Git - The Incomplete Introduction

git – the incomplete introduction
git
the incomplete introduction
René Schwietzke, Xceptance, 2015
v 0.97

2git – the incomplete introduction
Please don't...
Please don't ask for any mapping of SVN to Git
commands. Git is different and you cannot simply
use the same approach and commands.
Of course you can, but people will hate you forever.

Some (de)motivation first
●
Most of things are borrowed
●
Command line only first
●
Yes, you can mess things up
●
Don't be scared!
●
Be scared and respect the tool!
●
Not every term will be introduced
●
Google is your friend
●
Go http://git-scm.com/ and use the book!
●
Share this deck, it is CC-BY-SA licensed

Why are we so... excited?
●
Subversion is ok – Git is better
●
Commit often, very often...
●
Everything is local
●
Everything is distributed
●
Cheap branching
●
Data assurance
●
Fast
●
Everything has a history... P.S That is going to be important later on
The swiss army knife – you just have to know how to use it.

What is that GIT/git/Git thing?
●
Distributed Version Control System (DVCS)
●
Open Source
●
Started by Linus T. to aid kernel development
●
Used by a lot of projects
●
Git is not GitHub!
●
Git is not Stash!
Git is a free and open source distributed version control system designed to handle
everything from small to very large projects with speed and efficiency.

Git takes care of...
●
Content: by protecting each commit with SHA-1
●
History: by keeping relations
●
Merges: by using the history
●
Speed: by using snapshots and not diffs

Distributed vs. Centralized
Centralized Distributed


 


How things are stored
●
Snapshots and not file differences

Lifetime phases of data
●
Untracked – data is not known to Git
●
Unmodified – you did nothing
●
Modified – you changed something
●
Staged – you prepared for a commit
●
Committed – you made changes permanent
●
Pushed – you shared your changes
You have to tell Git that you want a file to be included in the next
commit. Git is opt-in!
The thingy where Git keeps your soon to be committed data is called
the staging area.

Data assurance and commits
●
Git does not have a counter
●
Git has data assurance
●
Changes in the past will change anything from that
point in time
●
A commit knows its predecessors
●
A commit has a unique SHA-1
●
Any change to a commit changes the SHA-1
●
Any new SHA-1 is something new despite the
same content (see rebase)

What is a commit?
●
A commit is a snapshot of files
●
Keeps references to its parents
●
Has a unique SHA-1 over the content
Local ~$ git show --pretty=raw 28d88a4
commit 28d88a44d6640a7ab89aa9b0db0597e36b50c831
tree 55335193a182bc9e2850d00700ff482896f95c0f
parent bcbb62be834ca0abd4b81952e612bf64f57bedb2
author Kati Smith <kati@foobar.net> 1379449534 +0200
committer Kati Smith <kati@foobar.net> 1379449534 +0200
Fallback code added
Local ~$ git show --pretty=fuller 0da605d
commit 0da605df6974eaeef472355936b9fc15912a6211
Merge: a6c4011 28d88a4
...

What is a branch?
●
A branch is just a pointer to a commit that is the
branch head
●
A branch contains everything that can be reached
by following the parent relations
●
A branch is like a parallel universe
●
Each branch has a name
B
A

Get your hands gitty
We play with git

Get your hands gitty
●
Local repo first
●
Learn the basics
●
Clone a remote repo
●
Some magic around shared code
Local ~$ git –-version
git version 2.3.4

git init
●
Creates a new repository right here
●
Never ever play with .git subdirectory
Local ~$ mkdir mytest
Local ~$ cd mytest
Local ~mytest$ git init
Initialized empty Git repository in ~mytest/.git/
Local ~mytest$ ls -la
total 0
drwxrwxr-x 3 tfontane tfontane 60 Jul 27 20:56 .
drwxrwxr-x 7 tfontane tfontane 200 Jul 27 20:56 .git

git init
File Sys
git
HEAD
?

git config
●
Tell something about you
●
Git identifies you but does not authenticate!
●
Stash/GitLab/GitHub do the authentication
Local ~$ git config user.name "Rene Schwietzke"
Local ~$ git config user.email "emailme@foobar.com"
Local ~$ git config --global user.name "Rene Schwietzke"
Local ~$ git config --global user.email "emailme@foobar.com"

git status - add a little
●
Create a file and fill it
●
Check the status
●
git status is your friend!
Local ~mytest$ vi foo.txt
Local ~mytest$ git status
# On branch master
#
# Initial commit
#
# Untracked files:
# (use "git add <file>..." to include in what will be committed)
#
# foo.txt
nothing added to commit but untracked files present (use "git add" to
track)

