I tried using svn ci dir/a dir/b -m "my comment" but this doesn't work. I also used svn ci dir/a/* dir/b/* -m "my comment" and it too doesn't work.
I know you can specify multiple files, but how can I tell subversion to check in all modified files in these folders? I mainly want to do this so that all my changes get in on one revision. I can checkin one directory at a time, but this ends up giving me different revisions for each directory..
svn add dir/a
svn add dir/b
svn commit
Though, more likely, you're thinking:
svn add dir/*
svn commit
I think you only have 1 option: check in the containing directory - the one that has both these as subdirs.
If they're not organised like that already (ie they're both top-level directories in the repo), then there's not a lot you can do - the svn commands work on a single directory only.
This is easy if you check-out from a higher level folder for where a and b are. So if your working copy is "dir" and a and b have changes, commit "dir" to commit changes to both. I do this all of the time.
Edit:
To commit more than one folder, you will need for them to be in the same working copy.
If you are worried about having too much to process, you could try a sparse checkout with only the folders you need, and then you could just commit the base directory or the subdirectories as needed without the overhead of the other projects.
You may need to specify what does "but this doesn't work" mean because it works fine here:
D:\Projects>svn commit -m 'test1' test\aaa "test\aaa bbb ccc"
Sending test\aaa\aaa222\xxx.txt
Sending test\aaa bbb ccc\aaa.txt
Transmitting file data ..
Committed revision 8.
D:\Projects>
Consider using svn:externals property for checking out part of the repository. You can pick and choose which directories to get, then commit to multiple destinations in a single step. We've been using this approach for a while with great success.