first-checkout.sh

#!/bin/bash

if test -z "$1"; then
  case `uname -s` in
    "Linux")
      os=unix
      ;;
    "Darwin")
      os=mac
      ;;
    *)
      echo "You didn't specify an OS (mac, win, unix, or android), and I can't figure it out from 'uname -s'" 1>&2
      exit 1
      ;;
  esac
else
  os=$1
fi

git config target.os $os
git checkout --force HEAD
git config -f .gitmodules --get-regexp '.os$' "(all|$os)" |
sed 's/^submodule\.\(.*\)\.os .*$/\1/' |
while read submodule; do
  git config submodule.$submodule.update checkout
  (cd $submodule && git checkout --force HEAD)
done
git submodule init
git submodule update