A Practical Introduction to git
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This document provides an introduction to using git for version control. It outlines three scenarios: 1) a single developer using a local repository, 2) a team of developers using a central remote repository, and 3) contributing to a software project hosted on GitHub. The document demonstrates how to initialize repositories, add and commit changes, branch, merge, resolve conflicts, push and pull from remote repositories, and set up a shared remote repository. It provides summaries of key git commands and demonstrations of workflows through examples.
![git
git
usage: git [OPTIONS] COMMAND [ARGS]
The most commonly used git commands are:
add Add file contents to the index
commit Record changes to the repository
diff Show changes between commits, commit a
...
git help <command>
git status
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![Single+Local git. Add.
git add file1 [file2 ...]
Adds new files for next commit.
Adds content from working dir to the staging area (index)
for next commit.
DOES NOT add info on file permissions other than
exec/noexec (755 / 644).
DOES not add directories per se.
working
directory
staging
area
master
git add
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![Single+Local git. Commit.
git commit [-m "Commit message."]
Records changes from the staging area to master.
working
directory
staging
area
master
git commit
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![Single+Local git. Commit names. OPTIONAL
Every commit is a git-object.
The history of a project is a graph of objects referenced by
a 40-digit git-name: SHA1(object).
SHA1(object) = 160-bit Secure Hash Algorithm.
Examples:
$ git commit README -m "Added README."
[master dbb4929] Added README.
1 files changed, 1 insertions(+), ...
or
$ git log
commit dbb49293790b84f0bdcd74fd9fa5cab0...
Author: Emanuele Olivetti <olivetti@fbk.eu>
Date: Wed Sep 15 00:08:46 2010 +0200
...
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![multi+remote/shared git. Conflicts.
How to resolve conflicts.
1 See where conflicts are:
git diff
2 Edit conflicting lines.
3 Add changes to the staging area:
git add file1 [...]
4 Commit changes:
git commit -m "Conflicts solved."
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A Practical Introduction to git
- 1. A Practical Introduction to git Emanuele Olivetti NeuroInformatics Laboratory (NILab) Bruno Kessler Foundation (FBK), Trento, Italy Center for Mind and Brain Sciences (CIMeC), University of Trento, Italy http://nilab.fbk.eu [email protected] 1 / 69
- 2. Outline Version Control: git. Scenario 1: single developer, local repository. Demo single+local Scenario 2: Team of developers, central remote repository. Minimalistic. Demo multi+remote Branching. Scenario 3: Contributing to a Software Project hosted on GitHub. Extras: how to set up centralised repository, and more. 2 / 69
- 3. Version Control: Naming & Meaning Wikipedia “Revision control, also known as version control, source control or software configuration management (SCM), is the management of changes to documents, programs, and other information stored as computer files.” Popular Acronyms: VC SCM Misnomer: Versioning Q: have you ever used VC? (raise your hand = YES) 3 / 69
- 4. Version Control: Local, Centralized, Distributed From Pro Git, S.Chacon 2009, CC 3.0 license. 4 / 69
- 5. Survey: git Q1: Have you heard about git? Q2: Do you use git? Q3: Why the “git” name? (from git FAQ) 1 Random three-letter combination that is pronounceable. 2 Acronym (global information tracker). 3 Irony. 5 / 69
- 6. git? Why “git”? Linus Torvalds: “I name all my projects after myself. First Linux, now git.” http://www.merriam-webster. com/dictionary/git 6 / 69
- 7. git git usage: git [OPTIONS] COMMAND [ARGS] The most commonly used git commands are: add Add file contents to the index commit Record changes to the repository diff Show changes between commits, commit a ... git help <command> git status 7 / 69
- 8. git Introduce yourself to git: git config --global user.name "Emanuele Olivetti" git config --global user.email "[email protected]" 8 / 69
- 9. git. Single developer + local repository. Scenario 1: single developer + local repository. 9 / 69
- 10. Single+Local git. Motivations. Q: do you use VC for local repo? Why VC for single developer + local repository? First step towards a shared project. Backup. To keep the memory of your work. 10 / 69
