43:49.650
basically no one knows what it means

0:43:47.670,0:43:51.750
anymore no one really uses it for

0:43:49.650,0:43:55.680
anything it's mostly just a dead key and

0:43:51.750,0:43:57.240
also a dead LED what if you wanted to

0:43:55.680,0:43:59.220
configure it so that every time you get

0:43:57.240,0:44:00.960
email your scroll lock LED lights up

0:43:59.220,0:44:03.270
because there's no other reason why it

0:44:00.960,0:44:06.000
would light up well if we seed you into

0:44:03.270,0:44:08.130
this particular directory that has a

0:44:06.000,0:44:12.320
brightness place and it's set to zero

0:44:08.130,0:44:12.320
well what happens if I write one into it

0:44:12.590,0:44:17.220
you probably should not just be writing

0:44:15.330,0:44:18.720
random numbers into random files in this

0:44:17.220,0:44:20.310
directory because you are affecting your

0:44:18.720,0:44:22.560
kernel directly like look up what the

0:44:20.310,0:44:24.240
files do in this particular case I have

0:44:22.560,0:44:28.050
warned safety goggles and I've done my

0:44:24.240,0:44:30.630
research so now you can't tell but on my

0:44:28.050,0:44:33.509
keyboard the scroll lock LED is now lit

0:44:30.630,0:44:35.400
so now if I wrote a program that like

0:44:33.509,0:44:37.829
did some checking of mail and stuff I

0:44:35.400,0:44:40.229
could have it at the end run a program

0:44:37.829,0:44:43.499
that echoes one into this file and now I

0:44:40.229,0:44:47.460
have a way for my led to my keyboard to

0:44:43.499,0:44:49.680
indicate when I've new email at this

0:44:47.460,0:44:50.940
point you should know roughly your way

0:44:49.680,0:44:54.269
around

0:44:50.940,0:44:56.249
the terminal around the shell and and

0:44:54.269,0:44:58.920
know enough to accomplish these basic

0:44:56.249,0:45:01.289
tasks at least in theory now you

0:44:58.920,0:45:02.819
shouldn't need to use like

0:45:01.289,0:45:03.420
point-and-click interfaces to find files

0:45:02.819,0:45:05.279
anymore

0:45:03.420,0:45:07.470
there's one remaining trick you might

0:45:05.279,0:45:10.529
need and that is the ability to open a

0:45:07.470,0:45:13.950
file so far I've only really given you

0:45:10.529,0:45:17.690
ways to find files but one thing you

0:45:13.950,0:45:21.420
should know about is missing semester

0:45:17.690,0:45:23.640
xdg-open this will probably only work

0:45:21.420,0:45:27.119
on Linux on Mac OS I think it's just

0:45:23.640,0:45:29.430
called open on Windows who knows

0:45:27.119,0:45:31.739
xdg-open you give the name of a file and

0:45:29.430,0:45:34.769
it will open it in the appropriate program

0:45:31.739,0:45:36.180
so if you open if you do xdg-open an

0:45:34.769,0:45:39.269
HTML file that will open your browser

0:45:36.180,0:45:41.039
and open that file and once you have

0:45:39.269,0:45:42.869
that program in theory you should no

0:45:41.039,0:45:45.059
longer need to open like a Finder window

0:45:42.869,0:45:46.799
ever again you might want to for other

0:45:45.059,0:45:48.180
reasons but in theory you can accomplish

0:45:46.799,0:45:50.789
at all using the tools that we've

0:45:48.180,0:45:53.849
learned today this might all seem

0:45:50.789,0:45:55.589
relatively basic for some of you but as

0:45:53.849,0:45:57.479
I mentioned this is sort of the ramp-up

0:45:55.589,0:45:59.460
period of now we all know how the shell

0:45:57.479,0:46:01.979
works and a lot of what we'll be doing

0:45:59.460,0:46:03.450
in future lectures is using this

0:46:01.979,0:46:07.019
knowledge to do really interesting

0:46:03.450,0:46:09.450
things using the shell that sort of this

0:46:07.019,0:46:10.979
is learning the the interface that we're

0:46:09.450,0:46:14.849
going to be using and so it's important

0:46:10.979,0:46:16.650
we all know it we're gonna talk a lot

0:46:14.849,0:46:18.269
more in the next lecture about how to

0:46:16.650,0:46:20.309
automate tasks like this how to write

0:46:18.269,0:46:22.140
scripts that run a bunch of programs for

0:46:20.309,0:46:24.390
you and have to do things like

0:46:22.140,0:46:26.700
conditionals and loops and stuff in your

0:46:24.390,0:46:29.009
terminal and do things like run a

0:46:26.700,0:46:30.390
program until it fails which can be

0:46:29.009,0:46:31.979
handy in classes where you want to run

0:46:30.390,0:46:35.369
something until your test suite fails

0:46:31.979,0:46:38.550
for example so that's the topic for next

0:46:35.369,0:46:39.900
week's lecture did you have a question

0:46:38.550,0:46:42.420
it's what you've been demoing this

0:46:39.900,0:46:49.770
assist directory that presumably will

0:46:42.420,0:46:52.530
only work if you're running that is a

0:46:49.770,0:46:55.440
good question I don't know whether the

0:46:52.530,0:46:57.570
windows subsystem for Linux will expose

0:46:55.440,0:46:59.280
the sis file system if it does it

0:46:57.570,0:47:03.180
probably only exposes a very small

0:46:59.280,0:47:08.490
number of things it might because there

0:47:03.180,0:47:10.320
are I don't know check it out

0:47:08.490,0:47:11.610
one thing you'll see is the lecture

0:47:10.320,0:47:14.370
notes for this lecture are already

0:47:11.610,0:47:16.770
online and at the very bottom of the

0:47:14.370,0:47:18.420
file there are a bunch of exercises some

0:47:16.770,0:47:20.190
of them are relatively easy some of them

0:47:18.420,0:47:22.560
are a little bit harder and what we

0:47:20.190,0:47:24.060
encourage you to do is to take a stab at

0:47:22.560,0:47:25.410
going through them if you know this

0:47:24.060,0:47:27.660
stuff already it should go really

0:47:25.410,0:47:29.400
quickly if you don't it might teach you

0:47:27.660,0:47:31.740
a bunch of things that you might not

0:47:29.400,0:47:33.150
realize you didn't know and for the

0:47:31.740,0:47:35.190
office hours that we're gonna do right

0:47:33.150,0:47:36.840
after this lecture we will happily help

0:47:35.190,0:47:38.160
you get through all of those or if there

0:47:36.840,0:47:39.540
are other commands and you learn in the

0:47:38.160,0:47:42.300
process you want to know how to use more

0:47:39.540,0:47:44.910
efficiently and then in next lecture

0:47:42.300,0:47:46.710
which is tomorrow will basically be

0:47:44.910,0:47:48.290
assuming that you know the kind of stuff

0:47:46.710,0:47:51.750
that the exercise is going to teach you

0:47:48.290,0:47:53.030
there's also a an email address on the

0:47:51.750,0:47:56.100
website where you can send us questions

0:47:53.030,0:47:58.860
if you think of something like after the

0:47:56.100,0:48:05.160
office hours are finished are there any

0:47:58.860,0:48:07.050
questions before we end today no no all

0:48:05.160,0:48:09.480
right well we will have office hours on

0:48:07.050,0:48:12.150
the ninth floor of the gates building of

0:48:09.480,0:48:15.830
building 32 in like five minutes

0:48:12.150,0:48:15.830
sweet see you there