# Program In Program (PIP)
safe_chdir('foo', 'Can't go to foo');
safe_system('foo --bar', 'foo didn\'t work');
safe_chdir('bar', 'bar is unreachable');

# Program In Data (PID)
@program = (
  [ chdir  => 'foo',       'Can't go to foo'   ],
  [ system => 'foo --bar', 'foo didn\'t work'  ],
  [ chdir  => 'bar',       'bar is unreachable' ],
);
run_program(\@program); # Hiding the dispatch and loop processing in a sub.