- 11. Single+Local git. Init. git init Creates an empty git repository. Creates the git directory: .git/ working directory staging area master Note: it is safe. It does not change your pre-existing files. 11 / 69
- 12. Single+Local git. The tracking process. git add <filename> working directory staging area master git add git commit git commit -m "Let us begin." Wikipedia “A staging area is a location where organisms, people, vehicles, equipment or material are assembled before use”. 12 / 69
- 13. Single+Local git. Add. git add file1 [file2 ...] Adds new files for next commit. Adds content from working dir to the staging area (index) for next commit. DOES NOT add info on file permissions other than exec/noexec (755 / 644). DOES not add directories per se. working directory staging area master git add 13 / 69
- 14. Single+Local git. Commit. git commit [-m "Commit message."] Records changes from the staging area to master. working directory staging area master git commit 14 / 69
- 15. Single+Local git. Commit. git commit file1 file2 Records all changes of file1, file2 from working dir and staging area to master. working directory staging area master git commit <filename> git commit -a Records all changes in working dir and staging area. Be Careful! 15 / 69
- 16. Single+Local git. Commit names. OPTIONAL Every commit is a git-object. The history of a project is a graph of objects referenced by a 40-digit git-name: SHA1(object). SHA1(object) = 160-bit Secure Hash Algorithm. Examples: $ git commit README -m "Added README." [master dbb4929] Added README. 1 files changed, 1 insertions(+), ... or $ git log commit dbb49293790b84f0bdcd74fd9fa5cab0... Author: Emanuele Olivetti <[email protected]> Date: Wed Sep 15 00:08:46 2010 +0200 ... 16 / 69
- 17. Single+Local git. Diff. git diff Shows what changes between working directory and staging area (index). working directory staging area master git diff 17 / 69
- 18. Single+Local git. Diff. OPTIONAL Q: “git add” then “git diff”. What output? git diff --cached shows differences between index and last commit (HEAD). working directory staging area master git diff --cached 18 / 69
- 19. Single+Local git. Logs. git log Shows details of the commits. git log working directory staging area master 19 / 69
- 20. Single+Local git. Logs. gitk GUI to browse the git repository. 20 / 69
- 21. Single+Local git. “How to clean this mess??” OPT. git checkout <filename> Get rid of what changed in <filename> (between working dir and staging area). working directory staging area master git checkout <file> <dir> 21 / 69
- 22. Single+Local git. Time travelling. OPTIONAL Back to the past when you did commit dbb49293790b84... git checkout dbb4929 ...and now, back to the present! git checkout master 22 / 69
- 23. Single+Local git. “How to clean this mess??”. OPT. First read carefully git status. If you panic: git reset --hard HEAD Restore all files as in the last commit. working directory staging area master git reset --hard git reset --hard Warning: reset can destroy history! 23 / 69
- 24. Single+Local git. (Re)move. OPTIONAL Warning: whenever you want to remove, move or rename a tracked file use git: git rm <filename> git mv <oldname> <newname> Remember to commit these changes! git commit -m "File (re)moved." 24 / 69
- 25. Single+Local git. Demo. Demo: demo_git_single_local.txt 25 / 69
- 26. multi+remote/shared git. Scenario 2: multiple developers + remote central repository. 26 / 69
- 27. multi+remote/shared git. shared repository developer developerdeveloper 27 / 69
- 28. multi+remote/shared git. working directory staging area master git add git commit git checkout git merge git push git fetch Local Remote master remote/ origin/ master 28 / 69
- 29. multi+remote/shared git. git clone <URL> Creates two local copies of the whole remote repository. Remote master Available transport protocols: ssh://, git://, http://, https://, file:// Ex.: git clone https://github.com/ASPP/pelita.git git remote -v shows name and URL of the remote repository. 29 / 69
- 30. multi+remote/shared git. git clone <URL> Creates two local copies of the whole remote repository. working directory staging area master Local Remote master remote/ origin/ master git clone Available transport protocols: ssh://, git://, http://, https://, file:// Ex.: git clone https://github.com/ASPP/pelita.git git remote -v shows name and URL of the remote repository. 30 / 69
