Hmm, not sure I agree with Nick re tag being similar to a branch. A tag is just a marker
Trunk would be the main body of development, originating from the start of the project until the present.
Branch will be a copy of code derived from a certain point in the trunk that is used for applying major changes to the code while preserving the integrity of the code in the trunk. If the major changes work according to plan, they are usually merged back into the trunk.
Tag will be a point in time on the trunk or a branch that you wish to preserve. The two main reasons for preservation would be that either this is a major release of the software, whether alpha, beta, RC or RTM, or this is the most stable point of the software before major revisions on the trunk were applied.
In open source projects, major branches that are not accepted into the trunk by the project stakeholders can become the bases for forks -- e.g., totally separate projects that share a common origin with other source code.
The branch and tag subtrees are distinguished from the trunk in the following ways:
Subversion allows sysadmins to create hook scripts which are triggered for execution when certain events occur; for instance, committing a change to the repository. It is very common for a typical Subversion repository implementation to treat any path containing "/tag/" to be write-protected after creation; the net result is that tags, once created, are immutable (at least to "ordinary" users). This is done via the hook scripts, which enforce the immutability by preventing further changes if tag is a parent node of the changed object.
Subversion also has added features, since version 1.5, relating to "branch merge tracking" so that changes committed to a branch can be merged back into the trunk with support for incremental, "smart" merging.
Create a users file (i.e. users.txt) for mapping SVN users to Git:
user1 = First Last Name <email@address.com>
user2 = First Last Name <email@address.com>
...
You can use this one-liner to build a template from your existing SVN repository:
svn log -q | awk -F '|' '/^r/ {gsub(/ /, "", $2); sub(" $", "", $2); print $2" = "$2" <"$2">"}' | sort -u > users.txt
SVN will stop if it finds a missing SVN user, not in the file. But after that, you can update the file and pick up where you left off.
Now pull the SVN data from the repository:
git svn clone --stdlayout --no-metadata --authors-file=users.txt svn://hostname/path dest_dir-tmp
This command will create a new Git repository in dest_dir-tmp and start pulling the SVN repository. Note that the "--stdlayout" flag implies you have the common "trunk/, branches/, tags/" SVN layout. If your layout differs, become familiar with --tags, --branches, --trunk options (in general git svn help).
All common protocols are allowed: svn://, http://, https://. The URL should target the base repository, something like http://svn.mycompany.com/myrepo/repository. The URL string must not include /trunk, /tag or /branches.
Note that after executing this command it very often looks like the operation is "hanging/frozen", and it's quite normal that it can be stuck for a long time after initializing the new repository. Eventually, you will then see log messages which indicate that it's migrating.
Also note that if you omit the --no-metadata flag, Git will append information about the corresponding SVN revision to the commit message (i.e. git-svn-id: svn://svn.mycompany.com/myrepo/<branchname/trunk>@<RevisionNumber> <Repository UUID>)
If a user name is not found, update your users.txt file then:
cd dest_dir-tmp
git svn fetch
You might have to repeat that last command several times, if you have a large project until all of the Subversion commits have been fetched:
git svn fetch
When completed, Git will checkout the SVN trunk into a new branch. Any other branches are set up as remotes. You can view the other SVN branches with:
git branch -r
If you want to keep other remote branches in your repository, you want to create a local branch for each one manually. (Skip trunk/master.) If you don't do this, the branches won't get cloned in the final step.
git checkout -b local_branch remote_branch
# It's OK if local_branch and remote_branch are the same names
Tags are imported as branches. You have to create a local branch, make a tag and delete the branch to have them as tags in Git. To do it with tag "v1":
git checkout -b tag_v1 remotes/tags/v1
git checkout master
git tag v1 tag_v1
git branch -D tag_v1
Clone your GIT-SVN repository into a clean Git repository:
git clone dest_dir-tmp dest_dir
rm -rf dest_dir-tmp
cd dest_dir
The local branches that you created earlier from remote branches will only have been copied as remote branches into the newly cloned repository. (Skip trunk/master.) For each branch you want to keep:
git checkout -b local_branch origin/remote_branch
Finally, remove the remote from your clean Git repository that points to the now-deleted temporary repository:
git remote rm origin
Best Answer
I've just tried a brief experiment with TortoiseSVN:
Creating the test repositories
At this stage you will be in the state of having created your local 'branch' in a new repository. The last two steps are all you need for an existing project.
To simulate some changes to the original repo, modify the text file in co1 and commit the changes.
Merging Changes
Now, to create your own working copy, check out rep2 into co2.
We should be ready to try merging from rep1 into co2.
Open the merge dialog for co2 and point it at rep1.
For the 'from' revision select the revision at which you exported your copy (in this case revision 1), or the revision that you last updated your local copy to.
For the 'to' revision select the HEAD or the latest update you want to apply.
Results
This seems to work as expected, with the modifications from rep1 being applied to the working copy of rep2 in co2. These then need to be committed back to your local repository.