Unix Essentials Devin J. Pohly <djpohly@cse.psu.edu> CMPSC - - PowerPoint PPT Presentation

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Sep 17, 2023 111 likes •316 views

Systems and Internet i Infrastructure Security i Institute for Networking and Security Research Department of Computer Science and Engineering Pennsylvania State University, University Park, PA Unix Essentials Devin J. Pohly

SLIDE 1

CMPSC 311: Introduction to Systems Programming Page 1

Institute for Networking and Security Research Department of Computer Science and Engineering Pennsylvania State University, University Park, PA

Systems and Internet Infrastructure Security

i i

Unix Essentials

Devin J. Pohly <djpohly@cse.psu.edu>

SLIDE 2

Page 2 CMPSC 311: Introduction to Systems Programming

The Unix Philosophy

Write programs that do one thing and do it well.
Write programs to work together.
Write programs to handle text streams, because that

is a universal interface.

Doug McIlroy, Unix patriarch

SLIDE 3

Page 3 CMPSC 311: Introduction to Systems Programming

Why use the CLI?

Efficient and powerful
Easy to automate/script
Simple and reliable
Works even when

everything else is completely b0rked!

SLIDE 4

Page 4 CMPSC 311: Introduction to Systems Programming

CLI and the filesystem

Fairly typical structure
Everything under one root

directory, called “/”

Separate directory names

with additional slashes

To back out to the parent

directory, use “..”

Examples:

/usr/share/dict/words /usr/bin/../share/dict/words

These are called paths.

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Page 5 CMPSC 311: Introduction to Systems Programming

Top-level directories

Organized by the type of

files they contain

/usr: installed software
/usr/bin, /usr/lib, ...
/etc: configuration
/home: users’ own files
/dev: devices
/tmp: temporary files

SLIDE 6

Page 6 CMPSC 311: Introduction to Systems Programming

Navigating the filesystem

Current working directory
Default point of reference
Shown in prompt
Change directory: cd
cd /usr/share/dict
cd by itself takes you back

home

List files: ls
Special directory names
. means the working directory
.. means the parent directory

◾ So cd .. takes you up a level

SLIDE 7

Page 7 CMPSC 311: Introduction to Systems Programming

Practice

Find the configuration files for the APT package

manager.

View the list of sources using the less program.
Press q to quit less.

SLIDE 8

Page 8 CMPSC 311: Introduction to Systems Programming

Working with files

Copying files:
cp src dest
Moving/renaming files:
mv src dest
Removing files:
rm file
Creating/removing empty

directories:

mkdir newdir
rmdir dir

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Page 9 CMPSC 311: Introduction to Systems Programming

Getting help

Manual pages: man
Standard layout
man operator
man ascii
man man!
Man pages are full of info,

you just have to know where to look.

Keyword search: man k

‑

(Also Google)

SLIDE 10

Page 10 CMPSC 311: Introduction to Systems Programming

Common command syntax

Program: ls Arguments tell the program what to operate on: ls /home /usr Options modify program behavior: ls -l Options and arguments can be combined: ls -l -a /home ls -l --all /home ls -la /home

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Page 11 CMPSC 311: Introduction to Systems Programming

man practice

Find the command that prints a sequence of numbers.
Tell it to print the numbers 8 through 12.
Now tell it to pad the numbers with zeroes so everything

is the same length (08, 09, 10, 11, 12).

Remember: man -k to search, man to view.

SLIDE 12

Page 12 CMPSC 311: Introduction to Systems Programming

Editing text files

Unix philosophy again:

text is important!

Configuration? Text files.
Scripting? Text files.
Programming? Text files.
Vim (and vi)
Does one thing and does

it well

Integrates nicely with
ther CLI tools like Make

SLIDE 13

Page 13 CMPSC 311: Introduction to Systems Programming

Vim setup

sudo apt-get install vim wget tiny.cc/311setup sh 311setup

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Page 14 CMPSC 311: Introduction to Systems Programming

Understanding Vim

Several different modes
Indicator in bottom-left

corner

Normal mode (default)
Navigate the file
Most operations except

typing text

When in doubt, Esc gets

you to Normal mode.

Insert mode
Typing text

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Page 15 CMPSC 311: Introduction to Systems Programming

Getting around in Vim

Avoid those arrow keys!
Moving: h, j, k, l
Paging: Ctrl f/b, Ctrl u/d

‑ ‑

Other keys work too
Searching: /
(Regular expressions)
Practice: edit

/etc/services

To quit without saving,

type :q! and press Enter in Normal mode.

h j k l

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Page 16 CMPSC 311: Introduction to Systems Programming

Making changes

Getting to Insert mode
i: insert at cursor
A: append to this line
o: open a line below this
O: open a line above this
Esc: back to Normal mode
Also worth knowing
u: undo
Ctrl-R: redo
Write and quit: :wq

SLIDE 17

Page 17 CMPSC 311: Introduction to Systems Programming

Salutations!

Change to your home directory
Open the file yo.c in Vim
Fix the program by adding

#include <stdio.h>

at the top (hint: open a line above)

Write and quit: :wq
Shortcuts: ZZ to save and quit, ZQ to quit without saving.

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Page 18 CMPSC 311: Introduction to Systems Programming

Compile and run

Run the compiler:

gcc -o yo yo.c

Execute the program:

./yo

Edit it again
Delete a printf line by

moving to it and pressing dd.

Now add another printf

by using the o command.

Save, quit, compile, run!

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Page 19 CMPSC 311: Introduction to Systems Programming

Basic shell scripting

Eventually you’ll get tired
f repeatedly typing:

gcc -o yo yo.c ./yo

Shell script = list of

commands to run

Put these two lines in a

file called go.

Change yo.c, then run:

sh go

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Page 20 CMPSC 311: Introduction to Systems Programming

Learning Vim

Many, many features
Try everything, and find the
nes that work for you
:help

◾ :help user-manual

Use it on your own system!
GVim for Windows, MacVim

for Mac

Run vimtutor at the CLI
Simple, hands-on introduction
Do lessons 1.1–3.4 and learn

the commands and concepts