It's doubtful that there is one piece of software that does anything non trivial that has bugs, even short command line programs. The best we can hope for is that bugs don't seem to cause too many problems.
> It's doubtful that there is one piece of software that does anything non trivial that has bugs, even short command line programs.
TeX and Metafont and other Knuth programs come pretty close.
There's also programs that have been proven correct. (And the proof systems themselves are usually fairly small and can have multiple independent implementations. Or at least the core of these systems that everything hinges on.)
