What is the best way to choose a random file from a directory in a shell script?

Here is my solution in Bash but I would be very interested for a more portable (non-GNU) version for use on Unix proper.

dir='some/directory'
file=`/bin/ls -1 "$dir" | sort --random-sort | head -1`
path=`readlink --canonicalize "$dir/$file"` # Converts to full path
echo "The randomly-selected file is: $path"

Anybody have any other ideas?

Edit: lhunath makes a good point about parsing ls. I guess it comes down to whether you want to be portable or not. If you have the GNU findutils and coreutils then you can do:

find "$dir" -maxdepth 1 -mindepth 1 -type f -print0 \
  | sort --zero-terminated --random-sort \
  | sed 's/\d000.*//g/'

Whew, that was fun! Also it matches my question better since I said "random file". Honsetly though, these days it's hard to imagine a Unix system deployed out there having GNU installed but not Perl 5.