gistfile1.sh

function _bundle_exec() {
  if [ -e Gemfile ]; then
    grep -q "$1" "Gemfile.lock"
    if [[ "$1" == "ruby" || $? -eq 0 ]]; then
      echo "bundle exec $@"
      bundle exec $@
      return
    fi
  fi

  $@
}

for cmd in ruby rails rake rspec
do
  alias $cmd="_bundle_exec $cmd"
done

!/bin/bash or zsh?

bash