Modified
File Sys
git
HEAD
?
foo.txt

git add / git status
●
Stage the file to make it known to git
●
Git will snapshot the file
●
Check the state
Local ~mytest$ git add foo.txt
# On branch master
#
# Initial commit
#
# Changes to be committed:
# (use "git rm --cached <file>..." to unstage)
#
# new file: foo.txt
#
Local ~mytest$ git add . # all recursive
Local ~mytest$ git add * # all in current dir

Staged
master
File Sys
git
HEAD
?
foo.txt
foo.txt

git commit – engrave it in stone
●
Make your changes permanent
●
Commits only what you staged
●
No commit comment – no fun!
Local ~mytest$ git commit -m “Just started”
[master (root-commit) c6a0313] Just started
1 file changed, 2 insertions(+)
create mode 100644 foo.txt
# On branch master
nothing to commit, working directory clean
Local ~mytest$

Committed
master
File Sys
git
HEAD
c6a0313
foo.txt

Play it again Sam!
master
File Sys
git
HEAD
c6a0313
foo.txt
64177f

git branch / git checkout
●
Cheap and fast
●
Your playground to try things, finish things, and
share things, all that without disturbing others
●
Use a branch, Luke!
Local ~mytest(master)$ git branch mybranch1; git checkout mybranch1
Local ~mytest(master)$ git checkout -b mybranch1
Switched to a new branch 'mybranch1'
Local ~mytest(mybranch1)$ git status
# On branch mybranch1
Local ~mytest(mybranch1)$ git branch
master
* mybranch1
Local ~mytest(mybranch1)$ git checkout master
Switched to branch 'master'
Local ~mytest(master)$ git checkout mybranch1
Switched to branch 'mybranch1'

Branch View
master git
HEAD
c6a0313 64177f
mybranch1
HEAD

Modify / Add / Commit
master git
c6a0313 64177f
mybranch1
HEAD
HEAD
7a1198e

Back to master and new file
master git
HEAD
c6a0313 64177f
mybranch1
7a1198e
HEAD
407084b

git rebase on mybranch1
●
Prepare mybranch1 for merge into master
●
Resolve conflicts in the branch
●
Rebasing means rewriting of history
Local ~mytest$ git checkout mybranch1
Local ~mytest$ git rebase master
First, rewinding head to replay your work on top of it...
Applying: Longer sentence
Local ~mytest$ git log --oneline --decorate
703e3f7 (HEAD, mybranch1) Longer sentence
407084b (master) First readme version
641771f Again
c6a0313 Just started

We rebased
master git
HEAD
c6a0313 64177f
mybranch1
7a1198e
HEAD
407084b
703e3f7

git merge into master
●
Get your changes into the master
●
Should run great because you rebased first
●
Git will remember that the branch was merged
●
Git will remember the content aka the SHA-1s
Local ~mytest$ git checkout master
Local ~mytest$ git merge mybranch1
Updating 407084b..703e3f7
Fast-forward
foo.txt | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
Local ~mytest$ git log --oneline --decorate
703e3f7 (HEAD, mybranch1, master) Longer sentence
407084b First readme version
641771f Again
c6a0313 Just started

We merged via fast-forward
master git
HEAD
c6a0313 64177f
mybranch1
407084b 703e3f7
HEAD

That was normal but not cool
●
We fast-forwarded and lost merge info
●
Fast-forward makes it look like a direct commit
●
Will retain all single commits and smuggle them
into the target branch
●
Hard to figure out what was going on
●
Use --no-ff all the time when merging
●
Fast-forwarding is great for rebasing but not for
merging (exceptions apply)

