Plumber (Plan 9)

Original text is located at "Plumbing and Other Utilities" (http://plan9.bell-labs.com/sys/doc/plumb.html)

Plumbing is a new mechanism for inter-process communication in Plan 9, specifically the passing of messages between interactive programs as part of the user interface. Although plumbing shares some properties with familiar notions such as cut and paste, it offers a more general data exchange mechanism without imposing a particular user interface.

The core of the plumbing system is a program called the plumber, which handles all messages and dispatches and reformats them according to configuration rules written in a special-purpose language. This approach allows the contents and context of a piece of data to define how it is handled. Unlike with drag and drop or cut and paste, the user doesn't need to deliver the data; the contents of a plumbing message, as interpreted by the plumbing rules, determine its destination.

The plumber has an unusual architecture: it is a language-driven file server. This design has distinct advantages. It makes plumbing easy to add to an existing, Unix-like command environment; it guarantees uniform handling of inter-application messages; it off-loads from those applications most of the work of extracting and dispatching messages; and it works transparently across a network.