getting git

Basics

• Decentralized
• Fast
• Flexible

Local VCS

(rcs)

Centralized VCS

(cvs, svn)

Yay

• Access control
• Central Backup

Nay

• Single point of failure
• Painful merges

Decentralized VCS (git)

(git, mercurial, bazaar, bitkeeper, darcs)

Yay

• Every clone is a fork

• Every clone is a backup

• No connectivity issues

• Cheap branching

• Fast. Really!

• Rewriting history is possible and easy

• Flexible workflows for development, review & deployment

Nay

• Not good for large binary files (workaround: LFS)

• File permissions are not tracked (except +x)

Git design goals

• Speed

• Simple design

• Strong support for thousands of parallel branches

• Fully distributed

• Able to handle larges projects like Linux kernel effectively

• Ensure integrity

https://youtu.be/4XpnKHJAok8

Tracking Changes

(most VCS)

Changes to files are tracked.

Tracking Snapshots

(git)

Conceptually, git tracks snapshots.

(On the storage level, deduplicated deltas are used.)

Git is a file system

Git thinks of its data more like a set of snapshots of a mini filesystem.

Git has integrity

• Everything is checksummed

• References are SHA-1

• If you check out the same commit ID,

you have the same content.

24b9da6552252987aa493b52f8696cd6d3b00373

Git doesn't delete

• Git generally only adds data

• If you mess up, you can usually recover your stuff

• Recovery can be tricky though

The three states

Modified
Staged
Committed

Workflow

The git directory

• Located at .git/

• Contains entire history

The working directory

• A single checkout from a Git repository

The Staging Area

• Contained in a file

• Tracks what will go into the next commit

• AKA "the index"

File Status Lifecycle

Configuration

Identity

$ git config --global user.name "John Doe"
$ git config --global user.email johndoe@example.com

Editor

$ git config --global core.editor vim

Colors

$ git config --global color.ui true

Creating a Repository

$ git init

Cloning a Repository

$ git clone https://github.com/dbrgn/fahrplan

Creating a Commit

Specific changes:

$ git add *.py

$ git add README.rst

$ git commit -m 'First commit'

All tracked changes:

$ git commit -am 'First commit'

Removing files

From staging area

$ git rm --cached file.py

From index and file system

$ git rm file.py

Moving files

Git tracks content, not files. Although there is a move command...

$ git mv file1 file2

...this is the same as...

$ mv file1 file2

$ git rm file1

$ git add file2

Show Status

$ git status

Show log

Entire (paged)

$ git log

Date filtering

$ git log --since=2.weeks

$ git log --since="2 years 1 day 3 minutes ago"

SHOW Diffs

Unstaged changes

$ git diff

Staged changes

$ git diff --cached

Relative to specific revision

$ git diff 1776f5

$ git diff HEAD^

$ git diff awesomebranch

Show Commits

Last commit

$ git show

Specific commit

$ git show 1776f5

$ git show HEAD^

Undoing Things

Overwrite last commit

$ git commit --amend

Unstage staged file

$ git reset HEAD file.py

Unmodify modified file

$ git checkout file.py

.gitignore

$ cat .gitignore
*.pyc
*.swp
/build/
/doc/[abc]*.txt
.pypirc
*.egg-info

• Blank lines or lines starting with # are ignored

• Standard glob patterns work

• End pattern with slash (/) to specify a directory

• Negate pattern with exclamation point (!)

• Subdirectories can have their own .gitignore files

Remotes

• Other clones of the same repository

• Can be local (another checkout) or remote (coworker, central server)

• There are default remotes for push and pull

$ git remote -v
origin git://github.com/schacon/ticgit.git (fetch)
origin git://github.com/schacon/ticgit.git (push)

Push to remote

Without default

$ git push <remote> <rbranch>

Setting A default

$ git push -u <remote> <rbranch>

Then...

$ git push

Pull from Remote

Fetch & Merge

$ git pull [<remote> <rbranch>]

Fetch & Rebase

$ git pull --rebase [<remote> <rbranch>]

-> Rebasing modifies commits!

Create Tags

Lightweight tags

$ git tag v0.1.0

Annotated tags

$ git tag -a v0.1.0 -m 'Version 0.1.0'

GPG-Signed tags

$ git tag -s v0.1.0 -m 'Signed version 0.1.0'

$ git tag -v v0.1.0

Branches

Branches are "Pointers" to commits.

Diverging Branches

Branches can diverge.

Merging Branches

Branches can be merged.

Merge conflicts

• Different auto-merge strategies

(fast-forward, 3 way, etc...)

• If it fails, fix by hand

$ git merge iss53
Auto-merging index.html
CONFLICT (content): Merge conflict in index.html
Automatic merge failed; fix conflicts and then commit the result.

• Then mark as resolved and trigger merge commit

$ git add index.html
$ git commit

Usually painless

Rebasing

• Linear alternative to merging

• Rewrites tree! Never rebase published code!

Branch Management

Create new branch

$ git branch iss53

Switch Branch

$ git checkout iss53

Create & Switch

$ git checkout -b iss53

Delete Branch

$ git branch -d iss53

Branch Management

Show local Branches

$ git branch
  iss53
* master
  testing

SHOW LOCAL + remote BRANCHES

$ git branch
  iss53
* master
  testing
  remotes/origin/master
  remotes/origin/testing
  remotes/origin/iss32
  remotes/origin/iss48

Branch Management

Merged branches

$ git branch --merged
  iss53
* master

Unmerged branches

$ git branch --no-merged
  testing

Stashing

Move changes to a separate "stash".

$ git stash

$ git stash pop

$ git stash list

$ git stash apply

$ git stash drop

$ git stash clear

Common Workflow

Workflow 1

• Only commit stable code to master

• Commit unstable to develop

• Deploy hotfixes to master

Workflow 2

• Commit development code to master

• Create tags for stable releases

• Branch from stable tag for hotfixes

Topic Branches

• AKA feature branches

• For each feature, create a topic branch

• Merge early, merge often

• If desired, squash commits

Legit

Easier workflow for Git. Looks legit.

Advanced Git

Autocompletion

$ echo "source ~/.git-completion.bash" >> ~/.bashrc

Aliases

$ git config --global alias.co checkout

$ git co HEAD

Advanced Git

Partial add

$ git add -p file.py

Bisecting

$ git bisect start

$ git bisect bad

$ git bisect good v1.0

Advanced Git

Rewrite commits

$ git filter-branch --env-filter

'if [ $GIT_AUTHOR_EMAIL = gezuru@gmail.com ]; then GIT_AUTHOR_EMAIL=db@threema.ch; fi; export GIT_AUTHOR_EMAIL'

Resources

• "Pro Git" Book http://git-scm.com/book

• Git reference http://git-scm.com/docs

• Github git challenges http://try.github.com/

• Cheat sheet http://wbrp.li/14Dqrgh

• Use git-svn-bridge http://wbrp.li/XnpaUp

• Commands git vs svn http://wbrp.li/YCw4bb