Git A fast distributed revision control system Nils Moschüring PhD Student (LMU)
1 The three W s What? Why? Workflow and nomenclature 2 Overview of gits structure Structure Branches 3 Using git Setting up Working Sharing 4 Final stuff
What is a version control system? A system which monitors data continuously Monitors means that it will detect any changes to the data and will be able to tell you about them. At every point during your work you can tell the system to take a snapshot (a record of the current status of the data). You can let others change your data and these changes will also be recorded. A friend with benefits (on top of the above) Everything is saved with a timestamp and user information (making it easy to pinpoint and blame the source of a mistake). All changes can easily be reverted to any previous state. You can even revert to a previous version, fix an error and automatically redo all the other good stuff!
Why do I need it? Single User: This functionality greatly simplifies the development process of digital products. Especially the development of software. Multi User: Everybody can change whatever he wants, without consulting anybody else. All the modifications by all the different users will be merged to one final result automatically. If they don t overlap. Different branches are supported.they enable you to work on a specific subproblem separately. Of course, these can later be merged without trouble. If they don t overlap.
Workflow - Commit
Workflow - Commit
Workflow - Checkout
Workflow - Merge
Workflow - Branches
Git is a distributed RCS
Working Copy - Index - Repository Working Directory Index Repository checkout add reset commit
Branches How do they work? different versions of the same overall functionality (overlaps) experimental stuff, tryouts parallel development on the same trunk What branches do I have and why: Run git branch -a Git keeps copies of all branches on your source repository marked with a remotes/ prefix. If you run the git fetch command, these local copies will be updated. git fetch makes changes from a different repository available in your repository. You can create new remotes with the git remote command. You can set an alias (as origin in the cloned case). The branches marked as remotes/ can not be checked out. You have to create a local branch which tracks the remote one. Tracking means, that git pull and git push will use these branches as a default.
Branches - workflow example: new features & multi users Testing V1 V2 V3 branch merge merge Master V1 V2 V3 V4 V5 commits
Branches - workflow example: different versions microwave V1 V2 V3 branch merge oven V1 V2 V3 V4 V5 branch merge grill V1 V2 V3
Using git: Setting up Configuring Git Run: git config --global user.name "Bob" git config --global user.email "bob@bob.com" Setting up a local repository git init Copying (Cloning) an existing repository git clone GIT-URL Possible GIT-URLs (only ssh and local shown): ssh://[user@]host.xz[:port]/path/to/repo.git/ [user@]host.xz:path/to/repo.git/ /path/to/repo.git/
Using git: working The git checkout command Checks out a branch: Sets your repository (called the HEAD) to the last commit of the branch, sets your index and your working directory to the desired branch data. Important Command line argument: -b Create a new branch and switch to it The git add command Puts local changes into the index on a file by file basis. The git diff command Shows the difference between your working copy and the index. The git status command Shows the current status of your working directory, index and repository.
Using git: working The git commit command Puts the changes in the index into the repository creating a new checkpoint (commit). Important Command line argument: -a Includes adding all changes to the index. The git branch command Creates a new branch or shows the existing branches. Important Command line arguments: -a Shows all existing branches -d Deletes a branch (verifying that the changes are in the current branch) -D Delete a branch without verifications Example: git branch my_testing remotes/origin/testing creates a new local branch named my testing which is tracking the branch named testing on the origin repository.
Using git: working The git merge command Normally you will use it to merge a branch you will abandon back into your main branch. To do that, checkout the main branch and do git merge soon-to-be-abandoned-branch If there are conflicts (the two branches differ in the same line), git will leave conflict markers. They look like this: <<<<<<< master Content of line x in branch master ======= Content of line x in branch local >>>>>>> local Resolve them and commit the result! The gitk command This will show a nice graphical representation of your repository, the branches and their relations. A good alternative for Mac OS X is GitX which can be found on MacPorts.
Using git: sharing The git pull command Consists of the git fetch and the git merge command as follows The first parameter can be a repository GIT URL. It is used to fetch from. The results are normally stored in the local remotes/remote-alias/ branches. The second parameter is the branch on the foreign repository to be used in the merge command. If you ve set up your tracking branches, git will automatically know all of the above and a git pull without any arguments updates your local branch to the respective branch on the remote repository. This command always modifies the currently checked out branch! Of course this could cause merge conflicts...
Using git: sharing The git push command Tries to update a branch on a remote repository. Normally works only for fast forwards, i.e. merges with no conflicts (there are good reasons) You can force a push, but if you do, it will NOT do a merge! If the push doesn t work, the normal procedure would be to do a pull first, resolve the problems and then push the new commit, which is then directly descendent from the current status on the repository. Nice feature: hooks You can make interesting things happen to a repository every time you push into it... - http://www.kernel.org/pub/software/scm/git/docs/git-push.html
Using git: advanced git commands The git rebase command Rewriting of history Squashing of commits Creating a linear history The git grep command Improved searching in repositories Follows the same basic syntax as Unix grep The git stash command Puts your changes to a safe place and resets the working directory and index Handy for quick looks into different branches without having to create a commit
Final stuff Of course there are many more really useful commands you should use, please discover them on your own. References I used: http://book.git-scm.com/index.html http://www.kernel.org/pub/software/scm/git/docs/git.html Take-Home-Message USE GIT