Version Control with CVS

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1 Version Control with CVS Robert Dondero February 4, 2011 This document was written by Robert Dondero, borrowing heavily, often word-for-word, from a document entitled "Version Control with Subversion" written by Matthew Plough.. 1 Introduction CVS, the Concurrent Versions System, is a version control system. A well-written free book on CVS entitled Open Source Development with CVS can be found at In this document, I present only a brief overview of the concept of version control and how to use CVS as administered by Princeton's Computer Science Department. 2 Version Control The COS 333 course requires you to use a version control system for your assignments and project. It does so for a number of reasons. Without one, you ll have problems sharing code; you would need to find a place that all of your group members can access when you aren t all present, and it will be frustrating for all of you to work on the code at the same time. In the past, you have probably deleted critical files inadvertently, and frantically sought to retrieve them. While trying to find a bug, you have probably added so many changes to a file that you can no longer remember what the code originally looked like, so you may have to rewrite the code completely. Version control systems address all of these problems, allowing you to write code more efficiently. Chapter 2 of the aforementioned book gives an overview of how version control works. If you have not used a version control system before, it s essential reading. 2.1 The Repository All versions of your work are stored in a central location called a repository; any of them can be retrieved at any time. With CVS, creating a repository is easy; I describe how to do so in Section 3. The repository acts as a vault for a project; it changes how you work with your code. Instead of working on the only copy of your project, you check out a copy of the project, make changes, and commit the changes back to the repository. This gives a lot of flexibility; if you make changes that prove useless, you can quickly revert back to a known-good version of your work. Similarly, if you accidentally delete a file, you restore the last version from the repository. Page 1 of 6

2 Repositories are generally quite small; only the minimum amount of information needed to construct a given version of a file is stored. If a file does not change between versions, a new copy is not written. The CS Department backs up all of its CVS repositories regularly and so you will not have to worry about losing your entire project. 2.2 The Working Copy Once you have finished setting up a repository, any member of your group can check out files from the repository; this local copy of the code is called the working copy. Each group member can make changes to his or her own working copy, and once satisfied with the changes, commit them back into the repository for others to access. 3 Getting Ready to Work Your first step should be to read Chapter 2 of the "Open Source Development with CVS" book. This section contains enough information to get you up and running on penguins. Your second step should be to browse to click on the "User's Guide" link, and read the resulting page. When getting started, it's safe to ignore the "Account Management" section of that page. These are the specific steps that you should take: 3.1 Register with cvs.cs.princeton.edu. 1. Browse to Click on the "Register" link. In the resulting page, fill in these fields: Full Address: YourPrinceton Address Confirm Address: YourPrinceton Address New Password: SomeNewPassword Verify Password: SomeNewPassword First Name: YourFirstName Last Name: YourLastName Full initials: YourInitials 2. For "User Type" chose "Local". 3. For "CS Unix Username" type YourLoginId. 4. For "Password" type YourCsPassword. 5. Click on the "Register" button Create a repository 1. Browse to Page 2 of 6

3 2. Click on the "Start a Repository" link. 3. Type YourPrinceton Address as your user name and SomeNewPassword (as defined in the previous step) as your password. 4. For the repository name type cos333followedbyyourinitials. (Thus, for example, your repository name might be "cos333abc".) 5. Chose "Collaborative", and not "Personal". Other members of your team can "join your repository" by browsing to clicking on the "Join a Repository" link, and following the instructions on the resulting page. 3.3 Create a CVSROOT environment variable In this step the goal is to create an environment variable on penguins that cvs commands will use to contact your repository. 1. Using a terminal program, log into penguins. 2. Add this command to the.bashrc file in your home directory: export CVSROOT=:ext:YourInitials-YourRepositoryName@cvs.cs.princeton.edu:/cvs For example, the command might be: export CVSROOT=:ext:abc-cos333abc@cvs.cs.princeton.edu:/cvs 3. Log out of penguins. 3.4 Create a project within your repository 1. Using a terminal program, log into penguins. 2. Issue a cd command to move to the directory containing your Assignment 1 files (or, perhaps, to a dummy directory containing a dummy file or two if you haven't yet created any of your Assignment 1 files ). 3. Issue this command: cvs import -m "initial import" Asgt1 YourLoginId start That command creates an Asgt1 project within your repository. The Asgt1 project contains all of your Assignment 1 (or dummy) files. 3.5 Create a working copy of your project Page 3 of 6

4 1. Using a terminal program, log into penguins. 2. Issue a mkdir command to create a new directory named, say, workingcopy. 3. Issue a cd command to move to workingcopy. 4. Issue this command: cvs checkout Asgt1 5. Issue a cd command to move to workingcopy/asgt1. Note that the workingcopy/asgt1 directory contains a working copy of your Asgt1 project. 4 Learning to Use CVS First and foremost, read Chapter 3 of the Open Source Development with CVS book. Then Learn the most commonly used commands To add a file to the repository: emacs NewFileName That is, create a new local file cvs add NewfileName cvs commit -m 'some message' NewFileName To remove a file from the repository: rm ExistingFileName That is, delete the local file cvs remove ExistingFileName cvs commit -m 'some message' ExistingFileName To edit a file and commit that file back to the repository: emacs ExistingFileName That is, edit the local file cvs commit -m 'some message' ExistingFileName To commit all edited files back to the repository: cvs commit -m 'some message' To fetch the most recent files from the repository: cvs update Page 4 of 6

5 4.2 Know how to handle conflicts! Be especially sure to understand how to handle a conflict. There are two ways, (1) reverting your local changes, and (2) editing the file to taste, and running cvs commit. You can create a conflict with the following procedure: 1. Have two group members check out working copies. 2. Group member A creates a file foo, edits it, and adds it to the repository. Group member A commits foo. 3. Group member B performs an update. 4. Both group members edit line 5. A changes it to read one thing; B changes it to read something else. 5. A commits. 6. B updates. B s version is now conflicted. 4.3 Use informative commit messages When committing changes, supply an informative message saying what you did and why. This is useful when other group members want to know what changed, or when you are trying to diagnose the source of a problem. If done correctly, these messages can help you write your documentation. There are three ways to specify a commit message: On the command line. In a file. When committing, run: $ cvs commit -m 'informative message' ExistingFileName This is useful when your message is something trivial like forgot to add the makefile. You can also write up your changes in a file before the commit, and specify the file containing your message while committing, like so: $ cvs commit -F FileContainingYourMessage ExistingFileName You ll want to delete the file after writing it, since its contents will be available in the commit log. With an editor, at commit-time. Page 5 of 6

6 Recommended. You can also have CVS open a temporary file in a text editor when you run the commit command. When you save the changes and exit, CVS will place the file s contents in the log, and delete the file. To do this, export the path to your favorite editor in an environment variable called EDITOR in your.bashrc file by adding the line (for example): export EDITOR='emacs -nw' Then, to commit, run: cvs commit ExistingFileName Page 6 of 6

Portions adapted from A Visual Guide to Version Control. Introduction to CVS

Portions adapted from A Visual Guide to Version Control Introduction to CVS Outline Introduction to Source Code Management & CVS CVS Terminology & Setup Basic commands Checkout, Add, Commit, Diff, Update,