2020 beta version

assets/branch-ff.drawio

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assets/branch-noff.drawio

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assets/branch-noff.svg

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content.md

-## Di cosa parliamo oggi?
-![](assets/git_fire.png)
-
----
-
-## ATTENZIONE
-
-Tutti i comandi trattati in queste slide possono modificare in modo permanente
-il repo git.  
-
-State Attenti  
-(Good news: git non cancella mai in modo implicito informazioni)
-
-----
-
-### Internals di Git
-
----
-
-![](assets/git_internals.png)
-
----
-
-### tl;dr
-
-* I *commit* sono oggetti con un puntatore al padre ed un puntatore ad un
-"pacchetto di file"
-* I pacchetti file sono compressi e contengono lo stato integrale del repo al
-momento del commit
-* un *tag* è un puntatore ad un commit
-* un *branch* è un tag che si muove in avanti ogni volta che si esegue un commit
-* `HEAD` punta al branch corrente
-
-(la questione è leggermente piu complicata, vedi [qui](https://git-scm.com/book/en/v2/Git-Internals-Plumbing-and-Porcelain) )
-
-----
-
-## git reset
-
----
-
-### `git reset <mode> <commit>`
-`git reset` permette di spostare `HEAD` a `<commit>`
-Le mode comuni sono:
-* `--soft`: sposta l'`HEAD`
-* `--mixed` (default): sposta l'`HEAD` e resetta l'index
-* `--hard`: sposta l'`HEAD` e cancella tutti i cambiamenti successivi
-
-----
-
-## git rebase
-Il ritorno
-
----
-
-### Rebase come strumento correttivo
-
-`git rebase -i <commit fine>`
-
-Operazioni:
-* reword: permette di cambiare il messaggio di commit
-* edit: permette di modificare i file
-* squash: "comprime" il commit con il precedente
-* drop: elimina il commit
-
-----
-
-## git gc
-
-![](assets/mop.png)
-
----
-
-Che succede?
-```
-git reset --soft HEAD~1
-<modifichiamo file>
-git commit
-```
-
----
-
-Come fare se volete cancellare i file *subito*
-```
-git reflog expire --expire-unreachable=now
-```
-
-----
-
-Ok, ma se voglio fare modifiche **grosse**?
-
----
-
-## reset, rebase
-
-![](assets/exc.jpg)
-
----
-
-## filter-branch
-
-<img src="assets/b288.jpg" style="width: 100%;max-width: 100%"></img>
-
----
-
-## git filter-branch --index-filter
-
-permette di eseguire cambiamenti solo all'index  
-(ovvero si possono eseguire solo comandi `git`)
-
----
-
-## git filter-branch --tree-filter
-
-si possono eseguire una serie di comandi arbitrari sul working tree  
-(è molto piu lento dato che c'è da fare il checkout per ogni commit)
-
-----
-
-# Domande?

index.html

@@ -97,9 +97,9 @@
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 		<section data-charset="utf-8"
 		         data-markdown="./slides/content.md"
-		         data-separator="^\r?\n---\r?\n$"
+		         data-separator="^\r?\n----\r?\n$"
 		         data-separator-notes="^Notes:"
-		         data-separator-vertical="^\r?\n----\r?\n$">
+		         data-separator-vertical="^\r?\n---\r?\n$">
 		</section>
 		<section data-external-replace="./slides/outro.html"></section>
 	</div>

slides/content.md

-# Intro e outro dentro l'HTML
+## What we will talk about today
 
-Il markdown contiene solo il contenuto.
+* Changing past git commits
+* Rewriting git history
+* Deleting files permanently in git
 
-Di base si possono fare le slide anche in HTML se si vogliono animazioni buffe.
+### tl;dr
+<img src="assets/doctor.png" style="max-height: 40%" />
+
+---
+
+## Warning
+
+All the commands in this presentation modify the git
+history in one way or another, this can lead to
+problems on shared projects and/or data loss.
 
 ----
 
-This is a long dash -- made of two little dashes (`--`).
+# Git Internals
+### I promise it will be short
+
+---
+
+## Diff
+
+A diff describes a change in a textual file
+
+```diff
+--- foo.txt     2020-03-22 15:01:25.425435217 +0100
++++ foo_2.txt   2020-03-22 15:01:43.028767920 +0100
+@@ -1 +1 @@
+-foo
++bar
+```
+
+It is the basic building block of every VCS
+
+---
+
+## Commit
+
+The **commit** is the building block of a git history  
+It is composed of:
+* An unique sha1 hash (compulsory)
+* A commit message
+* One (or more) father sha1s
+* None or more file diffs
+
+Generally a commit represents a 'snapshot' of all the project files
+
+---
+
+## Branches and Tags
+
+* **Branches** and **Tags** are both pointers to a specific commit (sha1)
+* Branches 'move' forward when you **`git commit`**, tags don't
+* **HEAD** is a special pointer that points to the curretly checked out branch 
+
+---
+
+![](assets/git_internals.png)
+
+---
 
-This dash is even longer --- and it is made of three little dashes (`---`).
+## Remotes
 
