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What is 391?

Learning objectives: collection of tools and topics not addressed in other classes that we think all CSE majors should know.

often called: the “missing semester” or “missing quarter” of a CS major
routinely cited (by alums) as one of the most helpful classes for future software engineers, data scientists, etc.
not a required class for the major or a prerequisite for any class;�the department offers it because students ask for it!

Bottom line: this class exists for your benefit!

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What is 391?

Logistically,

1-credit, credit/no-credit class, assessed on weekly homework

this class doesn’t impact your GPA but could have other implications

meets once a week (right now!)
uses:

cs.uw.edu/391 for course materials
Ed discussion board for online questions
Gradescope for submitting homework
Canvas for tracking progress

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Getting Help: Office Hours & Ed

Synchronous help: come to office hours!

can be: content questions, homework help, diving deeper, …
can also be: just do the homework and have someone around

Asynchronous help: post on the Ed Discussion board!

involves your solution code? make a private post.
feel free to answer each other’s questions!

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Getting Help: Everything Else

Discuss something that requires privacy? Feel free to sign up for a meeting.

In particular:

happy to work with you to navigate difficult personal situations
feel that you’re slipping? Let me know early!
not sure? feel free to ask (politely) – the worst I’ll say is no

Bottom line: please reach out!

Hello everyone! And welcome to CSE 391. My name is Trisha and I’m your TA. I took this course in Spring, not too long ago, so I just wanted to share a few words about mindset and striking balance.

The content of this course is extremely valuable and you’ll be acquiring and building skills that you’ll likely be using in the future, especially if you decide to pursue industry. That being said, it is a 1 credit credit/no credit course, and hence might not be your greatest priority.

Still, you’re likely taking this course because you have a genuine interest in the material, especially as it isn’t required.

Here’s what I ask of you. Do your best to stay engaged by attending weekly lectures, and completing the pre-class work and homework. Try to spend at least 3 hours really working on the homework. Please come to office hours if you need help. If you still can’t figure it out, it’s okay to take a break and come back later, whether that be the next day or much further down the line after you’ve submitted what you already have.

Treat this course as an exploration. Figure out what interests you more, and what interests you a little less. This is also a great opportunity to pick up self-driven learning. Learn how to ask good questions and find answers by perusing forums, coming to office hours, and scouring the man pages.

With that - all the best for the quarter! Come find me during OH if you have any questions!

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You get what you put in

I am not expecting this class to be your #1 priority in life! But in order to learn the material you will need to:

actively engage (watch the videos, come to class, do the HW)
plan & prioritize (submit the homeworks – no extensions!)

This class should not be a major source of stress/work but, there’s a ton of room to explore if you’re interested

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Operating Systems?

In the study of operating systems, a kernel is the program that manages software & hardware resources such as memory, networking, user input, etc.

Kevin’s laptop runs ChromeOS and his phone runs Android: both of these operating systems are based on the Linux kernel.

macOS and iOS are Unix-like but not based on the Linux kernel.

Windows is not Unix-like.

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Operating Systems?

What are the most common operating systems for…

personal computers?

~46% Android + ~19% iOS + ~5% macOS as of 2024 (StatCounter) – all Unix-like

server computers?

~88% Unix as of 2023 (W3 Techs)

supercomputers?

100% Linux out of the Top 500 fastest supercomputers since 2017 (Top500)

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Shell?

Despite differences, we often use computers via a desktop environment that helps you run apps and edit files using a mouse, keyboard, or touchscreen.

You’ve learned Java programming, which lets you compute new things. But it’s often uncomfortable writing Java programs that interact with files or run apps.

e.g. printing out the contents of a file can take 20 lines of Java code

The shell is a more direct way to write programs that interact with files.

e.g. the same task can be done in 1 line with the cat shell command

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Why Unix & Linux? (1/2)

Introduced many key ideas:

combining many little programs to solve one big problem
multiple users (with different permissions)
hierarchical file system (with recursive folders)
“everything is a file”
documentation included with software
also: shell scripts, coroutines, pipelines, regular expressions, …

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Why Unix & Linux? (2/2)

Widely impactful & influential:

easily the most deployed operating system in the world
now is realized as:

macOS & iOS (Unix -> BSD -> FreeBSD -> Darwin)
Android (uses Linux kernel)
Linux “distributions”, like Ubuntu, Debian, Arch, Red Hat, and Amazon Linux
(and integrated with Windows via WSL)

among other things, powers most web servers & cloud computing

Bottom line: almost impossible to “dodge” Linux as a programmer!

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the rest of this is a live demo :)

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Appendix: Commands

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Anatomy of a Command

Command line arguments surprisingly can be inconsistent, but for this class we’ll split them up into the command, optional flags, and optional arguments.

$ ls -al dir1

Command

Flags

Arguments

(Parameters)

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Command Line Arguments

Much like methods in Java (or other languages), commands take “arguments”.

For example, the following line lists all the files inside of the dir1 folder:

$ ls dir1

Here, we’ll say that dir1 is an argument to ls. Arguments are separated by spaces.

Flags are a special type of argument that typically change the behaviour of a program slightly; they are usually prepended with a - or –. For example,

$ ls -al dir1

Combines two flags: the -a flag (list hidden files) and the -l flag (use long-list format).

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Basic Shell Commands

command	description
pwd	Print current working directory
cd	Change working directory
ls	List files in working directory
man	Bring up manual for a command
exit	Log out of shell

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System Commands

command	description
clear	Clears all output from console
date	Output the system date
cal	Output a text calendar
uname	Print information about the current system

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Relative Directories

directory	description
.	References the working directory
..	References the parent of working directory
~username	username’s home directory
~/Desktop	Your desktop

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Unix File System Conventions

directory	description
/	Root directory that contains all directories
/bin	Applications/programs (i.e. binaries)
/dev	Hardware devices
/etc	Configuration files
/home	Contains user’s home directories
/proc	Running programs (processes)
/tmp, /var	Temporary files
/usr	Universal system resources

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Directory Commands

directory	description
ls	List files in working directory
pwd	Print current working directory
cd	Change working directory
mkdir	Make a new directory
rmdir	Remove the given directory (must be empty)

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File Commands

directory	description
cp	Copy a file
mv	Move a file (also used to rename files)
rm	Remove the given file
touch	Create empty file, or change time-modified

Warning: the above commands do not ask for confirmation. �Be careful when moving, copying, or deleting files!�(the man pages have flags that prevent this behaviour!)

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Text Editors

command	description
nano	Very simple editor
vim	More advanced text-editor
emacs	More advanced text-editor

In many instances, you’ll be interacting with a Linux system only through a console – so a command-line text editor is necessary.

vim is the main text editor we will learn in this class.

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vim basics

Key stroke	description
:w	Write (save) the current file
:wq	Write (save) the current file and exit
:q!	Quit, ignoring all changes
i	Go into insert mode
Esc	Go back to normal mode
hjkl	Move cursor left, down, up, right
u	Undo last change
x	Delete character

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emacs basics

Key stroke	description
C-x C-f	Read a file into emacs
C-x C-s	Save a file to disk
C-x C-c	Exit emacs
C-s	Search forward
C-r	Search backwards
C-v	Scroll to next screen
M-v	Scroll to previous screen
C-x u	Undo

C = control key

M = alt/meta key