Prepare again
master git
HEAD
407084b
mybranch2
HEAD
703e3f7
750ba6b

Prevent fast-forwarding
●
Use --no-ff all the time
Local ~mytest$ git checkout master
Local ~mytest$ git merge --no-ff mybranch2
Merge made by the 'recursive' strategy.
lion.txt | 1 +
1 file changed, 1 insertion(+)
create mode 100644 lion.txt
Local ~mytest$ git log --oneline --decorate --graph
* f223150 (HEAD, master) Merge branch 'mybranch2'
|
| * 750ba6b (mybranch2) The new file
|/
* 703e3f7 (mybranch1) Longer sentence
* 407084b First readme version
* 641771f Again
* c6a0313 Just started

Perfect merge via --no-ff
master git
HEAD
407084b
mybranch2
HEAD
703e3f7
750ba6b
f223150

Remove merged branches
●
Always clean up never not continue
●
Merging means finishing up!
●
More reasons: see reverting a merge
Local ~mytest$ git branch -d mybranch1
Deleted branch mybranch1 (was 703e3f7).
Local ~mytest$ git branch -d mybranch2
Deleted branch mybranch2 (was 750ba6b).
Local ~mytest$ git log –-oneline –-decorate –-graph
* f223150 (HEAD, master) Merge branch 'mybranch2'
|
| * 750ba6b The new file
|/
* 703e3f7 Longer sentence
* 641771f Again

Clean up after merges
master git
407084b
HEAD
703e3f7
750ba6b
f223150

The small helpers
Other commands you might need

git rm – remove stuff
●
git rm removes and stages
●
Register already deleted files with git rm
Local ~mytest$ git rm lion.txt
rm 'lion.txt'
# On branch remove1
# (use "git reset HEAD <file>..." to unstage)
#
# deleted: lion.txt
#
Local ~mytest$ rm readme.txt
Local ~mytest$ git rm readme.txt

git mv – rename stuff
●
git mv renames/relocates and stages
●
Recommended but not required
●
git tracks content not files so it guesses external
moves based on content similarity
Local ~mytest$ git mv readme.txt README
# On branch remove1
#
# renamed: readme.text -> README
#
Local ~mytest$ git commit -m “Adjusted to GitHub style”
[remove1 72f240a] Adjusted to Github style
1 file changed, 0 insertions(+), 0 deletions(-)
rename readme.text => README (100%)

git diff – what changed?
●
To see changes locally: now vs. HEAD
Local ~mytest$ change a file, e.g. README
Local ~mytest$ git diff
diff --git a/README b/README
index a3a48b3..81db0bb 100644
--- a/README
+++ b/README
@@ -1 +1 @@
-My readme and it is more
+My readme and it is more.
Local ~mytest$ git diff --word-diff
diff --git a/README b/README
index a3a48b3..81db0bb 100644
--- a/README
+++ b/README
@@ -1 +1 @@
My readme and it is [-more-]{+more.+}
Local ~mytest$ git diff README
...

git diff – what changed?
●
To see changes of commits
Local ~mytest$ git log <you know the rest>
* 079aaab (HEAD, origin/master, master) master 3
* 7ba35ee master 2
* cad3fee master 1
Local ~mytest$ git show 079aaab
What changed with 079aaab
Local ~mytest$ git diff 7ba35ee
What changed since 7ba35ee aka the change introduced by 079aaab
Local ~mytest$ git diff 703e3f7 README
Same as before, but limited to a specific file
Local ~mytest$ git log --since=2.weeks readme.txt
List all commits that touched readme.txt in the last two weeks.
Local ~mytest$ git log --since=2.weeks -G Rene
Where 'Rene' was in the changes including removals in the last two weeks.
You can go nuts here. Google it when you need it. It is powerful and allows
basically everything possible to find and identify changes and problems.

git mergetool – conflict solver
● Solve conflicts during rebasing and merging
● Uses the configured tool of your choice
Local ~mytest$ git rebase origin/qa
Applying: Conflict
Using index info to reconstruct a base tree...
M qa/start.txt
Falling back to patching base and 3-way merge...
Auto-merging qa/start.txt
CONFLICT (content): Merge conflict in qa/start.txt
Failed to merge in the changes.
Patch failed at 0001 Conflict
The copy of the patch that failed is found in:
/tmp/learn_git/.git/rebase-apply/patch
When you have resolved this problem, run "git rebase --continue".
If you prefer to skip this patch, run "git rebase --skip" instead.
To check out the original branch and stop rebasing, run "git rebase –abort".
Local ~mytest$ git mergetool
Local ~mytest$ git rebase --continue

git cherry-pick – simply the best
● Rescue commits
● Preserves all data but the SHA-1 because of the
new predecessor
● Good for downstream hotfix merges
● Use to preserve pieces of a dead branch
Local ~mytest (master)$ git checkout -b kirsche
Local ~mytest (kirsche)$ git cherry-pick 56fe781
[tets b8c3f20] New readme file

