Introduction to Git
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Git is a version control system that was created by Linus Torvalds in 2005 to facilitate distributed development of Linux. The document outlines the contents of 4 sessions on Git that cover topics such as why version control is useful, distributed version control systems, installing and configuring Git, basic and advanced Git commands, collaboration workflows, and migrating from other version control systems to Git. Hands-on exercises are included to reinforce key concepts.
![17
Hands on
Typical projects start by cloning a public repo or getting zip of source
git clone git://github.com/akmathur/demo_app2
Make a small change
Try common commands:
git status
git diff
git add .
git commit -m “[bugfix] handled zero input”
git log, git log -p, git log --since=2016/01/15
git show HEAD^
git show HEAD~2](https://image.slidesharecdn.com/introduction-to-git-141211111515-conversion-gate02/85/Introduction-to-Git-17-320.jpg)
![39
Workflow
● [Admin] merge all incoming branches into a
release branch, test
● [Admin] Merge into master and deploy to
production
● Forking workflow – open source projects
● http://git-scm.com/docs/gitworkflows](https://image.slidesharecdn.com/introduction-to-git-141211111515-conversion-gate02/85/Introduction-to-Git-39-320.jpg)
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Introduction to Git
- 2. Introductions ● Job description & Experience with Git ● Laptop, notebook & pen ● List your topics under “Make sure you cover”
- 3. Introductions ● What's your target project? Job description? ● Experience level with any VCS ● Linux or Windows? ● Laptop, notebook & pen ● List your topics under “Make sure you cover”
- 4. 4 Contents – session 1 ● Why version control ● DVCS ● History, characteristics ● Installation and config ● Hands on
- 5. 5 Contents – session 2 ● Important Concepts ● Collaborate with Git ● Rewrite history ● Development help from Git
- 6. 6 Contents – session 3 ● Debug with Git ● Working with remotes ● Advantages of Git – review ● Advanced commands
- 7. 7 Contents – session 4 ● Best practices ● Workflows ● UI ● Migrating from SVN or Clearcase to Git ● Git Internals
- 8. 8 Session 1
- 9. 9 Why version control ● History of code changes – your own & by others ● Collaborate: merge multiple changes in same file ● Revert ● Blame
- 10. 10 DVCS ● No central repo ● Ops are fast – no server ● No network required - work offline. Whole copy of the repo available locally ● Alternatives DVCS – Mercurial, BitKeeper
- 11. 11 Git's history ● Designed by Linus Torvalds in 2005 ● For speedy and distributed dev of Linux ● Git means “stupid person” ● Most widely used VCS currently ● Linux, POSIX, OS X, Windows
- 12. 12 Characteristics ● Global commit IDs – SHA1 sig, non-sequential ● Tracks patches ● Lightweight branching ● Fast
- 13. 13 Characteristics ● Good for – Large projects, large number of devs – Multiple releases – Multiple workflows ● Bad interface over an excellent technology – Non-intuitive command options – Not very good GUI
- 14. 14 Install Git Linux apt-get install git-core yum install git Windows http://www.siteground.com/tutorials/git/win_installation.htm http://msysgit.github.io http://git-scm.org git help <command> Generate Public/Private Keys
- 15. 15 Set up a repo ● New local project – git init ● On server: git init –bare – Omits working copy – .git added to folder by convention ● Get from server – git clone ● Cloud Hosted (github)
- 16. 16 Setup $ git config $ git config --global user.name "Your Name" $ git config --global user.email [email protected] Edit ~/.gitconfig to add shortcuts & colours
- 17. 17 Hands on Typical projects start by cloning a public repo or getting zip of source git clone git://github.com/akmathur/demo_app2 Make a small change Try common commands: git status git diff git add . git commit -m “[bugfix] handled zero input” git log, git log -p, git log --since=2016/01/15 git show HEAD^ git show HEAD~2
- 18. 18 Session 2
- 19. 19 Important concepts Staging area - Build commits incrementally git add git diff –-cached git reset HEAD <file name> git add git rm
- 20. 20 Important concepts Branching - easy to create, merge, destroy git branch <name> git branch git checkout <name> git branch -D <name> git merge <name> git log HEAD..<name>
- 21. 21 Collaborate ● Branching – Work on same branch or share branch names – git push -u origin <branch-name> ● Share patches – git diff, git apply
- 22. 22 Modify history git rebase -i <base commit> • Reorder commits, create linear history git revert • Undo by reversing a commit git reset • Undo by going back in history git commit –amend git checkout <filename> git reset HEAD <filename>
- 23. 23 Development help Interactive add git add -i, git add -p Tagging git tag Ask git to ignore files .gitignore Stash git stash save “bug 2 in progress” git stash pop
- 24. 24 Session 3
- 25. 25 Git basics review VCS vs DVCS Install and Setup Making a commit – staging area Common commands - log, diff, adding and removing files Branching, merging Modifying history – revert, reset, commit --amend, rebase Development help – stash, tag, add -p
- 26. 26 Debug with Git Narrow down to last working version git bisect Who put in this line git blame
- 27. 27 Rebase & Cherry-pick Move commits from a local branch into master git rebase <branch-name> Move only selected commits git cherry-pick <branch-name>
- 28. 28 Working with remote repo git remote add origin <url> git remote, git remote show <name>, git remote remove <name> git fetch git pull origin <branch-name> git push -u origin <local-branch-name> ● Pull/Push can be done to any repo. Central is by convention only ● Remote branch names are origin/<branch-name>
- 29. 29 Set up a remote repo cd /somewhere/on/hard/drive mkdir my_project.git cd my_project.git git init --bare cd /home/work/my_project git init # create some files # add all files e.g. *.cpp *.h git add * git commit -m "initial commit" git remote add origin /somewhere/on/hard/drive/my_project.git git push -u origin master
- 30. 30 Collaboration ● Configure your remotes (default “origin” should always be there) ● Commit to local repo ● git pull (or git fetch and then merge) ● Resolve merge conflicts if any ● git push
- 31. 31 Hands-on Exercises ● Someone removed a file. What did the file have when it was removed? ● Find how a file looked 2 commits ago? ● Two bug fixes were committed together in one commit. Separate them out in two different branches.
