code: function check_input(input, message) {
    if (!input) {
      error('\n  Error: ' + message);
      program.outputHelp(colors.red);
      process.exit(1);
    }
  }
docs: Checks that the given input is defined.  If it is defined, this is a no-op.  Else
  this prints the error message and halts the program with exit code 1.
  @param {input} input - The input to check
  @param {message} txt - The text to display if the check fails