TweetFollow Us on Twitter

Oct 00 Online

Volume Number: 16 (2000)
Issue Number: 10
Column Tag: MacTech Online

CVS: Version Control is Your Friend

by Jeff Clites <online@mactech.com>

CVS, the Concurrent Versions System, is the standard in version control systems in the Unix world. Traditional Mac users may not have used CVS before, and in fact may not have used any version control system, but it can save you numerous headaches during your development projects, and with the arrival of Mac OS X there is no longer any excuse-CVS is free and may even come preinstalled with your developer tools.

So what is a version control system? In short, it allows you to manage and track changes to the files of a project. From an operational standpoint, most systems (including CVS) are based on a central repository which contains all of the files of your project, and individual developers "check out" copies of these files, make changes to their local copies, and then "check in" their changes to the central repository. In the process, the system does three basic things for you: it helps coordinate a team of developers working on the same project (so that programmers don't interfere with other programmers working on the same files); it tracks what changes were made to what file, when they were made, why they were made, and who made them (this helps you identify the cause of a newly introduced bug and helps enforce developer accountability); and it allows you to revert to a version of your project that existed at some previous point in time (this allows you to test compatibility with previous versions or to undo destabilizing changes). Version control isn't a magic bullet or a substitute for communication between developers, but it does go a long way toward preventing common (and annoying) problems. Version control is a must when multiple developers are involved in a project, but even a single developer working alone will benefit.

The main advantage that CVS has over most if its competitors is that it uses optimistic locking rather than pessimistic locking for checked-out file. With pessimistic locking, only one developer can check out and modify a given file at one time, in order to prevent two users from stepping on each others changes in the same file. This sounds like a good idea on the surface, but in practice it can become a major impediment if users keep files checked out for long periods of time, as they would naturally do when editing them, or as they may accidentally do if they forget to check them backing in before leaving for lunch, for the day, or for vacation. Ultimately, users will resort to circumventing the system to obtain a copy of a "locked" file so that they can get some work done, and they'll have to manually reconcile their changes with the user who originally checked out the file. CVS takes a completely different approach-it doesn't lock access to files at all. Multiple users are free to check out and work on the same files at the same time, and the system takes care of merging changes together as users commit their modifications back into the central repository. The majority of the time, users don't actually end up editing the same files at the same time (even though they may have checked them out, for instance to look them over for needed changes), and even when they do CVS is able to merge these changes together automatically. In the rare case in which two users have both modified the same line of code between check-ins, CVS notifies the user of a conflict so that he can resolve it manually. This sound like it could cause a mess, but in practice it usually does just what you would have wanted, and it only makes you spend your time resolving the rare conflict when it actually does occur, rather than causing ongoing interruptions in order to ward off potential problems that never actually arise.

CVS has many strong points in addition to the above-mentioned "non-locking" behavior. For instance, it is open source and licensed under the GPL, and therefore is available free of charge. Also, despite its Unix heritage, there are GUI-based clients available for the classic Mac OS and for Windows. On the other hand, CVS is far from perfect-it has been said that it's terrible but it's the best thing around. Many if its flaws are merely nits, but they can add up to a noticeable inconvenience. To begin with, CVS shares a problem which is unfortunately common among open-source projects, namely that it has a significant amount of documentation yet it is often difficult to find the exact information you are looking for. For example, a very nice feature of CVS is that it can be configure to run over SSH, so that passwords and data are encrypted during transmission. It's hard to find a complete discussion of this feature, and the setup is such that it's easy to think that you've enabled this feature when in fact you haven't. (There also doesn't appear to be a way to force the use of SSH from the server side, i.e. to ensure that clients cannot connect insecurely.)

