Upgrade all the casks installed via Homebrew Cask

There is now finally an official upgrade mechanism for Homebrew Cask (see Issue 3396 for the implementation)! To use it, simply run this command:

brew upgrade --cask

However this will not update casks that do not have versioning information (version :latest) or applications that have a built-in upgrade mechanism (auto_updates true). To reinstall these casks (and consequently upgrade them if upgrades are available), run the upgrade command with the --greedy flag like this:

brew upgrade --cask --greedy

To get outdated:

brew outdated --cask --greedy --verbose

It is possible to list the installed casks with:

brew cask list

And force the re-installation of a cask with:

brew cask install --force CASK_NAME

So piping the output of the first command into the second, we update all the casks:

brew cask list | xargs brew cask install --force

homebrew-cask-upgrade

I think this is by far the best solution to upgrade the casks.
source: https://github.com/buo/homebrew-cask-upgrade

Installation & usage

brew tap buo/cask-upgrade
brew update
brew cu

(Optional) Force upgrade outdated apps including the ones marked as latest:

brew cu --all