brew-cask-check-updates

brew-cask-check-updates.bash

for cask in $(brew cask list -1); do
  echo -n "${cask} : ";
  caskLatest=$(brew cask info $cask | head -1 | awk -F: '{print $2}' | tr -d '[[:space:]]');
  caskCurrentDir=$(brew cask info $cask | grep -e "^$(brew --prefix).*/${cask}/"| head -1| awk '{print $1}');
  [ ! -d $(dirname ${caskCurrentDir})/${caskLatest} ] && echo "outdated : ("$(basename ${caskCurrentDir})" -> "${caskLatest}")" || echo "current";
done

This is a type of q'n'dirty "workaround"
to update all outdated casks e.g.:
. ./brew-cask-check-updates.bash | awk -F: '{if ($2 ~ "outdated") print $1}' | xargs brew cask reinstall

other 'hacks' found:
https://gist.github.com/atais/9c72e469b1cbec35c7c430ce03de2a6b
or
https://github.com/buo/homebrew-cask-upgrade
via

• http://apple.stackexchange.com/questions/190072
• http://stackoverflow.com/questions/31968664

see right place to discuss the clean solution: Homebrew/homebrew-cask#29301