Write programs that do one thing well and compose them through simple interfaces.
McIlroy's formulation. The composability is the payload: small tools with text interfaces combine in ways their authors never anticipated, which is why the shell outlived its designers' intentions.
In practice
- A tool that does nothing but sort lines is still being used inside workflows its author never imagined, forty years on.
- A team that builds four narrow services with clean interfaces gets combinations it never designed; one that builds a single configurable platform gets what it specified.
- Further reading
- Wikipedia
- Subject
- Technology & Software
- Essay
- Design rules that engineers pass down