How to ignore folder without removing it from my repository

repository, svn

Solution

$ cd /path/to/app/tmp
$ svn propset svn:ignore '*' .
$ cd /path/to/app/cache
$ svn propset svn:ignore '*' .

EDIT: Here's the steps if you already previously committed

$ cd /path/to/app/tmp
$ svn st
M slkdjfag.jpg
M gasgsag.png
. #bunch of M's

$ svn rm * --force
$ svn ci -m'trunk: cleaning up tmp directory'
$ svn propset svn:ignore '*' .
$ touch a
$ svn st // shouldn't output anything

Problem

I have this tmp/ and cache/ directories, that keep generating files that don't need to be commited. How can I set it so svn ignores them, but doesn't delete them or remove them from the repository, they are needed for the site to work.

Original source