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Subversion

Kate HedstromApril 2007

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Version Control Software

• System for managing source files– For groups of people working on the same code

– When you need to get back last week’s version

• In the old days, there was SCCS and RCS for file-wise management

• Then came CVS– Works with whole directory trees– Has a network option for remote access

• Newest is SVN, which attempts to fix the shortcomings in CVS

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Getting Started With SVN

• Tell it where the archive is with a URL:

• Mine is in nanook’s /archive, visible to Sun and iceflyer

• For a new archive:

file:///local/path orhttp://host/path

% svnadmin create /local/path

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Main svn commands

• import - bring sources into the repository

• checkout - get sources out of the repository

• commit - check in changes• update - get changes from repository• status - find out which files would change on commit

• diff - find out what changed• help

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Example

• The svn people advise setting up a directory tree with subdirectories– trunk– tags– branches

• Your actual code goes in trunk

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% ls /tmp/cppbranches tags trunk# import whole directory% svn import /tmp/cpp \ file:///local/path -m “initial import”% rm -rf /tmp/cpp# want to be working in checked-out copy% svn checkout \ file:///local/path/cpp/trunk cpp% cd cpp[make some changes]% svn commit

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# on iceflyer% svn checkout <URL> roms% cd roms[make some changes]% svn commit

# on cygnus% svn checkout …% cd roms% svn update% make

Coordination

• Coordinate code on multiple systems• Coordinate between multiple programmers

• Can be common version or different branches

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Updates

• An update when two people have changed things can involve:– No conflict because changes are in different

places– Conflict because two different changes to the

same region in the code

• If there is a conflict this must be resolved by human intervention

• One option is to revert (undo)

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Other svn commands• add - add a new file or directory to svn control

• delete - no longer need a file• move - rename a file or move to new location

• merge - merge changes from another branch

• info - find URL used• copy - make branches and tags• switch - switch working directory to a different branch

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Revision Numbers

• svn uses a database to store the files• The whole project as one revision number across the whole project to describe that snapshot

• Can see the numbers with “svn log”• This is different from CVS, which keeps a different number for each file (uses filewise RCS for repository)

• Every commit creates a new revision number

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• Branch can be just for one or a few files or the whole ROMS tree

Branches

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Tags

• Tags are handled like branches• Create a working version that goes together and make a branch in the tags directory with the name of the tag (release_1.0, say)

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ROMS Example

• ROMS comes from a read-only repository:

svn checkout <URL> hernan_roms• Make own repository where that version is the trunk– Copy it to another location without the .svn files– Import it into your repository

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• Now make a branch for your version: svn copy <URL1> <URL2>• These have to be in the same repository

• It is currently a copy of the main ROMS code - edit it with your changes and check it back in

svn checkout <URL2> Edit… svn commit

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• So, Hernan has made some changes, what now?

• Go to your copy of his code from his repository:

svn update• Make note of files that were added and deleted

• Copy to the trunk part of your repository:

tar cvf - --exclude .svn | (cd ../roms_trunk; tar xvf -)

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• In your trunk directory, add and delete the files you noted before:

svn add new files… svn delete old files…• Check status, then check in: svn status svn commit• Make note of the version number

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• Doing the actual merge - in the directory for your branch (URL2):

svn merge -r 41:45 <URL1>• Resolve conflicts, if any• Check in the update, making note of the revision numbers and <URL1>

svn ci -m “merge from -r 41:45 <URL1>”

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ROMS Summary

• Each directory has .svn files pointing to its URL

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Conflicts

• If there is a conflict, svn will provide you with four files:– The original file (filename.mine)– The older file from the trunk (filename.r41)– The newer file from the trunk (filename.r45)– A merge attempt (filename)

• The merge failures will look something like:

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Clean code before <<<<<<< .mine My code ======= New code >>>>>>> .r45 Clean code after• Once you’ve cleaned up the mess, tell svn you’re ready:

svn resolved filename• This will cause svn to delete the extra files and allow a commit to take place

• You can instead toss your changes with: svn revert filename

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Learn more

• Version Control with Subversion, by Collins-Sussman et al., 2004, O’Reilly

• Online at http:svnbook.red-bean.com/• svn help