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.)

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

FileZilla 3.24.0 - Fast and reliable FTP...
FileZilla (ported from Windows) is a fast and reliable FTP client and server with lots of useful features and an intuitive interface. Version 3.24.0: New The context menu for remote file search... Read more
Bookends 12.7.8 - Reference management a...
Bookends is a full-featured bibliography/reference and information-management system for students and professionals. Bookends uses the cloud to sync reference libraries on all the Macs you use.... Read more
Duplicate Annihilator 5.8.3 - Find and d...
Duplicate Annihilator takes on the time-consuming task of comparing the images in your iPhoto library using effective algorithms to make sure that no duplicate escapes. Duplicate Annihilator detects... Read more
BusyContacts 1.1.6 - Fast, efficient con...
BusyContacts is a contact manager for OS X that makes creating, finding, and managing contacts faster and more efficient. It brings to contact management the same power, flexibility, and sharing... Read more
MarsEdit 3.7.10 - Quick and convenient b...
MarsEdit is a blog editor for OS X that makes editing your blog like writing email, with spell-checking, drafts, multiple windows, and even AppleScript support. It works with with most blog services... Read more
BusyCal 3.1.4 - Powerful calendar app wi...
BusyCal is an award-winning desktop calendar that combines personal productivity features for individuals with powerful calendar sharing capabilities for families and workgroups. Its unique features... Read more
VirtualBox 5.1.14 - x86 virtualization s...
VirtualBox is a family of powerful x86 virtualization products for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers... Read more
Bookends 12.7.8 - Reference management a...
Bookends is a full-featured bibliography/reference and information-management system for students and professionals. Bookends uses the cloud to sync reference libraries on all the Macs you use.... Read more
VirtualBox 5.1.14 - x86 virtualization s...
VirtualBox is a family of powerful x86 virtualization products for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers... Read more
FileZilla 3.24.0 - Fast and reliable FTP...
FileZilla (ported from Windows) is a fast and reliable FTP client and server with lots of useful features and an intuitive interface. Version 3.24.0: New The context menu for remote file search... Read more

Super Mario Run dashes onto Android in M...
Super Mario Run was one of the biggest mobile launches in 2016 before it was met with a lukewarm response by many. While the game itself plays a treat, it's pretty hard to swallow the steep price for the full game. With that said, Android users... | Read more »
WarFriends Beginner's Guide: How to...
Chillingo's new game, WarFriends, is finally available world wide, and so far it's a refreshing change from common mobile game trends. The game's a mix of tower defense, third person shooter, and collectible card game. There's a lot to unpack here... | Read more »
Super Gridland (Entertainment)
Super Gridland 1.0 Device: iOS Universal Category: Entertainment Price: $1.99, Version: 1.0 (iTunes) Description: Match. Build. Survive. "exquisitely tuned" - Rock Paper Shotgun No in-app purches, and no ads! | Read more »
Red's Kingdom (Games)
Red's Kingdom 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Mad King Mac has kidnapped your father and stolen your golden nut! Solve puzzles and battle goons as you explore and battle your... | Read more »
Turbo League Guide: How to tame the cont...
| Read more »
Fire Emblem: Heroes coming to Google Pla...
Nintendo gave us our first look at Fire Emblem: Heroes, the upcoming mobile Fire Emblem game the company hinted at last year. Revealed at the Fire Emblem Direct event held today, the game will condense the series' tactical RPG combat into bite-... | Read more »
ReSlice (Music)
ReSlice 1.0 Device: iOS Universal Category: Music Price: $9.99, Version: 1.0 (iTunes) Description: Audio Slice Machine Slice your audio samples with ReSlice and create flexible musical atoms which can be triggered by MIDI notes or... | Read more »
Stickman Surfer rides in with the tide t...
Stickson is back and this time he's taken up yet another extreme sport - surfing. Stickman Surfer is out this Thursday on both iOS and Android, so if you've been following the other Stickman adventures, you might be interested in picking this one... | Read more »
Z-Exemplar (Games)
Z-Exemplar 1.4 Device: iOS Universal Category: Games Price: $3.99, Version: 1.4 (iTunes) Description: | Read more »
5 dastardly difficult roguelikes like th...
Edmund McMillen's popular roguelike creation The Binding of Isaac: Rebirth has finally crawled onto mobile devices. It's a grotesque dual-stick shooter that tosses you into an endless, procedurally generated basement as you, the pitiable Isaac,... | Read more »

