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Using CVS (part 1) |
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================== |
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|
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tdb1, 18/10/2000 |
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|
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Overview |
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-------- |
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CVS means "Concurrent Versioning System" and is used to keep |
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version control on plain text files - usually source code, |
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or html, but can be anything that has a plain text |
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structure. It can store binaries, but doesn't offer the |
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same version comparison features for obvious reasons. |
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|
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CVS also offers many features for group working, and doesn't |
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lock the files when someone starts editing them. Instead it |
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works by each user having their own "checked out" local copy |
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of the source code (or a portion of it). The user then works |
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on this code until they are happy with it, then runs an |
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update command. This checks to see if someone else has |
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updated the version in the repository, and if so brings |
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their changes down into the users local copy. This can cause |
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conflicts if both users change the same bit, but this |
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shouldn't really happen - unless group communication is |
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lacking. CVS will do it's best to merge these new changes |
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in, but occasionaly it will need help from the user. This is |
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just a case of reviewing the file with conflicts and |
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manually resolving them. When CVS is happy that any updates |
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in the repository have been merged it will allow a commit. |
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This puts the users changes into the repository for all to |
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access. |
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|
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In essence, that's CVS. Checkout, update, commit. That's all |
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there really is to it. |
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|
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I think CVS would be very beneficial in writing the code for |
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our project for two reasons. Firstly CVS will help us to |
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maintain a control on all of our code for QA purposes, and |
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make it easy for us to keep track of our "phases". We can |
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tag the code at the end of each phase, and then continue |
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development. At the same time, another group member could be |
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testing the code at the tagged point. Finally, the group |
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work features make it ideal for this situation. |
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|
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CVS Repository Structure |
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------------------------ |
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I am proposing the following structure for the CVS |
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Repository. I suggest that we keep it the same from the word |
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go, although we can add more into the hierachy it's not |
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usually a good idea to move things around. |
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|
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ROOT |
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documentation |
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minutes |
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misc |
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papers |
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plan |
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presentation |
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specification |
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user |
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experimental |
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client |
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host |
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misc |
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server |
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misc |
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source |
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client |
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host |
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misc |
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server |
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web |
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client |
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website |
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cgi-bin |
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www |
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|
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We may need to expand that a bit, but it's a start. |
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|
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Setting up CVS on Raptor |
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------------------------ |
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Setting up CVS on raptor to use our "repository" takes a bit |
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of effort. This is because the cs-sysadmin guys have been |
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setting up CVS to run from marble, but it's not ready yet. |
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All we have to do is override some of their default |
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environment variables. Right, so add the following lines to |
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your .cshrc file (presuming you are using csh, which I think |
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you are). |
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|
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unsetenv CVSROOT |
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unsetenv CVSREAD |
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unsetenv CVS_RSH |
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unsetenv CVSIGNORE |
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setenv CVSROOT /usr/local/proj/co600_10/cvs |
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|
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A quick explanation of what this actually means. Firstly the |
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CVSROOT is the root directory of the CVS repository. I've |
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set it up as a directory called 'cvs' in our project space. |
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Next the CVS_RSH variable tells CVS to use something like |
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SSH, which we don't need to do locally. CVSREAD makes CVS |
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mark the files it checks-out be read-only, which is meant to |
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make you use the cvs edit command... but it's just a |
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complete pain in the arse. Last of all CVSIGNORE tells CVS |
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not to add certain files, but I think we've got enough sense |
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to be able to do that ourselves... but by all means leave |
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that line out if you feel happier. |
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|
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Setting up CVS on a Public PC (with WinCVS) |
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------------------------------------------- |
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WinCVS is (obviously) a Windows frontend to CVS. The command |
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line thing is far easier to use if you're doing stuff |
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directly on raptor (or any other unix box), but under |
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windows it's nice to be able to get at files much more |
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easily. It's also got the familiar "point-n-click" style |
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interface, but I personally find that confusing. |
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WinCVS can be found at the following location; |
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\\drogo\packages\gnu\wincvs\wincvs.exe |
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It's not under Install Packages, so you might want to make |
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your own shortcut on the desktop, which is what I've done. |
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Setting up is easy. First map a drive to \\raptor\grproj (go |
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for grproj to help keep the permissions happy). Then when |
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the preferences pop up bung in m:\co600_10\cvs (assuming you |
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used m: like I did...) and select "Local mounted directory" |
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under Authentication. The only other bits to change are |
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unticking the "Checkout read-only" under Globals (it's just |
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a damn pain), and under WinCVS you might want to change the |
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"HOME folder" to your Z: drive. |
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|
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Then you're ready to go with doing usual CVS stuff. Oh, it |
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took me ages to figure how to change which drive/directory |
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is viewed in the main windows... it's hidden at the bottom |
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of the View menu. |
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|
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Finally, it might be possible to get it working with SSH |
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straight onto raptor, but I'm not sure of the exact process, |
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and even if it'll work. I may add this as an errata in part2 |
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of this documentation. |
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|
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Setting up CVS from off campus |
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------------------------------ |
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Using CVS from off campus is much trickier. We have no |
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"proper" CVS facilities on raptor for remote access (it can |
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run a server specifically for this task). However, as the |
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command line CVS will make use of SSH we can connect through |