A second annoyance is the somewhat inconvenient handling of directories. CVS fundamentally works on a per-directory basis, and in each directory it places a "CVS" subdirectory with configuration information. This can cause problems if you duplicate a directory and forget to remove the duplicate CVS information. Under Mac OS X there are many types of "files" which are actually directories, and tools which manipulate these need to be CVS-aware so that they don't remove the CVS information when saving. Some of these "magic directories" (for instance InterfaceBuilder's .nib files) are best thought of as opaque binary files, whose contents should not be manipulated by merge tools, and there is a "wrappers" facility which allows you to treat them as such but, inexplicably, this feature is not compatible with client-server operation. Fortunately, Codefab maintains a modified version of CVS which does support both of these features, although it's a shame that the CVS maintainers don't seem to be interested in merging this back into the core distribution. This still doesn't solve the problem for "magic directories" which you don't want to treat as binary (such as EOModeler's .eomodeld files), but fortunately the latest incarnations of Apple's developer tools seem to handle the CVS directories correctly. For older version, the Omni Group has plug-ins which fix this problem, for both EOModeler and InterfaceBuilder. The directory-centric nature of CVS also has the unpleasant side-effect that you can't really remove a directory from you project - you can only remove the files which it contains. There is a workaround in that there is a setting which tells CVS not to create empty directories during a checkout, but this has the side effect that you can't place an empty directory under version control. (It's rare that you would need to, but it's important to keep in mind in case you ever do.) On a related note, you can place binary files (such as images) under version control, but you have to go through a bit of special configuration to flag them as binary so that CVS doesn't corrupt them, for instance by doing line-ending conversion. Often, these types of files do not really need to be under version-control per se, but it's very convenient to place them in your repository nonetheless so that you can maintain a complete copy of your project, especially in web development projects which tend to contain a large number of image files.

Documentation

Apple itself uses CVS for some of its internal development projects, and in fact Mac OS X Server shipped with it pre-installed. In particular it is used with the Darwin project, and there is a page on their Public Source site which serves as a good jumping-off point to find documentation and other information about CVS. Here you'll find a brief introduction to CVS concepts, by Apple's Wilfredo Sánchez. A good next stop is Jim Blandy's "Introduction to CVS", which goes into a bit more detail. Next up is "Open Source Development with CVS", a book by Karl Fogel. Generously, although this is a commercial book, the chapters on CVS itself are available for free in a variety of electronic formats. It is extensive, well-written, and a pleasant read. Finally, there is the core CVS manual, "Version Management with CVS", colloquially referred to as "the Cederqvist", for the name of its original author. It is large and complete, but it may not be the best place to start out. Finally, for an account of using CVS specifically with web development projects, take a look at "CVS Version Control for Web Site Projects".

Much of the core documentation is located on the main CVS site, CVShome.org, and it's a good place to look for additional information and to download CVS itself, despite the somewhat inconvenient organization of the site. Their documentation page has links to the most important references, including overviews of CVS and of version control, and a CVS commands quick reference. (O'Reilly has also just published their CVS Pocket Reference, if you'd like something a little more extensive and in printed form.) Also check out the CVS Bubbles site, and especially its documentation page, which has links to a number of tutorials and to other CVS sites.

Alternatives

If you're a classic Mac OS user, you'll have to run the CVS server on a Unix machine, but there are several different clients that you can run: MacCVS Pro, MacCvs, and MacCVSClient. Despite their similar names, these are separate applications. The first of these, MacCVS Pro, is sponsored by the Mozilla project, and appears to be the most current version.

Under Mac OS X, CVS should work "out of the box" thanks to the BSD layer. If you don't like the command-line version (which really is quite easy to use), there is a GUI front end, CVL (Concurrent Versions Librarian) by Sen:te. CVL works on top of the standard CVS rather than replacing it. This is nice, because it should be forward-compatible, and it also means that you can resort to the command-line version if there is some additional feature you need to use which CVL doesn't support, and you can do this without worrying that you might "mess up" any of the locally-stored administrative information.