- 32. 32 Hands-on Exercises ● Get a branch from your friend's repo but push it to the central repo as your branch ● Someone committed some changes but deleted some files by mistake in that commit. How will restore the deleted files while keeping rest of the changes?
- 33. 33 Review Debug commands – git blame, git bisect Rebase & Cherry pick Remote repo – setup, pull, resolve merge conflicts, push
- 34. 34 Session 4
- 35. 35 Advantages of Git ● Lightweight branching ● Modify History ● Collaboration ● Debugging ● Distributed development
- 36. 36 Advanced commands ● git gc ● git prune ● git fsck ● git archive ● Hooks
- 37. 37 Best practices ● Commit often, 1 line commit message ● Don't rebase after push ● Use branches liberally ● Don't fear mistakes – anything can be undone
- 38. 38 Workflows Use cases: Enterprise, Central managed repo ● Get a bug or a feature ● Start a local branch ● Commit often, test, satisfy yourself ● Rebase and arrange commits ● Merge ● Ask a friend/tester to pull and test ● Push to central repo, submit for merging ● If urgent work comes, stash or switch to another branch
- 39. 39 Workflow ● [Admin] merge all incoming branches into a release branch, test ● [Admin] Merge into master and deploy to production ● Forking workflow – open source projects ● http://git-scm.com/docs/gitworkflows
- 40. 40 UI & other tools ● Gitk – graphical UI for tree view of commits ● github.com – cloud server ● Gitosis – manage permissions ● Gitolite – manage authorizations at branch & tag levels
- 41. 41 Migrate from SVN/ClearCase ● Migrate a repo to Git – Admin create git repo for deployment – Devs continue to push to SVN – Admin commits to local git and pushes it – Make SVN read-only at migration cut-off ● Labels → Tags, Branch, History & commit messages ● Commercial tools
- 42. 42 Git internals ● Tracks patches not files ● Stored in BLOBS (binary large objects) ● Folders represented as trees ● Each tree has other trees or BLOBs – along with meta data ● BLOBs expanded into files ● Immutable append only object database ● .git folder – refs, HEAD, ORIG_HEAD, obejcts
- 43. 43 Git internals ● Any amount of data goes in → a fixed sized hash comes out ● If inputs match, checksums match. If checksums match, inputs match ● Very difficult to produce two inputs with the same output. Very difficult to produce a desired target checksum ● Commit IDs are hashes of commit patches
- 44. 44 Git internals: Hash ● Git uses hashes for names ● Whenever Git saves a file – It calculates the file's hash – It stores the file under that hash – The hash becomes the file's name ● Git never says “give me file stat.h”. Instead it says “give me file 5b5beb89ba449a9271b3c34d44b529d2a2633235” ● Why? stat.h is ambiguous. Hash is never ambiguous. Also, this completely defeats corruption and tampering
- 45. 45 Git internals: Hash ● A bunch of data stored under its hash is called an object ● When the data is the contents of a file, the object is a blob ● To store a directory, Git writes out an object describing the directory's contents. Its called a tree 100644 blob 3a6f56f8a15f5f96411c267a7428fcfeff6f9bcd foo 040000 tree e79566ab21a03dfac3fb4b479b24e3d9ff379d29 doc 100644 blob 22aa6ff4684a3080367c7bb5ec366fb3bd0364c6 bar ● A commit records the state of the entire repository at a particular moment ● Commits are tamper-proof
- 47. 47 You are welcome to reach out to me at [email protected] Thanks!