- 31. multi+remote/shared git. Fetch. git fetch Downloads updates from remote master to local remote master. The local master, staging area and working directory do not change. working directory staging area master git fetch Local Remote master remote/ origin/ master Q: Why origin? A: Just a label for Remote. Choose the one you like. 31 / 69
- 32. multi+remote/shared git. Merge. git merge Joins development histories together. Warning: can generate conflicts! Note: it merges only when all changes are committed. working directory staging area master Local Remote master git merge remote/ origin/ master git fetch + git merge = git pull 32 / 69
- 33. multi+remote/shared git. Conflicts. Conflict! ... <<<<<<< yours:sample.txt Conflict resolution is hard; let’s go shopping. ======= Git makes conflict resolution easy. >>>>>>> theirs:sample.txt ... 33 / 69
- 34. multi+remote/shared git. Conflicts. How to resolve conflicts. 1 See where conflicts are: git diff 2 Edit conflicting lines. 3 Add changes to the staging area: git add file1 [...] 4 Commit changes: git commit -m "Conflicts solved." 34 / 69
- 35. multi+remote/shared git. git push Updates remote masters (both Local and Remote). Requires fetch+merge first. working directory staging area master git push Local Remote master remote/ origin/ master 35 / 69
- 36. multi+remote/shared git. Demo: demo_git_multi_remote.txt. Other related files: create_remote_repo_sn.sh collaborator1.sh collaborator2.sh collaborator2.sh 36 / 69
- 38. Branching. git commit (C0) git commit (C1) git commit (C2) working directory staging area master Local Remote master remote/ origin/ master 38 / 69
- 39. Branching. git branch iss53 git checkout iss53 git checkout master working directory staging area master Local Remote master remote/ origin/ master iss53 39 / 69
- 40. Branching. git branch iss53 git checkout iss53 git checkout master working directory staging area master Local Remote master remote/ origin/ master iss53 40 / 69
- 41. Branching. git branch iss53 git checkout iss53 git checkout master working directory staging area master Local Remote master remote/ origin/ master iss53 41 / 69
- 42. Branching. git checkout iss53 git commit (C3) working directory staging area master Local Remote master remote/ origin/ master iss53 42 / 69
- 43. Branching. git branch hotfix git checkout hotfix git commit (C4) working directory staging area master Local Remote master remote/ origin/ master iss53 hotfix 43 / 69
- 44. Branching. git branch hotfix git checkout hotfix git commit (C4) working directory staging area master Local Remote master remote/ origin/ master iss53 hotfix 44 / 69
- 45. Branching. git checkout master git merge hotfix working directory staging area master Local Remote master remote/ origin/ master iss53 hotfix 45 / 69
- 46. Branching. git checkout iss53 git commit (C5) working directory staging area master Local Remote master remote/ origin/ master iss53 46 / 69
- 47. Branching. git checkout master git merge iss53 working directory staging area master Local Remote master remote/ origin/ master iss53 hotfix 47 / 69
- 48. Contributing through GitHub Scenario 3: contributing to a software project hosted on GitHub. 48 / 69
- 49. Contributing through GitHub Q: Have you ever heard of GitHub? What is GitHub? Wikipedia: “GitHub is a web-based hosting service for software development projects that use git”. 5 millions repositories (Jan 2013). Commercial... ...but friendly to Free / Open Source software projects. 49 / 69
- 50. Contributing through GitHub Assumptions You use a software and feel ready to contribute to it. The software project is hosted on http://github.com Intuitive Idea You do not push your changes to the main repository. Instead you create a public copy (fork) of the main repository... ...and then push your changes to that. Then you ask the owners of the main repository if they like your changes and want to merge them (pull request). 50 / 69
- 51. Contributing through GitHub. Not for everyone ;-) https://github.com/torvalds/linux/pull/17 51 / 69
- 52. Contributing through GitHub: Recipe I 1 Register on http://github.com 2 Visit the GitHub page of the software project and Fork it: 3 Clone your copy of the project on your computer. git clone [email protected]:<login>/<project>.git 4 Create a branch to host your improvements. git branch <new-feature> git checkout <new-feature> 52 / 69
