Create/Mount Disk Image to use Steam for Mac, preserving your existing case-sensitive Mac file system

#!/bin/sh
# For people who like case-sensitive filesystems and games.
# It should still work for people who don't care what case their filesystem is.

# Create a sparse bundle disk image to house an insensitive filesystem.
# This creates a 10GiB disk image that will please Steam. Don't worry -- those
# 10GiB will only be allocated when you actually start getting games.
echo ">>> Creating disk image."
VOLUME=`hdiutil create -size 10g -type SPARSEBUNDLE -fs HFS+J \
                -volname Steam -layout NONE -attach Steam \
      | egrep -o '/Volume.+'`

# Change to the disk image's directory and begin working in there.
cd ${VOLUME}

# Download the latest Steam binary for Mac OS X.
echo ">>> Discovering Steam's location."
LOCATION="http://store.steampowered.com/public/client/"
# Discover the latest binary's filename.
FILE=`curl -# ${LOCATION}steam_client_osx \
    | grep -A 3 \"steam_osx\" \
    | egrep -o 'steam_osx.zip.[^"]+'`
echo ">>> Downloading Steam."
curl -# -L ${LOCATION}${FILE} -o steam_osx.zip

# Extract and sort out the file permissions.
unzip -d Steam.app steam_osx.zip > /dev/null
rm -fv steam_osx.zip
chmod -vv 0755 Steam.app/osx32/steam Steam.app/steam.sh

# Check to see if Steam has been run before and move directories to new
# location. If not, create the various directories required.
APPSUPPORT="${HOME}/Library/Application Support/Steam"
VOLAPPSUPPORT="${VOLUME}/Application Support"
if [ -d "${APPSUPPORT}" ]; then
    echo ">>> Moving ${APPSUPPORT} to ${VOLUME}/Application Support."
    cp -avX "${APPSUPPORT}" "${VOLAPPSUPPORT}"
    echo ">>> Sending ${APPSUPPORT} to the Trash."
    osascript -e "tell application \"Finder\"
                      delete POSIX file \"${APPSUPPORT}\"
                  end tell"
fi
if [ ! -d "${VOLAPPSUPPORT}" ]; then
    echo ">>> Creating ${VOLAPPSUPPORT}."
    mkdir -pv "${VOLAPPSUPPORT}"
fi

STEAMCONTENT="${HOME}/Documents/Steam Content"
VOLSTEAMCONTENT="${VOLUME}/Steam Content"
if [ -d "$STEAMCONTENT" ]; then
    echo ">>> Copying ${STEAMCONTENT} to ${VOLUME}/Steam Content."
    cp -avX "${STEAMCONTENT}" "${VOLSTEAMCONTENT}"
    echo ">>> Sending ${STEAMCONTENT} to the Trash."
    osascript -e "tell application \"Finder\"
                      delete POSIX file \"${STEAMCONTENT}\"
                  end tell"
fi
if [ ! -d "${VOLSTEAMCONTENT}" ]; then
    echo ">>> Creating ${VOLSTEAMCONTENT}."
    mkdir -pv "${VOLSTEAMCONTENT}"
fi

# Link to the disk image.
ln -fnsv "${VOLAPPSUPPORT}" "${APPSUPPORT}"
ln -fnsv "${VOLSTEAMCONTENT}" "${STEAMCONTENT}"

# Attempt to run Portal (store ID is 400).
osascript -e 'tell application "Finder" to open location "steam://run/400/"'