module Concourse::Util

def erbify_file filename, working_directory: nil
  raise "ERROR: erbify_file: could not find file `#{filename}`" unless File.exist?(filename)
  template = File.read(filename)
  if working_directory.nil?
    working_directory = "." # so chdir is a no-op below
  else
    fqwd = File.expand_path(working_directory)
    $LOAD_PATH << fqwd unless $LOAD_PATH.include?(fqwd) # so "require" can load relative paths
  end
  Dir.chdir(working_directory) { ERB.new(template, nil, "%-").result(binding) }
end