[bash] Remove all files except some from a directory

Since no one yet mentioned this, in one particular case:

OLD_FILES=`echo *`
... create new files ...
rm -r $OLD_FILES

(or just rm $OLD_FILES)

or

OLD_FILES=`ls *`
... create new files ...
rm -r $OLD_FILES

You may need to use shopt -s nullglob if some files may be either there or not there:

SET_OLD_NULLGLOB=`shopt -p nullglob`
shopt -s nullglob
FILES=`echo *.sh *.bash`
$SET_OLD_NULLGLOB

without nullglob, echo *.sh *.bash may give you "a.sh b.sh *.bash".

(Having said all that, I myself prefer this answer, even though it does not work in OSX)