Shell & Git

About this Document

This document contains the basic aspects of a workshop the student council offers to new cs students.

Reading this Document

CAVEAT: A common mistake or error in reasoning to avoid
Remark: More advanced knowledge
Unikn: A comment on university-specific aspects

Unikn: Getting Started

Internet Access

Make sure you have a working internet connection. On campus this means eduroam wifi. Follow the instructions here to get access. Ask "KIM Beratung" for help right at the entrance of the library if there are any issues.

Gaining internet access should be one of the first things you do on campus.

Access to University Servers

There are two relevant university servers for you:

Gitlab for git repos (more on that below)
titan07.inf.uni-konstanz.de for a working shell

CAVEAT: Are you not majoring in CS?

You are welcome to attend any of the workshops we offer. However, to fully gain access to the servers above you may need to send an email from your university mail account to syst@inf.uni-konstanz.de with the subject subscribe. This should give you access to the servers above within about five minutes.

SSH into titan

If you don't have an environment to play with the commands introduced below, you can use this server. It also comes with git preinstalled.

To access it we use ssh, a command to open a shell on a remote server. Using ssh differs a bit between operating systems, the most prominent ones are listed below. Please attend the workshop or "Schlüsselkompetenzen der Informatik" if you need help.

All Operating Systems: POP ID

For technical reasons you CANNOT login to the titan server with your usual "firstname.lastname" credentials. You have to find your pop_id and substitute it for pop_id in the commands listed for your operating system below.

Open https://www.kim.uni-konstanz.de/services/konten-und-passwoerter/
Click on Uni-Account
Login in with your "firstname.lastname" credentials
Unfold the "Mein Passwort" section
Copy the field called POP-Id, it should start with "pop" and end with some random numbers

Windows

Open cmd.exe
type ssh pop_id@titan07.inf.uni-konstanz.de
Use you university password to login, acknowledge the warnings you encounter (we can talk about what they mean after the workshop)

Max OsX

Open terminal application
type ssh pop_id@titan07.inf.uni-konstanz.de
Use you university password to login, acknowledge the warnings you encounter (we can talk about what they mean after the workshop)

Why use a shell?

Everything is a file!
Shell precisely/automatically modifies files
Basic shell and filesystem knowledge needed for git

Unikn: Being able to use shell and git is essential for "Programmierkurs 1" and "Schlüsselkompetenzen der Informatik".

Filesystem Structure

Tree
/ root and delimiter between directories/files
. shorthand for current directory
.. shorthand for parent directory
./../../file.txt relative path
/home/user/homework.tex absolute path
.ssh hidden file

CAVEAT: Not the layout of bits on a drive.

Remark: Everything is a file - even a keyboard or microphone.

How do I interact with the filesystem?

ls list files in directory
pwd print working directory
cd PATH change directory to PATH
mkdir PATH create directory at PATH
mv SOURCE DEST move SOURCE to DESTINATION
cp SOURCE DEST copy SOURCE to DESTINATION
touch FILE create empty FILE
nano FILE edit file

General structure: command -flags -- path

How are ownership and permissions managed?

$ ls -la

What is this string in front of the actual filename?

drwx:rwx:rwx
User:Group:All Permissions to (r)ead, (w)rite and e(x)ecute files.

User and group are also listed.

CAVEAT: Directories should always be executable.

How do I interact with permissions?

chmod change the rwx bits
chown change ownership of a file

CAVEAT: root can access everything / information is physically on disk.

How do I find the precise options for chmod and chown?

man [chmod|chown]
Generalization: man word (sometimes number before word, see man man)
Programs might have --help/-h options, sometimes info program
Search engine or LLM

Spoiler: [chmod|chown] is a regular expression.

Why should I use git for version control?

Versions of text
Collaboration on text

          /<-o
o<-o<-o<-o    \<-o<-o<-o<-o
          \<-o<-o/

o: commit <: reference to previous commit

How should I use git?

How do I create my first repository?

$ git init foo # initialize foo as a git repository
$ cd foo # move to foo
$ git config user.name "Foo BarBaz" # tell git your name
$ git config user.email foo@barbaz.com # tell git your email
$ nano README.md # start a project with a good README
$ git add README.md # tell git to care about the file
$ # you will need git stage before later commits
$ git commit -m "Add README" # Make your first commit

CAVEAT: Older git versions create a default branch called master instead of the more modern main on startup, but usually display a warning, when they do so. You can just carefully follow those instructions to rename master to main so that you don't get cryptic errors when you try to push to a remote that is initialized to main.

Remark: $ user prompt, # root prompt/comment

What if my friend has already created a repository and published it on the web?

$ git clone URL

How would I publish my work?

$ git remote add origin URL # tell git the url for the remote named origin
$ git push origin main # tell git to push the current branch to origin/main
$ git pull origin main # tell git to pull the changes from origin/main

Unikn: You can create your own git remote on the university gitlab. To avoid confusion, explicitely uncheck the "Initialize repository with README" box when creating a repository in the web interface.

Unikn Remark: If you are part of non-personal namespaces, take care to select the correct one for your repository.

I forgot where I left off, how do I orient myself?

$ git status
$ git log

How do I commit with style?

Imperative mood sentence, reference issue number if relevant
THIS LINE IS BLANK
- bulleted list of relevant information
- https://maybe.a.link

What should I commit?

JUST code & raw documentation
No binaries (a few images for a website are fine)

Remark: In the rare case of having to check in binaries, use git lfs.

I heard scary stories about conflicts?!

Push and pull to avoid, freshman debugging algorithm otherwise

CAVEAT: How do I stop myself from accidentally committing things?

Create .gitignore and enter the files
- Use the freshman debugging algorithm for details

The Freshman Debugging Algorithm

Read carefully! (your problem, the command you tried, the result you got)
Collect more information!
- ls, pwd, --help, man
- git status/log
- lecture slides
- next exercise on the sheet
Can you combine concepts?
Query a search engine or LLM with the error code or problem description. (CAVEAT: plagiarism!)
Ask via Discord/PZ809
Love it at least a little!