How to dump multiple subversion repositories at once on various OSs

How do I make a dump of a number of subversion repositories - with all repositories residing in one folder - on various operating systems (Linux shells, Windows 9x/Vista/XP/Server, etc.)?

I'll post an answer that works on Windows Server 2003 - but maybe there's a more elegant one for that, too.

(Additional background to the question here.)

Bash:

#!/bin/bash
REPO_BASE=...
SVNADMIN=...

cd "$REPO_BASE"
for f in *; do
    test -d "$f"  &&  $SVNADMIN dump "$f" >"$f.svn"
done

(test -d makes sure to dump directories only)

This works on Windows 2003 server and is likely to work on other Windows OS's, too. It looks for any sub-directories in the specified "repos" directory and tries to run a svnadmin dump on each and every one of them. It creates dump files named (reponame).svn

dump_repos.bat

cd \my\subversion\repos
dir /A:D /B> dirs.tmp
FOR /F %%i IN (dirs.tmp) DO (
 "C:\path\to\subversion\bin\svnadmin.exe" dump %%i > %%i.svn
)