title: Execute Shell Command Synchronously with Elixir/Erlang
body: <p>I want to execute a (slow) python script and I want my Elixir process to block until it's receives all the output from the script.</p>
  
  <p>Are either Elixir's System.cmd/3 or Erlang's os:cmd/1 guaranteed to be synchronous? If not, is there some other way to make a synchronous os call?</p>