Finally, if CVS isn't to your liking after you've tried it out, there are several alternatives, and you might want to use one of the commercial systems. For the classic Mac OS there is VOODOO (Versions of Outdated Documents Organized Orthogonally). If you need support for multiple platforms, take a look at Perforce, which seems to be well liked and is available for a wide range of operating systems, although there don't appear to be any GUI-based clients for it. (While visiting Perforce's site you might also want to check out JAM, which is a build system designed as an alternative to make, and which is used as the build system under Mac OS X's ProjectBuilder.)

 
AAPL
$111.78
Apple Inc.
-0.87
MSFT
$47.66
Microsoft Corpora
+0.14
GOOG
$516.35
Google Inc.
+5.25

MacTech Search:
Community Search:

Software Updates via MacUpdate

NeoOffice 2014.6 - Mac-tailored, OpenOff...
NeoOffice is a complete office suite for OS X. With NeoOffice, users can view, edit, and save OpenOffice documents, PDF files, and most Microsoft Word, Excel, and PowerPoint documents. NeoOffice 3.x... Read more
LibreOffice 4.3.5.2 - Free Open Source o...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
CleanApp 5.0.0 Beta 5 - Application dein...
CleanApp is an application deinstaller and archiver.... Your hard drive gets fuller day by day, but do you know why? CleanApp 5 provides you with insights how to reclaim disk space. There are... Read more
Monolingual 1.6.2 - Remove unwanted OS X...
Monolingual is a program for removing unnecesary language resources from OS X, in order to reclaim several hundred megabytes of disk space. It requires a 64-bit capable Intel-based Mac and at least... Read more
NetShade 6.1 - Browse privately using an...
NetShade is an Internet security tool that conceals your IP address on the web. NetShade routes your Web connection through either a public anonymous proxy server, or one of NetShade's own dedicated... Read more
calibre 2.13 - Complete e-library manage...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital librarian... Read more
Mellel 3.3.7 - Powerful word processor w...
Mellel is the leading word processor for OS X and has been widely considered the industry standard since its inception. Mellel focuses on writers and scholars for technical writing and multilingual... Read more
ScreenFlow 5.0.1 - Create screen recordi...
Save 10% with the exclusive MacUpdate coupon code: AFMacUpdate10 Buy now! ScreenFlow is powerful, easy-to-use screencasting software for the Mac. With ScreenFlow you can record the contents of your... Read more
Simon 4.0 - Monitor changes and crashes...
Simon monitors websites and alerts you of crashes and changes. Select pages to monitor, choose your alert options, and customize your settings. Simon does the rest. Keep a watchful eye on your... Read more
BBEdit 11.0.2 - Powerful text and HTML e...
BBEdit is the leading professional HTML and text editor for the Mac. Specifically crafted in response to the needs of Web authors and software developers, this award-winning product provides a... Read more

Latest Forum Discussions

See All

Make your own Tribez Figures (and More)...
Make your own Tribez Figures (and More) with Toyze Posted by Jessica Fisher on December 19th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
So Many Holiday iOS Sales Oh My Goodness...
The holiday season is in full-swing, which means a whole lot of iOS apps and games are going on sale. A bunch already have, in fact. Naturally this means we’re putting together a hand-picked list of the best discounts and sales we can find in order... | Read more »
It’s Bird vs. Bird in the New PvP Mode f...
It’s Bird vs. Bird in the New PvP Mode for Angry Birds Epic Posted by Jessica Fisher on December 19th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Telltale Games and Mojang Announce Minec...
Telltale Games and Mojang Announce Minecraft: Story Mode – A Telltale Games Series Posted by Jessica Fisher on December 19th, 2014 [ permalink ] | Read more »
WarChest and Splash Damage Annouce Their...
WarChest and Splash Damage Annouce Their New Game: Tempo Posted by Jessica Fisher on December 19th, 2014 [ permalink ] WarChest Ltd and Splash Damage Ltd are teaming up again to work | Read more »
BulkyPix Celebrates its 6th Anniversary...
BulkyPix Celebrates its 6th Anniversary with a Bunch of Free Games Posted by Jessica Fisher on December 19th, 2014 [ permalink ] BulkyPix has | Read more »
Indulge in Japanese cuisine in Cooking F...
Indulge in Japanese cuisine in Cooking Fever’s new sushi-themed update Posted by Simon Reed on December 19th, 2014 [ permalink ] Lithuanian developer Nordcurrent has yet again updated its restaurant simulat | Read more »
Badland Daydream Level Pack Arrives to C...
Badland Daydream Level Pack Arrives to Celebrate 20 Million Downloads Posted by Ellis Spice on December 19th, 2014 [ permalink ] | Read more »
Far Cry 4, Assassin’s Creed Unity, Desti...
Far Cry 4, Assassin’s Creed Unity, Destiny, and Beyond – AppSpy Takes a Look at AAA Companion Apps Posted by Rob Rich on December 19th, 2014 [ permalink ] These day | Read more »
A Bunch of Halfbrick Games Are Going Fre...
A Bunch of Halfbrick Games Are Going Free for the Holidays Posted by Ellis Spice on December 19th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »

Price Scanner via MacPrices.net

13-inch 2.6GHz Retina MacBook Pro on sale for...
Best Buy has lowered their price on the 2014 13″ 2.6GHz/128GB Retina MacBook Pro to $1149.99 on their online store for a limited time. That’s $150 off MSRP and the lowest price available for this... Read more
Kodak Returns to CES With New Consumer Produ...
Former photography colossus Kodak is returning to CES for the first time in three years where the Kodak booth (#21818 South Hall 1) will showcase a wide range of innovative, imaging-related products... Read more
Invaluable Launches New Eponymously -Named A...
Invaluable, the world’s largest online live auction marketplace, hhas announced the official launch of the Invaluable app for iPad, now available for download in the iTunes App Store. Invaluable... Read more
IDC Reveals Worldwide Mobile Enterprise Appli...
International Data Corporation (IDC) last week hosted the IDC FutureScape: Worldwide Mobile Enterprise Applications and Solutions 2015 Predictions Web conference. The session provided organizations... Read more
Hello Vino Wine App Launches “Safe Ride Home”...
Hello Vino has announced addition of a new “Get a Safe Ride Home” feature in its Food & Drink app with a direct connection to Uber, the technology platform that connects users with rides. The... Read more
DEVON-technologies Releases DEVONthink To Go...
Coeur d’Alene, Idaho based DEVON-technologies, LLC has updated DEVONthink To Go, its mobile companion to DEVONthink, to version 1.5. The update includes an iOS 8 extension, compatibility with the... Read more
The Apple Store offering free next-day shippi...
The Apple Store is now offering free next-day shipping on all in stock items if ordered before 12/23/14 at 10:00am PT. Local store pickup is also available within an hour of ordering for any in stock... Read more
It’s 1992 Again At Sony Pictures, Except For...
Techcrunch’s John Biggs interviewed a Sony Pictures Entertainment (SPE) employee, who quite understandably wished to remain anonymous, regarding post-hack conditions in SPE’s L.A office, explaining “... Read more
OtterBox Defender Series Case For iPad mini 3...
With their innovative Touch ID technology and ultrathin profile, the latest tranche of Apple iPads are more desirable than ever, and OtterBox has just announced the Defender Series custom-engineered... Read more
Holiday sales this weekend: MacBook Pros for...
 B&H Photo has new MacBook Pros on sale for up to $300 off MSRP as part of their Holiday pricing. Shipping is free, and B&H charges NY sales tax only: - 15″ 2.2GHz Retina MacBook Pro: $1699... Read more

Jobs Board

*Apple* Store Leader Program (US) - Apple, I...
…Summary Learn and grow as you explore the art of leadership at the Apple Store. You'll master our retail business inside and out through training, hands-on experience, Read more
Project Manager, *Apple* Financial Services...
**Job Summary** Apple Financial Services (AFS) offers consumers, businesses and educational institutions ways to finance Apple purchases. We work with national and Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.