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An introduction into SCM tools, git concepts and how to use git.

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  1. 1. GIT SCM @stefanprutianu
  2. 2. SCM? Source Code Management aka! ! Version Control System! aka! ! Revision Control System
  3. 3. Why? ! collaboration ! because we need to keep track of changes: when? ! why? ! what was the content? ! who? (very important, right? :)) ! centralized SCMs: Subversion, CVS ! distributed SCMs: GIT, Mercurial
  4. 4. Centralized & Distributed checkout! commit! revert! merge! tag! branch! lock! conflict resolution.! ...
  5. 5. Centralized vs. Distributed centralized distributed master copy in one place! everyone has a full copy - distributed! single point of failure! works offline or disconnected from a server! considers data as a list of file -based changes (initial version + deltas) ! a commit operates over the central repository saves snapshots of data it manages ! a commit operates over the local repository
  6. 6. SVN model Repository Client 2 Client 1 Version 1 Version 2 File A Delta 1 Version 4 Delta 2 Delta 1 File B File C Version 3 Client n Delta 1 Time Delta 2
  7. 7. GIT model Central! Repository Client 1 ! (mirror) Client 2! (mirror) Client n! (mirror) Version 1 Version 2 Version 3 Version 4 File A File A1 File A1 File A2 File B File B File B1 File B2 File C File C1 File C1 File C1 Time
  8. 8. GIT --history British slang for "pig headed, think they are always correct, argumentative" 2005, Linux kernel maintenance (35000 files)! Linus Torvalds! written in C "So I'm sorry, but for something like git, where efficiency was a primary ! objective, the "advantages" of C++ is just a huge mistake. The fact that ! we also piss off people who cannot see that is just a big additional ! advantage." (L.T.) modern, robust, fast, distributed, great branching system, complex merges, open source! available on Mac, Windows, Linux
  9. 9. GIT --philosophy a git repository is a....graph, Directed Acyclic Graph! node = commit! edge = pointers from child nodes to parent node(s)! nodes are identified by SHA-1 hashes from: content change + parent(s) commit identifier => speed! a lot of the work done by git involves moving references (labels) around => speed
  10. 10. GIT --philosophy git references = labels assigned to commits ! several types: branch (local/remote), tag, stash! references are stored in .git/refs/heads ( the SHA-1 identifier of the commit it points to, 41 bytes)! there are references to references -> HEAD, for example, which points to the current branch! references make commits reachable
  11. 11. GIT --philosophy fast forward merge
  12. 12. GIT --philosophy
  13. 13. GIT --concepts git manages its content via 3 states: modified, staged, committed Workspace Staging ! Repository area stage commit unstage checkout Local repository
  14. 14. GIT --concepts Workspace (working directory) one version of the content, extracted from git database to be used or modified
  15. 15. GIT --concepts Staging area (index) allows you to elect files/content that is going to participate in the next commit! you can see how the next snapshot would look like before actually creating it - avoid mistakes! allows you to break changes in workspace into more than 1 single commit
  16. 16. GIT --concepts Repository where object database and metadata is stored! the .git folder inside your repository root folder
  17. 17. GIT --concepts git manages its content via 3 4 states: modified, staged, committed, stashed! ! Stash here you can save changes you want to keep but not ready to commit yet! stashes are in fact labeled nodes on the repository graph
  18. 18. GIT --concepts Stash Stash Workspace Staging ! Repository area create stage apply commit unstage checkout Local repository
  19. 19. GIT --concepts Remote repository git repository located on another machine, usually! the local repository may be a mirror of the remote one! write into it via push, read from it via pull & fetch
  20. 20. GIT --concepts Remote repository Stash Workspace Staging ! area Repository Remote repository push pull/fetch Stash Workspace Staging ! area Repository Local repository
  21. 21. GIT --concepts GIT objects blobs - contents of a file! tree - directories of blobs or other trees! commits - SHA-1 of a tree, parent commit(s), message! tags (annotated)
  22. 22. GIT --@work Create a repository git init initializes a new, empty repository, inside the current directory git clone stefanprutianu/git-scm-remote.git clones the remote repository on the local machine, inside a newly created git-scm-remote folder
  23. 23. GIT --@work Prepare a commit (stage) git add <file> | <pattern> marks the file(s) as belonging to the next commit, i.e. changes are staged git reset <file> removes the file from the staging area
  24. 24. GIT --@work Commit git commit -m "Commit message" records the commit in the repository history git commit --amend modifies the last commit by adding the staged changes
  25. 25. GIT --@work Revert git checkout -- <file> the <file> contents in working directory is replaced with the last committed one git reset --hard <branch/commit/tag> discards commits until the one pointed to by the reference git revert <commit> reverses the specified commit by creating a new one
  26. 26. GIT --@work Stash git stash saves the working directory state and pushes it on the stashes stack git stash apply gets the most recent stash and applies it to the working directory
  27. 27. GIT --@work Share changes publishing changes git push <server> <branch> pushes your changes on the specified branch of the remote repository git format-patch HEAD --stdout > mypatch.patch retrieving changes git fetch <server> pulls down all the data from the remote repo that you don't have yet on tracked branches git pull does a git pull and merges those on your current branch
  28. 28. GIT --@work Branch git branch <branch name> creates a new branch starting from your last commit git checkout -b <branch name> creates a new branch starting from your last commit and switches to it git branch -d <branch name> deletes the specified branch
  29. 29. GIT --@work Merge git merge <branch name> merges the specified branch into the current one git rebase <branch name> rebases the specified branch onto the current one
  30. 30. GIT --@work : merge master A E B C D develop using merge master A E B F D C develop using rebase master A B develop E C C' D D'
  31. 31. GIT --a branching model master develop hotfix/* feature/* tag 1.0.0 tag 1.1.0 tag 1.1.1 tag 1.5.0 http:/ /
  32. 32. GIT --@work Status git log prints out the commit tree from the current HEAD git status shows info like: current branch, working directory status, staged changes git stash show shows the most recent stash git describe shows where you are in repository history relatively to the latest tag, i.e a revision number. Eg: v1.0.0-50-g1f8115b
  33. 33. GIT --@work Status git diff <commit> shows the diff between working directory and specified commit git branch [-r] lists either local or remote (-r) branches
  34. 34. GIT --@work Status
  35. 35. GIT --@work Release management git tag v1.0.0 -m "My first release" creates a "lightweight" tag, i.e. an immovable reference on the current head git tag v1.0.0 -a -m "My first release" creates an "annotated" tag, i.e. an immovable reference on the current head + info like: tagger, email, date which are stored in the git database
  36. 36. GIT --@work Misc git cherry-pick <commit> integrates changes in specified commit into the current branch git bisect given a start and an end commit reference it will checkout commits within that range allowing to find a regression git blame annotates each line in a file with that last commit to change it
  37. 37. GIT --repository .gitignore file to express ignore patterns, can be put in multiple places! ! git repos smaller than SVN ones, 30x in case of Mozilla! ! steep learning curve (debatable)! ! can't checkout part of a repository! ! oriented towards content rather than files ! ! for transport it supports: HTTP, SSH, GIT protocols! ! objects are generally added not deleted, reason for git gc
  38. 38. GIT --how to latest release http:/ /! works from CLI! good GUI clients: Github for Mac/Win, free ("optimized" for remotes, but works with others too)! SourceTree (Mac & Win), free! Tower (Mac)
  39. 39. (Em)Powered by GIT https:/ / https:/ / https:/ /
  40. 40. GIT SCM easy branching local, flexible, fast reliable history integrity non-linear, facilitates collaboration
  41. 41. Thank you! Questions? @stefanprutianu
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