Check for updates to all Homebrew Cask applications and upgrade them (workaround until cask gets a built-in mechanism for this)

cask-upgrade.sh

#!/usr/bin/env bash

fetch() {
    echo "Removing brew cache"
    local cache=$(brew --cache) 
    rm -rf "$(brew --cache)"
    mkdir "$cache"
    mkdir "$cache/Casks"
    echo "Running brew update" 
    brew update 
}

update() {
    casks=( $(brew cask list) )
    caskroom=$(brew --prefix)/Caskroom

    echo
    echo "Checking for updates"
    echo

    local UPDATES_FOUND=0
    for cask in ${casks[@]}
    do
        current="$(brew cask info $cask | sed -n '1p' | sed -n 's/^.*: \(.*\)$/\1/p')"
        installed=( $(ls -Art $caskroom/$cask/ | egrep 'latest|(\d.*)' | tail -n 1))
        if [ "$installed" != "$current" ]; then
            echo "$cask ($installed -> $current)"
            UPDATES_FOUND=1
        fi
    done

    if [ "$UPDATES_FOUND" -eq 0 ]; then
        echo "Nothing to update"
        return
    fi

    echo
    echo "Install updates now?"
    
    select yn in "Yes" "No"; do
        case $yn in
            "Yes") echo "Updating outdated casks"; break;;
            "No") echo "Upgrade cancelled" ;return;;
            *) echo "Please choose 1 or 2";;
        esac
    done

    for cask in ${casks[@]}
    do
        current="$(brew cask info $cask | sed -n '1p' | sed -n 's/^.*: \(.*\)$/\1/p')"
        installed=( $(ls -Art $caskroom/$cask/ | egrep 'latest|(\d.*)' | tail -n 1))
        if [ "$installed" != "$current" ]; then
            rm -rf $caskroom/$cask/$installed
            brew cask install $cask --force
        fi
    done
}

fetch
update

Sample output:

Removing brew cache
Running brew update
Already up-to-date.

Checking for updates

intellij-idea (15.0.3 -> 2016.1)
java (1.8.0_74-b02 -> 1.8.0_77-b03)
rstudio (0.99.878 -> 0.99.893)
sketch (3.5.2 -> 3.6.1)
skim (1.4.17 -> 1.4.18)
visual-studio-code (45d69357c9eb068dd8e624f5b0fe461cd2078d88 -> 0.10.11,f291f4ad600767626b24a4b15816b04bee9a3049)
xamarin-studio (5.10.2.56-0 -> 5.10.3.27-0)

Install updates now?
1) Yes
2) No