17 Principles of (Unix) Software Design

I came across this 1999-2003 e-book by Eric Raymond, on the Art of Unix Programming. It contains several relevant overviews of the basic principles behind the Unix philosophy, which are probably useful for anybody working in hardware, software, or other algoritmic design.

First up, is a great list of 17 design rules, explained in more detail in the original article:

  1. Rule of Modularity: Write simple parts connected by clean interfaces.
  2. Rule of Clarity: Clarity is better than cleverness.
  3. Rule of Composition: Design programs to be connected to other programs.
  4. Rule of Separation: Separate policy from mechanism; separate interfaces from engines.
  5. Rule of Simplicity: Design for simplicity; add complexity only where you must.
  6. Rule of Parsimony: Write a big program only when it is clear by demonstration that nothing else will do.
  7. Rule of Transparency: Design for visibility to make inspection and debugging easier.
  8. Rule of Robustness: Robustness is the child of transparency and simplicity.
  9. Rule of Representation: Fold knowledge into data so program logic can be stupid and robust.
  10. Rule of Least Surprise: In interface design, always do the least surprising thing.
  11. Rule of Silence: When a program has nothing surprising to say, it should say nothing.
  12. Rule of Repair: When you must fail, fail noisily and as soon as possible.
  13. Rule of Economy: Programmer time is expensive; conserve it in preference to machine time.
  14. Rule of Generation: Avoid hand-hacking; write programs to write programs when you can.
  15. Rule of Optimization: Prototype before polishing. Get it working before you optimize it.
  16. Rule of Diversity: Distrust all claims for “one true way”.
  17. Rule of Extensibility: Design for the future, because it will be here sooner than you think.

Moreover, the book contains a shortlist of some of the philosophical principles behind Unix (and software design in general): 

  • Everything that can be a source- and destination-independent filter should be one.
  • Data streams should if at all possible be textual (so they can be viewed and filtered with standard tools).
  • Database layouts and application protocols should if at all possible be textual (human-readable and human-editable).
  • Complex front ends (user interfaces) should be cleanly separated from complex back ends.
  • Whenever possible, prototype in an interpreted language before coding C.
  • Mixing languages is better than writing everything in one, if and only if using only that one is likely to overcomplicate the program.
  • Be generous in what you accept, rigorous in what you emit.
  • When filtering, never throw away information you don’t need to.
  • Small is beautiful. Write programs that do as little as is consistent with getting the job done.

If you want to read the real book, or if you just want to support the original author, you can buy the book here:

Let me know which of these and other rules and principles you apply in your daily programming/design job.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s