Dealing with Oops!
The reason for version control

Forgot something? --amend
●
Changes the last commit (when not pushed!)
●
Removes old commit, creates new commit
Local ~mytest$ change two files
Local ~mytest$ git commit -m “Updated two files”
Local ~mytest$ git log --stat
* 5cb60ce (HEAD, master) Updated two files
| foobar.txt | 1 +
| 1 file changed, 1 insertion(+)
* 0da605d Merge branch 'oauth.fix'
Local ~mytest$ git add file2.txt
Local ~mytest$ git commit --amend -m “Really updated two files”
Local ~mytest$ git log --stat
* c3ae1b1 (HEAD, master) Really updated two files
| foobar.txt | 1 +
| readme.txt | 1 +
| 2 files changed, 2 insertions(+)
* 0da605d Merge branch 'oauth.fix'

Staged too much?
●
Remove from the staging area
●
Not very intuitive... sadly enough
Local ~mytest$ git add test.txt
# On branch master
#
# new file: test.txt
#
Local ~mytest$ git reset HEAD test.txt
# On branch master
# Untracked files:
# (use "git add <file>..." to include in what will be committed)
#
# test.txt
nothing added to commit but untracked files present (use "git add" to
track)

Get rid off the last commit
●
Kills the last commit without a trace
●
Of course, only when not shared yet
Local ~mytest$ git log
* 4db3017 (HEAD, master) Too much, oops
* a0a842d Fine 2
* 99ca82a Fine 1
Local ~mytest$ git reset HEAD~1
Unstaged changes after reset:
M readme.txt
* a0a842d (HEAD, master) Fine 2
* 99ca82a Fine 1

git revert – undo things I
●
Reverting means committing reversed content
●
Step 1: Identify hash aka revision
Local ~mytest$ git log --oneline --graph --decorate
* 01d9051 (HEAD, master) Cleaner now
|
| * 72f240a Adjusted to Github style
| * 5a9e51a Redundant file removed
|/
* f223150 Merge branch 'mybranch2'
|
| * 750ba6b The new file
|/
* 703e3f7 Longer sentence
* 641771f Again

git revert – revert a merge
●
Merges are reverted like any other commit
●
But when you continue to work on it and merge
later, it does not work as expected
●
Git does not track the content, but the commits
●
When commits are already in the tree, the next
merge with them again makes no difference aka
they are still reverted
●
Revert the revert in these cases first

Local ~mytest (master)$ git log
* 5169844 (HEAD, master) Foo is new
* 35a597f Merge branch 'test1'
|
| * 52212e1 A change in readme
|/
* bbd0c7b (origin/master) Readme 2
# identify predecessor to use
Local ~mytest (master)$ git show 35a597f
Merge: bbd0c7b 52212e1
Author: Peter Meier <r.schwietzke@xceptance2.net>
...
# revert 35a597f
Local ~mytest (master)$ git revert -m 1 35a597f
# create branch to continue
Local ~mytest (master)$ git checkout -b fix-it
# revert the revert in the branch to see original code
Local ~mytest (fix-it)$ git revert 42635ec
# fix all the bad stuff and merge
Local ~mytest (fix-it)$ edit, add, commit...
Local ~mytest (fix-it)$ git checkout master
Local ~mytest (master)$ git merge --no-ff fix-it
# clean up
Local ~mytest (master)$ git branch -d fix-it

Local ~mytest (master)$ git log
* 70e18de (HEAD, master) Merge branch 'fix-it', previously test1
|
| * d980ef0 Fixed the bad stuff
| * b8796e0 Revert of "Revert "Merge branch 'test1'""
|/
* 42635ec Revert "Merge branch 'test1'"
* 5169844 Foo is new
* 35a597f Merge branch 'test1'
|
| * 52212e1 A change in readme
|/
* bbd0c7b (origin/master) Readme 2
●
42635ec – revert in main branch
●
b8796e0 – revert of the revert to continue later
●
70e18de – second merge attempt including fix

git reset/checkout – trash it
●
Kill or revert all your uncommitted changes
# git rid off all changes
Local ~mytest$ change a file, e.g. README
Local ~mytest$ git reset --hard
HEAD is now at 25f967d ! The was the message.
# remove from staging area
Local ~mytest$ change a file
Local ~mytest$ git reset README
Unstaged changes after reset:
M README
# get README back to last commited state
Local ~mytest$ git checkout README
# On branch master

