gistfile1.txt

render-template() {
	declare filename="$1"; shift
	local script k v
	for var in "$@"; do
		IFS='=' read k v <<< "$var"
		script="s/\$\$$k/${var##${k}=}/;$script"
	done
	cat "$filename" | sed "$script"
}

# usage: render-template /path/to/template foo=bar baz=qux
# replaces $$foo and $$baz in template to values bar and qux