--- title: Git Gud author: Floris van den Bosch date: February 26, 2024 theme: dracula slideNumber: \'c/t\' --- # What is Git? ![](images/Git-Logo-White.png){width=25%} > - **_version control system_** (VCS) > - used on the **_command line_** > - **_Distributed_** version control --- ## Version Control System (VCS) manage changes made to collections of information
**Examples** - editions in books - revisions of technical standards - software versions --- ## Local VCS ::::: columns ::: column All version of your project are on your local PC ::: ::: column ![local VCS](images/local.png) ::: ::::: --- ## Centralized VCS ::::: columns ::: column All versions are on a server
Easy to manage, but has a single point of failure ::: ::: column ![centralized VCS](images/centralized.png) ::: ::::: --- ## Distributed VCS ::::: columns ::: column Everyone has a copy of the project.
This allows for more flexible setups. ::: ::: column ![distributed VCS](images/distributed.png){width=50%} ::: ::::: # Why use Git? --- ## Improve project management > 1. As lab journal for your scripts > 2. Identify when bugs are introduced > 3. Share and collaborate on projects --- ## Git works offline - Make and store changes offline - Project history is stored offline - Only need a connection when sharing --- # Git basics --- ## New/Existing project `git init` This creates the `.git` subdirectory that stores all versions We now have a git repository! --- ### example {.example} We create a new game based on werewolves and quantum mechanics ```shell $ mkdir quantumwerewolf $ cd quantumwerewolf $ git init ``` --- ## Copy a project `git clone ` The project is copied into the current directory --- ### example {.example} We clone a game about werewolves and quantum mechanics ```shell $ git clone https://github.com/ProodjePindakaas/Quantum-Werewolf.git $ cd quantumwerewolf ``` --- ## Making changes --- ### We found a bug! ```python if answer.isdigit(): # <-- This is the problem i = int(answer) - 1 if i in range(self.player_count): answer = self.players[i] ``` --- ### Let's fix it ```python if answer.isdecimal(): # Now it works! i = int(answer) - 1 if i in range(self.player_count): answer = self.players[i] ``` --- ### Staging the fix We now have made a change, but git has not **_recorded_** it yet We need to tell git which changes to record with `git add ` These changes are now **_staged_** --- ### Committing the fix Now the file is ready to be **_committed_** This will permanently add the changes to the file history --- ### Committing the fix `git commit` This will your text editor where you can describe the changes in this **_commit_** in detail. Or short description with the `-m` option `git commit -m "Fixed the bug"` --- ### Overview of file states ![Lifecycle of file statuses](images/lifecycle.png) --- ## Viewing changes `git status` View the current state of all files ```shell{.small} $ git status On branch main Your branch is up to date with 'origin/main'. Changes to be committed:  (use "git restore --staged ..." to unstage)        modified:   staged_file.txt Changes not staged for commit:  (use "git add ..." to update what will be committed)  (use "git restore ..." to discard changes in working directory)        modified:   modified_file.txt Untracked files:  (use "git add ..." to include in what will be committed)        new_file.txt ``` --- ### File changes See what you modified but have not staged with ```shell $ git diff ``` Or see what you have staged but not committed ```shell $ git diff --staged ``` --- #### Example ```diff diff --git a/quantumwerewolf/cli.py b/quantumwerewolf/cli.py index 6cfa32f..1a38216 100644 --- a/quantumwerewolf/cli.py +++ b/quantumwerewolf/cli.py @@ -70,7 +70,7 @@ class CliGame(Game):     def ask_player(self, query, invalid_players=[]):         answer = input(query + 'Name: ') -        if answer.isdigit(): +        if answer.isdecimal():             i = int(answer) - 1             if i in range(self.player_count):                 answer = self.players[i] ``` --- ### View history `git log` Get a summary of the commit history ```shell $ git log commit 5658af2ab70472d25bb47cf6a62468ec0b966ed3 (main) Author: Floris van den Bosch Date:   Wed Feb 28 11:06:31 2024 +0100    Fixed the bug ``` --- # Intermission ## `git init` ## `git clone` ## `git add` ## `git commit` ## `git status` ## `git diff` ## `git log` --- # Using branches --- ## Linear History Without branching our project history looks like this ![](images/basic-branching-1.png) _Note: the default branch may also be called `main`_ --- ## Creating a Branch `git branch ` this creates a new **_branch_** with the name `` Usually branches are created for a **_specific purpose_** - fixing a bug - a new feature --- ## Selecting a branch We can **_check out_** the new branch `git checkout ` Moves the **_HEAD_** to this branch and changes our local files accordingly. --- ### example We create new branch for the bug ```shell $ git branch iss53 $ git checkout iss53 ``` ![](images/basic-branching-2.png){width=80%} --- ### example With `git status` we can see on which branch we are ```shell $ git status On branch iss53 ``` --- ### example Now we make the changes as before and commit them with `git commit` ![](images/basic-branching-3.png){width=80%} --- ## Merging branches When a branch is done and tested we want to **_merge_** it into the main branch `git checkout ` `git merge ` --- ### example When all is we and tested we merge the fix for the issue. ```shell $ git checkout master $ git merge iss53 Updating f42c576..3a0874c Fast-forward quantumwerewolf/cli.py | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) ``` --- ### example ![](images/basic-branching-3a.png){width=80%} This we call a **_fast-forward_**, as the history is still linear --- ### diverging example We are working on two branches ![](images/basic-branching-4.png){width=80%} --- ### diverging example first we merge the hotfix into master ![](images/basic-branching-5.png){width=60%} This is a simple **_fast-forward_** --- ### diverging example The `hotfix` branch can now be deleted ![](images/basic-branching-6.png){width=80%} --- ### diverging example Finally, when the `iss53` branch is done we merge this into the `master` branch ![](images/basic-merging-2.png){width=80%} --- ## Conflicts If we alter the same line in the same file, we get a **_conflict_** --- ### example When a conflict occurs git does not make a new commit ```shell $ git merge iss53 Auto-merging example.txt CONFLICT (content): Merge conflict in quantumwerewolf/cli.py Automatic merge failed; fix conflicts and then commit the result. ``` --- ### example `git mergetool` This detects the conflict and lets you fix them in your favorite **_mergetool_** (e.g. vimdiff) After the manual merging we still need to **_commit_** the merge. --- ## Branching workflow ![](images/lr-branches-2.png){width=70%} - **_master_**: stable branch used for production - **_develop_**: semi-stable branch with finished features - _topical_: separate branch for each feature/bug --- ## Rebasing `git rebase ` An alternative to a merge (or fast-forward) is the **_rebase_** It fast-forwards the branching point of the branch _Best practice: avoid using rebases_ --- ### example We have a simple divergence ![](images/basic-rebase-1.png) --- ### example We could do a regular merge ```shell $ git checkout master $ git merge experiment ``` ![](images/basic-rebase-2.png) --- ### example Instead, we rebase the `experiment` to the `master` branch ```shell $ git checkout experiment $ git rebase master ``` ![](images/basic-rebase-3.png) --- ### example Now we move the `master` branch forward again ```shell $ git checkout master $ git merge experiment ``` ![](images/basic-rebase-4.png) --- # Working with Remotes --- ## Remotes A **_remote_** is a copy of the project's repository in another location **Examples** - on Github/Gitlab - a different machine in a network - a different folder on the same machine _Note: Using `git clone` automatically adds the remote **origin**_ --- ## Showing Remotes `git remote` This shows a list of current remotes `git remote -v` This shows the URLs for each remote --- ### example ```shell $ git clone https://github.com/ProodjePindakaas/Quantum-Werewolf.git $ cd quantumwerewolf $ git remote origin $ git remote -v origin  https://github.com/ProodjePindakaas/Quantum-Werewolf.git (fetch) origin  https://github.com/ProodjePindakaas/Quantum-Werewolf.git (push) ``` --- ## Pushing and Pulling `git fetch ` Gets the history on your remote `git push ` Sends and add your changes to the remote `git pull ` Retrieves and merges changes from the remote --- ### example Sending the bugfix to the remote (Github) ```shell $ git push -u origin iss53 ```
_Note: `-u` is needed as the `iss53` branch does not exist yet on the remote_ --- ### example Or get the fix from the remote ```shell $ git pull origin iss53 ```
_Note: this might be one situation to use **rebase** if you haven't pulled from the remote in a long while._ --- ## Adding remotes `git remote add ` Adds a new remote --- ### example We want to run the game on a cluster ```shell me@cluster $ git clone me@host:/path/to/repository me@host $ git remote add cluster me@cluster:/path/to/copy ``` Now we can push our program to the cluster! --- ## Hosting repositories **self-hosting options**: - bare repository with SHH/HTTPS - Self hosted web interface: GitWeb or Gitlab - Third party hosting: Github or Gitlab --- # Tips and Tricks --- ## gitignore Local files that you do not want to record: - temporary/cache files - Output files Declare files/folders you want git to ignore in `.gitignore` files _Hint: you can find premade `.gitignore` files in [github.com/github/gitignore](https://github.com/github/gitignore) for many programming languages_ --- ## Tags By default, git gives every version (commit) a hash to identify it `git tag ` Allows you to manually tag the current version (ex. `git tag v3.1.4`) You can also tag a previous commit with its hash `git tag ` --- ## stash We all make mistakes `git stash` Temporarily store your file modifications `git stash pop` Applies the stored changes to your current branch --- ## git tree The `git log` command shows a linear history by default `git log --oneline --graph --color --all --decorate` Shows the branches explicitly as 'timelines' --- ![](images/tree.png) --- ## Aliases You can alias command and options you often use `git config alias. ` such as `git config --global alias.tree 'log --oneline --graph --color --all --decorate'` Now we can just run `git tree`! --- ## rerere You may run into the same conflict numerous times `git config --global rerere.enabled true` Enabling ReReRe (Reuse Recorded Resolution) automatically applied your conflict resolutions to future occurences --- # Further reading Talk inspired by and with images from the book ProGit (Chacon, S., & Straub, B. Pro Git (Version 2) [Computer software]. https://github.com/progit/progit2) ![](images/cover.png){width=20%} https://git-scm.com/