It is called branching,
not treeing
Do not build trees from your branches

Branches – important to know
● Remember, every commit has at least one parent
● So your branch is based on something
● If you merge your branch to a place you have not
started from, you get everything merged that is
not yet in... not just what you have touched
● Git makes sure that nothing is lost
● A branch is just a pointer!

Branches – the unexpected
?
B C
1 2
A E F
CD12
D
ZYXW

Branches – cherry-pick from red
1 2
1' 2'
Local (red)$ git checkout -b get-red-in
Switched to new branch 'get-red-in'
Local (get-red-in)$ git cherry-pick 1 2
Local (get-red-in)$ git checkout green
Switched to branch 'green'
Local (green)$ git merge --no-ff get-red-in -m “Cherry picked the red”
...
Local (green)$ git branch -d get-red-in

A small workflow
Just you and git. Local and simple.

Small and quick local workflow
●
Practice the workflow in your local world
Local (abranch)$ git checkout master
Switched to branch 'master'
Local (master)$ git checkout -b new-branch
Local (new-branch)$ edit and commit often
Local (new-branch)$ git rebase master
Local (new-branch)$ git checkout master
Local (master)$ git merge --no-ff new-branch -m “Cleaner now”
Removing lion.txt
readme.text => README | 0
lion.txt | 1 -
2 files changed, 1 deletion(-)
rename readme.text => README (100%)
delete mode 100644 lion.txt
Local (master)$ git branch -d new-branch

Let's go remote now
Play with others in the same sandbox

Let's go remote
● Every repository is a complete repo
● Except for unsynced changes with “friends”
● No obligation to use a remote
● More than one remote possible
● No obligation to upload (push) everything
● Only what you want to share
● Only what you have to protect

git clone – get a remote repo
Local ~mytest$ git clone
ssh://git@git0.foobar.net:7999/train/learn_git.git
Cloning into 'learn_git'...
remote: Counting objects: 192, done.
remote: Compressing objects: 100% (160/160), done.
remote: Total 192 (delta 78), reused 0 (delta 0)
Receiving objects: 100% (192/192), 20.35 KiB | 0 bytes/s, done.
Resolving deltas: 100% (78/78), done.
Checking connectivity... done
Local ~mytest$ cd learn_git
* master
Local ~mytest$ git remote --verbose
origin ssh://git@git0.foobar.net:7999/train/learn_git.git (fetch)
origin ssh://git@git0.foobar.net:7999/train/learn_git.git (push)
● Get a remote repo downloaded
● Git automatically sets up tracking

git fetch – get work from others
● Fetches data from remote
● Does not touch your work
Local ~mytest$ git fetch origin
remote: Counting objects: 7, done.
remote: Compressing objects: 100% (4/4), done.
remote: Total 4 (delta 2), reused 0 (delta 0)
Unpacking objects: 100% (4/4), done.
From ssh://git0.svc1.foobar.net:7999/train/learn_git
aa2e115..d85515d qa -> origin/qa
Local ~mytest$ git diff aa2e115..d85515d
diff --git a/qa/start.txt b/qa/start.txt
index 006f308..067ab29 100644
--- a/qa/start.txt
+++ b/qa/start.txt
@@ -1,3 +1,5 @@
This is beginning of a text.
It might continue.
Or it might now.
+I am remote.