- 53. Contributing through GitHub: Recipe II 5 Add your improvements. git add <new-file> git commit -m ... 6 Push your improvements. git push origin <new-feature> 7 Send a pull request. 53 / 69
- 54. Contributing through GitHub Detailed Explanation 54 / 69
- 55. Contributing through GitHub: Detailed Explanation Remote / Upstream master There is a software project hosted on remote GitHub repository (upstream). You want to improve it. 55 / 69
- 56. Contributing through GitHub: Detailed Explanation Remote / Origin master Remote / Upstream master So you fork it by creating a (remote) copy of it: git clone --bare <UPSTREAM_URL> 56 / 69
- 57. Contributing through GitHub: Detailed Explanation working directory staging area Local Remote / Origin master remote/ origin/ master Remote / Upstream master master Now you clone your copy on your local computer: git clone <ORIGIN_URL> 57 / 69
- 58. Contributing through GitHub: Detailed Explanation working directory staging area Local Remote / Origin master remote/ origin/ master Remote / Upstream master remote/ upstream/ master master git remote add upstream <UPSTREAM_URL> git fetch upstream 58 / 69
- 59. Contributing through GitHub: Detailed Explanation working directory staging area Local Remote / Origin master remote/ origin/ master new-feature Remote / Upstream master remote/ upstream/ master master git branch new-feature upstream/master git checkout new-feature 59 / 69
- 60. Contributing through GitHub: Detailed Explanation working directory staging area Local Remote / Origin master remote/ origin/ master new-feature Remote / Upstream master remote/ upstream/ master master git add ... git commit ... 60 / 69
- 61. Contributing through GitHub: Detailed Explanation working directory staging area Local Remote / Origin master remote/ origin/ new-feature master new-feature remote/ origin/ Remote / Upstream master new-feature remote/ upstream/ master master publish your new feature: git push origin new-feature 61 / 69
- 62. Contributing through GitHub: Detailed Explanation working directory staging area Local Remote / Origin master remote/ origin/ new-feature master new-feature remote/ origin/ Remote / Upstream master new-feature remote/ upstream/ master master Notify the owners of the main repository about new-feature they: git fetch + (eventually) git merge 62 / 69
- 63. Setting up a remote+shared repository. OPTIONAL GOAL: I want to share my local repository so others can push. “Why can’t I just extend permissions in my local repo?” Yes you can... ...but your colleagues will not push (read-only). To have it read-write: set up a remote shared repository. shared repository developer developerdeveloper 63 / 69
- 64. Setting up a remote+shared repository. OPTIONAL You have a local repository and want to share it (ssh) from a remote server on which your colleagues already have access. On remote server create bare+shared repository: mkdir newproject set up proper group permissions: chmod g+rws newproject cd newproject git --bare init --shared=group On local machine push your repository to remote: git remote add origin ssh://remote.com/path/newproject git push -u origin master 64 / 69
- 65. Setting up a remote+shared repository. OPTIONAL Demo: demo_git_setup_remote.txt. 65 / 69
- 66. Credits Rike-Benjamin Schuppner Zbigniew J˛edrzejewski-Szmek Tiziano Zito Bastian Venthur http://progit.com apcmag.com lwn.net http://www.markus-gattol.name/ws/scm.html http://matthew-brett.github.io/pydagogue/ gitwash/git_development.html 66 / 69
- 67. I want to know more about git! Understanding how git works: git foundations, by Matthew Brett: http://matthew-brett.github.com/pydagogue/ foundation.html The git parable, by Tom Preston-Werner: http://tom.preston-werner.com/2009/05/19/ the-git-parable.html Excellent guides: “Pro Git” book: http://git-scm.com/book (FREE) git magic: http://www-cs-students.stanford. edu/~blynn/gitmagic/ Contributing to a project hosted on GitHub: “Gitwash”, by Matthew Brett: http://matthew-brett.github.io/pydagogue/ gitwash/git_development.html 67 / 69
- 69. License Copyright Emanuele Olivetti, 2014 This presentation is distributed under the license Creative Commons Attribution 3.0 https://creativecommons.org/licenses/by/3.0/ The diagrams of the branching example are taken from Pro Git, (copyright S.Chacon, 2009) and are distributed under the license Creative Commons 3.0 Attribution-Non Commercial-Share Alike. 69 / 69