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the firewall. This is fine if you have a Unix box at home, |
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but I'm not sure (again) if this will work from Windows. |
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From any Unix box (that has SSH and CVS installed) you just |
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need to setup the following environment variables. These are |
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best put in a file such as .cshrc (for the csh shell). |
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|
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CVS_RSH = |
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ssh |
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CVSROOT = |
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:ext:user@raptor.ukc.ac.uk:/usr/local/proj/co600_10/cvs |
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|
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Every shell has it's own way of setting up environment |
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variables, for example csh using the setenv command. Consult |
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the man pages for more details. |
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With this done you can use the command line facilities as |
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usual, and you will be prompted for your raptor password |
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each time a connection is made. |
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How to use CVS |
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-------------- |
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There are three main CVS operations that you'll use on a |
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regular basis; checkout, update and commit. Then there's the |
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smaller commands such as add, delete, and export. I'll |
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describe them, then give an example. This all assumes you've |
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setup the CVSROOT environment variable as described above. |
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These commands are for the command line version of CVS, but |
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the ideas can be applied to any version, including WinCVS. |
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A full list of commands can be found by typing; |
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cvs --help-commands |
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A quick mention of the version numbers first. Each file has |
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a unique version number starting at 1.1 and incrementing to |
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1.2, 1.3 and so on. It never becomes 2.x, unless you |
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manually change it. These version numbers are independant |
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for every single file, and have no overall bearing on any |
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"release versions" that go out to the public. |
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Firstly, the 'checkout' command. This extracts a copy of a |
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section of the CVS Repository to a local working copy. All |
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work (editing) is then carried out on this local copy. The |
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local copy can be changed, completely deleted, or |
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whatever... it'll have no effect on the database. The |
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command has the following format; |
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cvs checkout <module> |
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eg. |
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cvs checkout source/server |
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This would extract a copy of all the files in server/source |
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and all subdirectories below this. Note that CVS control |
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files will be created in 'CVS' subdirectories all over the |
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place, they're best ignored. |
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|
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Next the 'update' command. This command ensures that the |
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local copy is up-to-date with the database. If the checkout |
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was done a few days ago it's possible someone else may have |
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updated something in the main repository since the original |
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checkout. After issuing the update the local copy will be |
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updated. The command is very simple; |
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cvs update |
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The exception to this is if the user has changed the local |
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copy in some way. In this case the update still takes place, |
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but any changes are merged into the local copy. No updates |
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are sent to the repository, this is important to remember! |
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This could of course cause problems if the update on the |
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repository and the local update are on the same bit of code. |
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Usually CVS can merge updates, but in this instance it will |
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give a conflict error and the user will have to manually |
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resolve them. This is a simple case of checking the code the |
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problem areas will be marked out. After the conflicts have |
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been resolved another update could be done to verify it's |
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all OK. |
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|
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The update command also lets you know the state of files. If |
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it puts an 'M' next to a file (when it lists them) it means |
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you've modified it. If it's got a '?' it means the file is |
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new or not part of the CVS (you have to add new files). A |
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'C' means a conflicting file, and I think maybe 'A' means |
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the file is scheduled to be added. There are probably |
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others, check "man cvs" :) |
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Right, the last main command is 'commit'. This puts local |
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changes back into the repository and updates the version |
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number. You should run an update first, though, and commit |
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will complain if you haven't done when you need to. You will |
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need to enter a comment, and it's good practice to describe |
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roughly the reason for the commit - it helps keep a good |
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audit trail, and lets other users know why you did what you |
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did. In Unix it'll probably load up vi, which is ugly... I |
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think if you change the EDITOR enviroment variable you can |
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set it to use pico. The commit command is as easy as; |
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cvs commit |
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That's all there is to the everyday CVS commands. Next the |
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occasional commands. Now on to the less used ones. |
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|
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Lets start with the 'add' command. Say you've done a |
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checkout of source/server and you've added a file called |
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main.java into the directory. Now lets add it to the |
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repository. |
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cd source/server |
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cvs add main.java |
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The add command will tell you that it's scheduled to be |
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added at the next commit. Simply run an update then commit |
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for the file to be added. |
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|
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The 'remove' command works in a similar way I think. I'm not |
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sure whether you have to delete the file first, you'll have |
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to try it. Again you'll need to update then commit. A note |
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about deleted. The file obviously won't be deleted |
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completely, that would defeat the point in a versioning |
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system. Instead it's moved to an Attic subdirectory in the |
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CVS so you can still review it's revisions in the future, |
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and even resurrect it. |
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|
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Next there's the 'release' command. This is used as a tidy |
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way of cleaning up the local files when you've finished with |
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them. To remove the above example you'd do the following; |
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cvs release source/server |
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This will ensure that you don't accidently delete any local |
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changes by informing you first of any non-commited files. If |
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you add the -d switch it will actually delete the files too; |
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cvs release -d source/server |
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This is much safer than typing "rm..." :) |
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|
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Finally, the 'export' command. This has almost the same |
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effect as the checkout command, but it doesn't create any of |
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the CVS control files. The aim of this command is to extract |
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sources for public release, so you can zip them up and send |
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them out to the client. For example; |
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|
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cvs export source |
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tar -cvf source.tar source |
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gzip -v9 source.tar |
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|
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That's just about it for basic CVS. I'll probably produce |
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another document on tagging at some point in the future. |