git merge/rebase – pull it in
● Works like a local rebase or merge
● Picks the way that fits best
● Merge to make operation visible
● Rebase to just get you updated to latest
Local ~mytest$ git fetch origin
Local ~mytest$ git merge origin/qa
qa/start.txt | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
Local ~mytest$ git rebase origin/qa

git pull – fetch and merge
● Pull is fetch and merge in one command
● There is no --no-ff option, git picks the best way
● So prefer --rebase when content is unpushed
Local ~mytest$ git pull origin mybranch
From ssh://git0.foobar.net:7999/train/learn_git
* branch mybranch -> FETCH_HEAD
Updating 0d1c02a..974c00d
Fast-forward
qa/start.txt | 2 ++
1 file changed, 2 insertions(+)
Local ~mytest$ git pull --rebase origin mybranch

git push – deliver your work
● Deliver your work to a remote destination
● Nothing changes (commit hashes)
● DO NOT CROSS PUSH
Local ~mytest$ branch, edit, commit
Local ~mytest$ git push origin qa
Counting objects: 5, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (3/3), done.
Writing objects: 100% (4/4), 377 bytes | 0 bytes/s, done.
Total 4 (delta 1), reused 0 (delta 0)
To ssh://git@git0.foobar.net:7999/train/learn_git.git
* [new branch] qa -> qa
* 0743e1d (HEAD, origin/qa, qa) QA directory
* d0400d5 (origin/master, origin/HEAD, master) Merge pull request
#12...
...

git push – too slow and you fail
● Someone was faster
● You have to get the remote changes first
● Prefer rebase over merge, avoids ugly commit
Local ~mytest$ branch, edit, commit
Local ~mytest$ git push origin master
To ssh://git@gitlab.foobar.de/test/training.git
! [rejected] master -> master (fetch first)
error: failed to push some refs to
'ssh://git@gitlab.foobar.de/test/training.git'
hint: Updates were rejected because the remote contains work that you
do not have locally. This is usually caused by another repository
pushing to the same ref. You may want to first integrate the remote
changes (e.g., 'git pull ...') before pushing again.
See the 'Note about fast-forwards' in 'git push --help' for details.
* 3fc556d (HEAD, master) New text
* ba74a5a (origin/master) Merge branch 'michael'
|
| * bd8bf6e Micha branch
* | 57cdc9a Code addded
|/

git pull --rebase
● You have not shared the commit, so rebase for
clean history with the remote content.
● See, no non-sense merge!
* 3fc556d (HEAD, master) New text
* ba74a5a (origin/master) Merge branch 'michael'
...
Local ~mytest$ git pull --rebase origin master
...
Applying: New text
* 85f62f6 (HEAD, master) New text
* c2e9a1a (origin/master) One more thing added
* ba74a5a Merge branch 'michael'
|
| * bd8bf6e Micha branch
...

git pull – the ugly merge
● By default you get a merge when you have local
changes
* 2272ff5 (HEAD, master) No stuff anymore
* f5d6db1 (origin/master) Entry 10
* fd4fdd7 Entry 9
Local ~mytest$ git pull origin master
...
From ssh://gitlab.foobar.de/asdf/traning
* branch master -> FETCH_HEAD
f5d6db1..d39a17e master -> origin/master
asdf.txt | 0
1 file changed, 0 insertions(+), 0 deletions(-)
create mode 100644 asdf.tct
* d1247b3 (HEAD, master) Merge branch 'master' of ssh://gitlab.foobar.de...
|
| * d39a17e (origin/master) New file
* | 2272ff5 No stuff anymore
|/
* f5d6db1 Entry 10

A small shared
workflow
Just you, git, and other dudes or dudettes.

Let me flow alone
# get the master latest changes
Local ~(master)$ git pull --rebase origin master
# create a new branch with a meaningful name and switch
Local ~(master)$ git checkout -b jaropener-4210
# do some development
Local ~(jaropener-4210)$ git add File.java; git commit -m “base class”
Local ~(jaropener-4210)$ git add .; git commit -m “tests added”
# switch to master
Local ~(jaropener-4210)$ git checkout master
# get the latest master changes, no local changes assumed
# switch to branch
Local ~(master)$ git checkout jaropener-4210
# rebase branch against master, assuming you have not pushed your branch!
Local ~(jaropener-4210)$ git rebase master
# switch to master
Local ~(jaropener-4210)$ git checkout master
# merge the branch in without fast-forward to get a single commit
Local ~(master)$ git merge --no-ff jaropener-4210
# delete the branch now, you merged it!
Local ~(master)$ git branch -d jaropener-4210
# refresh your master, no further local changes
# push your work and be happy
Local ~(master)$ git push origin master