-"Quoting" is fun and easy. `"`Plain quoting`"` is ugly.
+A **remote** in git is another git repository  
+Generally this means your repo on github/gitlab/gitea/etc.  
+**origin** is the name of the remote when you `git clone`  
+(es. [https://github.com/torvals/linux]() )
+
+---
+
+## More on branches
+
+There are 2 types of branches:
+* Local branches (es. **master**)
+* Remote branches (es. **origin/master**)
+A local branch can __track__ a remote branch, which means that
+* **push**es from the local branch will go to the tracked remote branch
+* **pull**s will be merged to the tracking branch
+By default when you `git clone` git sets up the `master` branch to track `origin/master`
+
+---
+
+## Merges and fast-forwardability
+
+![](assets/branch-ff.svg)
+
+##### vs.
+
+![](assets/branch-noff.svg)
+
+---
+
+We say that a branch A is fast-forwardable w.r.t. branch B iff
+there is no bifurcation between A and B.  
+Why is this important?
+* A merge of a fast-forwardable branch always succeeds (just move B to point to A)
+* **git pull** and **git push** do not break only on fast forwardable branches (e.g. _master_ and _origin/master_)
+
+---
+
+## Forcing a push on a non-ff branch
+
+If you have a branch that has diverged, you need to use **`git push --force`**  
+Note that once you do this, every person that has cloned your repo will need
+to **`git pull --force`** and probably come to your house with torch and pitchfork.  
+**tl;dr `git push --force` responsibly**
 
 ----
 
-# Heading level 1
+# Ok enough theory
 
-## Heading level 2
+<img src="assets/bored.png" />
 
-### Heading level 3
+---
 
-#### Heading level 4
+## Time to break a git repo!
 
-There are **no** more heading levels.
+<img src="assets/explosion.gif" style="max-height: 50%" />
 
 ----
 
-<x-section-title>This is a section title</x-section-title>
+## amending commits
+![](assets/chisel.png)
+
+---
 
-If you want the section title in the top-right cornet
-you can add **&lt;x-section-title&gt;title&lt;/x-section-title&gt;** in the slide
+How many times happened that you `git commit`ed and then realized that:
+* There were files to include
+* You made a typo in your code
+* You broke your tests
+
+**` git commit --amend `** is the perfect tool for these situations
+
+---
+
+```bash
+# Add the missing files
+$ git add missing.txt
+# and then add it in the current commit
+$ git commit --amend
+```
 
 ----
 
-```python
-import sys
+## Undoing a lot of commits at once
 
-x = 1 + 2
+![](assets/shovel.jpg)
 
-if x > 2:
-  pass
+---
+
+### git reset
+`git reset` allows us to move **HEAD** (our current branch) to **`<commit>`**  
+There are 3 modes:
+* `--soft`: simply move `HEAD` (this is also what happens in a ff)
+* `--mixed` (default): move `HEAD` and reset index (file is still present in the working directory)
+* `--hard`: move `HEAD` and reset index and working directory
+
+----
+
+## git gc
+
+![](assets/mop.png)
+
+---
+
+Let's say I run this
+```
+git reset --soft HEAD~1
+<make some changes>
+git commit
+```
+
+What happened to the data that was in the initial **HEAD**?
+
+---
+
+Why doesn't **`git gc`** remove the commit?
 
-try:
-    with open('/dev/null') as f:
-        pass
-except IOError:
-    raise Exception('Error!')
-finally:
-    sys.exit()
 ```
+git fsck --unreachable --dangling --no-reflogs
+git reflog expire --expire=now --all
+git gc --prune=now
+```
+
+----
+
+## Rebase
+
+![](assets/exc.jpg)
+
+---
+
+## Rebase on branches
+
+Rebase, in its simplest form does the following:
+1. given a branch, find at which commit history has diverged
+2. compute the diff for each commit past the split
+3. reapply each diff onto the current branch (conflicts apply)
+4. for each new diff applied make a new commit with the original message
+5. once all the commits are applied, delete the original branch
+
+---
+
+## Interactive Rebase
+Rebase can also be used to touch-up a commit history  
+
+**`git rebase -i <end commit>`**  
+
+Once run a file will be opened with __$EDITOR__
+Possible operations:
+* reword: change the commit message
+* edit: change the file just before they were committed
+* squash/fixup: apply the changes in this commit to the previous commit
+* drop: delete the commit entirely
+
+----
+
+# What if I need to change a lot of files?
+
+---
+
+## filter-branch
+
+<img src="assets/b288.jpg" style="width: 100%;max-width: 100%"></img>
+
+---
+
+## git filter-branch --index-filter
+
+Allows to apply changes only to the index
+(basically only *git* commands are allowed)
+
+---
+
+## git filter-branch --tree-filter
+
+Allows us to run multiple commands on each commit  
+(it is much slower than index-filter since each individual commit
+needs to be checked out)
 
 ----
 
-- Do you remember bullet list?
-  ```python
-  bullet_list = ["Do you remember bullet list?"]
-  ```
-- You can also allign code to bullet lists!
-  ```python
-  bullet_list.append("You can also allign code to bullet lists!")
-  ```
-- It's not too hard!
-  ```python
-  if not hard:
-      bullet_list.append("It's not too hard!")
-  ```
\ No newline at end of file
+# Questions?

slides/intro.html

 <section class="intro">
-    <h1>Corsi Punto Croce 2018</h1>
-    <h2>Come fare gli orli</h2>
+    <h1>Corsi Git 2020</h1>
+    <h2>Disaster Recovery</h2>
 
     <img src="./poul/img/logo-text-white.svg"/>
 
-    <p>Autore &lt;email@email.com&gt;</p>
-</section>
\ No newline at end of file
+    <p>Giacomo Vercesi &lt;jackv@poul.org&gt;</p>
+</section>

slides/outro.html

@@ -3,9 +3,9 @@
 
     <img class="logo" src="./poul/img/logo-notext-white.svg"/>
 
-    <p>Rilasciato sotto licenza Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International</p>
+    <p>Released under Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International</p>
 
     <img class="cc" src="./poul/img/creativecommons-by-nc-sa.svg"/>
 
-    <p>Autore &lt;email@email.com&gt;</p>
-</section>
\ No newline at end of file
+    <p>Giacomo Vercesi &lt;jackv@poul.org&gt;</p>
+</section>