Price Scanner via MacPrices.net

Twelve South Releases RelaxedLeather Cases fo...
Inspired by the laid-back luxury of burnished leather boots and crafted in rich tones of taupe, herb and marsala, RelaxedLeather cases deliver smart, easy protection for the iPhone 7. Each genuine... Read more
Week’s Best Deal: New 2016 13-inch 2.0GHz Mac...
Amazon has the new 2016 13″ 2.0GHz non-Touch Bar MacBook Pros on sale for a limited time for $225 off MSRP including free shipping: - 13″ 2.0GHz MacBook Pro, Space Gray (MLL42LL/A): $1274.99 $225 off... Read more
Back in stock: Apple refurbished Mac minis fr...
Apple has Certified Refurbished Mac minis available starting at $419. Apple’s one-year warranty is included with each mini, and shipping is free: - 1.4GHz Mac mini: $419 $80 off MSRP - 2.6GHz Mac... Read more
Apple Ranked ‘Most Intimate Brand’
The top ranked ‘”intimate” brands continued to outperform the S&P and Fortune 500 indices in revenue and profit over the past 10 years, according to MBLM’s Brand Intimacy 2017 Report, the largest... Read more
B-Eng introduces SSD Health Check for Mac OS
Fehraltorf, Switzerland based independant Swiss company- B-Eng has announced the release and immediate availability of SSD Health Check 1.0, the company’s new hard drive utility for Mac OS X. As the... Read more
Apple’s Education discount saves up to $300 o...
Purchase a new Mac or iPad using Apple’s Education Store and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free: -... Read more
4-core 3.7GHz Mac Pro on sale for $2290, save...
Guitar Center has the 3.7GHz 4-core Mac Pro (MD253LL/A) on sale for $2289.97 including free shipping or free local store pickup (if available). Their price is a $710 savings over standard MSRP for... Read more
128GB Apple iPad Air 2, refurbished, availabl...
Apple has Certified Refurbished 128GB iPad Air 2s WiFis available for $419 including free shipping. That’s an $80 savings over standard MSRP for this model. A standard Apple one-year warranty is... Read more
13-inch 2.7GHz Retina MacBook Pro on sale for...
B&H Photo has the 2015 13″ 2.7GHz/128GB Retina Apple MacBook Pro on sale for $100 off MSRP. Shipping is free, and B&H charges NY tax only: - 13″ 2.7GHz/128GB Retina MacBook Pro (MF839LL/A): $... Read more
Laptop Market – Flight To Quality? – The ‘Boo...
Preliminary quarterly PC shipments data released by Gartner Inc. last week reveal an interesting disparity between sales performance of major name PC vendors as opposed to that of less well-known... Read more

Jobs Board

*Apple* MAC Infrastructure Engineer - InnoCo...
Summary: Responsible for all aspects of Apple Desktop hardware. This includes research, design, test, and deploy technologies being researched by the desktop Read more
*Apple* & PC Desktop Support Technician...
Apple & PC Desktop Support Technician job in Manhattan, NY Introduction: We have immediate job openings for several Desktop Support Technicians with one of our most Read more
Senior Workstation Administrator - *Apple*...
…with extraordinary HR. QualificationsJOB SUMMARY/OVERVIEWThe Senior Workstation Administrator - Apple supports the mission of TriNet by providing advanced level Read more
Intermediate *Apple* macOS Systems Integrat...
**Position Summary:** SC3 is actively seeking an Intermediate Apple macOS systems integration administrator that will be responsible for providing Apple Mac Read more
*Apple* & PC Desktop Support Technician...
Apple & PC Desktop Support Technician job in Los Angeles, CA Introduction: We have immediate job openings for several Desktop Support Technicians with one of our Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.