Merge vs. Rebase
The common misunderstanding

But SVN...
●
SVN does not have a rebase
●
Server counts up and each commit gets a number
●
What is merged ends in mergeinfo properties
●
Git uses a cryptographic hash to protect content
●
Includes the parents in that aka new parent, new
hash
●
It is non-linear but linear... confused?
●
Git forms a chain of content

Rebase vs. Merge
●
Rebase
●
Makes your work latest
●
Set's your work aside, updates branch, puts your work
on top of it, so your work wins mostly
●
Removes all your commits and creates them new
●
Bad when already shared
●
Merge
●
Fits your work into the timeline
●
Uses the timeline to figure out who is right
●
Creates a commit with the merge content

Local rebase and merge visualized
HEAD
aa 1245aab ccbb master
aa 1245aab ddbb mybranch
aa 1245aab ccbb master
dddd
git rebase master
aa 1245aabbb mybranch
HEAD
cc
aa 1245aabbb master
git merge --no-ff mybranch
ff
HEAD
ee
eeee
eedd
cc

Rebase from remote visualized
HEAD
a54341b 1245aab c3dffd1 19ab4dda54341b master
a54341b 1245aab c3dffd1 561abcda54341b origin/master
a54341b 1245aab c3dffd1 561abcda54341b master61b48aa
git pull --rebase origin master
a54341b 1245aab c3dffd1 561abcda54341b
origin/master
git push origin master
a54341b 1245aab c3dffd1 561abcda54341b 61b48aa
origin/master
a54341b 1245aab c3dffd1 561abcda54341b master61b48aa
HEAD
HEAD

Remote merge visualized
a54341b 1245aab c3dffd1 19ab4dda54341b master
a54341b 1245aab c3dffd1a54341b master
git pull origin master
561abcd
a54341b 1245aab c3dffd1a54341b master
git push origin master
a54341b 1245aab c3dffd1a54341b origin/master
561abcd
561abcd
981715a
19ab4dd 981715a
19ab4dd 981715a
19ab4dd
HEAD
HEAD
HEAD

When to rebase
● When you cannot push because someone was
faster: git pull --rebase
● When you have not shared anything and want to
have a clean branch and solve the possible merge
conflicts before merging
● When you do not care about your base

When rebase becomes evil
● When you shared commits already
● When you branch off of the to-be-rebased branch
aka you shared you commit with yourself already
● When you already merged in from other branches
● Do not forget, squashing means rewriting too
Rebasing means rewriting of commits!

Rebase kills merges
● A rebase after a merge removes the merge and
makes everything flat
● How ugly!
http://stackoverflow.com/questions/11863785/make-git-pull-rebase-preserve-merge-commits
Local ~mytest$ git fetch origin/master
Local ~mytest$ git rebase origin/master --preserve-merges
# Make it default to preserve (Git >= 1.8.5)
Local ~mytest$ git config pull.rebase preserve

Merge/no-ff/squash?

Misc
Does not fit anywhere else

Some other stuff
● Force branch delete: git branch -D name
● Remote delete: git push origin :name
● Stash things away: git stash save
● Get things back: git stash apply
● Remove stash: git stash drop
● Clean up after merge: git clean -f -d

Golden git advantages to use
● Always branch
● Commit often
● Not sure about a merge? New branch and try
● Rebase your branch before merge, if not shared
● Do not run anything advanced, there is barely any
reason for doing that
● Keep it simple!

Tools
In case you don't like the command line

Tools - tig

Tools - gitk

A list of tools
● GitEye
● SmartGit
● TortoiseGit
● EGit for Eclipse

git blame
Q & A
Your moment to ask questions, to show off, to blame
us for wasted life time, blame git, or blame Linus.

git resources
● Atlassian's Git Pages
● https://www.atlassian.com/git
● The official web page
● http://git-scm.com/
● Stuff about Git
● http://gitready.com/

Sources used
● http://git-scm.com/
● http://gitready.com/
● https://www.atlassian.com/git
● Subversion DB: http://commons.wikimedia.org/wiki/File:Database-vcs-subversion.svg (CC-BY-SA)
● Creative Commons icons: http://creativecommons.org/about/downloads (CC-BY)

License
● Use these slides freely
● Share them freely
● Modify them freely but share them again
Creative Commons Attribution-ShareAlike 3.0
Unported License
http://creativecommons.org/licenses/by-sa/3.0/deed.en_US

Git - The Incomplete Introduction

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