Version Control. Version Control

Transcription

1 Version Control Prepared for CS Software Design by John Bell Based on slides prepared by Jason Leigh for CS 340 University of Illinois at Chicago Version Control Incredibly important when working in teams, or whenever multiple versions of a project need to be retained, recovered, and generally managed. Many tools for this: Revision Control System (RCS), Subversion (SVN), CVS, GIT etc. Ref: sion_control_software Pro Git online book: Version Control with Git, Loeliger & McCullough, O Reilly, 2 nd Edition,

2 How Previous Version Control Systems Worked E.g. SVN, Perforce, CVS Create a central repository for holding code. Upload initial codes to repository. Checkout codes to either read or modify. Edit codes. Commit edits to the repository. ( Check in ) Multiple users can checkout codes for reading, but only one at a time can checkout for editing. How Git Works Git is a distributed system. When you work on code as part of a group, you CLONE a remote repository. Git can also be used as a local repository system, for a single developer to archive multiple versions of a project. When you commit your changes you do not need to be networked to the repository server. You can push your updates later. I.e. you work with your local repository. Git has the notion of staging areas that are used to mark files that will get committed. This is really just the list of files that are monitored by git as part of a project. If you modify a file but do not stage it, it will not get committed. I.e. not all files in working directory are in git Git makes it very easy to create and switch code branches so you experiment with code ideas without damaging the main branch. 2

3 Create / edit files git add ( control list ). git init create local project OR git clone create local copy Remote repository git commit git fetch get remote updates git push copy back to origin Setup Git on Your Computer Go to: Download and install GIT for your platform. ( Right-click on directory and select git bash ) In Terminal Window: git config --global user.name John Bell git config --global user. jbell@uic.edu ( These instructions are for using git via the command line. There are also interactive versions available. ) 3

4 Creating the Initial Git Repository git init will create a new empty repository. --bare will make one without a working directory. github.com offers free repositories for students. MUST BE PRIVATE FOR USE IN THIS COURSE. One student does this, and then lists rest of group as collaborators with access. Then each member uses git clone to make a local working copy: git clone Add A New File Create/change the file(s) to update, e.g. overloading.cpp Let Git know: git add overloading.cpp This adds the file to a list of files being watched by git, but does not update the repository. The files are said to be staged. Commit the file(s): git commit git will ask you for a comment. Use vi style editing commands Or use git commit -m message to use message as the comment. This updates the LOCAL repository with a new version. ( Only the staged files are updated / created in the repository. ) Optional: If working with a cloned repository, update remote: git push origin master Origin refers to the remote repository Master refers to the master branch on the remote repository. 4

5 ( Local ) Branching It is often better to create a separate branch for development work, ( particularly with group work. ) The master branch should be kept functional. Side branches are often works in progress, not ready yet. git branch mynewbranch defines a new branch git checkout mynewbranch switch to the branch git checkout -b mynewbranch Combines steps From now on all changes occur in the new branch. To switch back to the master branch: ( Save changes to current branch before switching. ) git checkout master Updates working directory and sets the current working branch to master. ( Local ) Merging The git merge source command merges changes from the source into the current branch. To merge changes from somebranch to master: git checkout master git merge somebranch To merge changes from master to somebranch: git checkout somebranch git merge master 5

6 Merging With Remote Changes When multiple people have cloned a repository, made edits and now want to push their edits, git push will fail. Need to merge the two branches: git checkout master Sets local branch to master. [ Merge local branches to master if necessary. ] git fetch gets changes from the remote repository, only into the local repository. git merge origin/master Merges changes from the master branch on the origin into the current local working branch ( local master ). git push origin master Upload merged version How to Specify Particular Commits git checkout somebranch Switch to HEAD on named branch, often master for main branch. Commits may be specified by their unique ID, or a shorter part of it. git tag applies a more easily used name to a particular commit. Given a commit C, C~n refers to the commit n versions back. e.g. git checkout master~2, HEAD~2, or just ~2 6

7 More Useful git Commands git help git help topic git status git log git rm git mv git diff git show git branch git show-branch gitk Git In Depth Pro Git online book: Version Control with Git, 2 nd Edition: 7

8 Git Cheat Sheet git config set up git init do this if you plan to create your own local repository git clone from repository do this to bring in a remote repository git add files add files to staging area to mark for commit git commit commit the file git push origin master push the committed files to remote origin s master branch git log - show log of changes made to repository. git status - show current status of tracked files, e.g. uncommitted changes. Second person does git clone as well makes his changes tries to do push but fails must do a git fetch fetches latest updates from repository git merge merges the versions git pull does git fetch followed by git merge. git push origin master pushes it back to the server Advice for using git git is best suited for projects in which different developers are working on different ( groups of ) files. It also works well for a single developer to keep track of multiple versions of his/her work, with either a local or remote repository. It is not as well suited for multiple authors collaborating on a single document. git has some support for this, but it is complicated. 8