plumbing: [UNIX] n. Term used for {shell} code, so called because of the prevalence of `pipelines' that feed the output of one program to the input of another.

:plumbing: [UNIX] n. Term used for {shell} code, so called
because of the prevalence of `pipelines' that feed the output of
one program to the input of another. Under UNIX, user utilities
can often be implemented or at least prototyped by a suitable
collection of pipelines and temp-file grinding encapsulated in a
shell script; this is much less effort than writing C every time,
and the capability is considered one of UNIX's major winning
features. A few other OSs such as IBM's VM/CMS support similar
facilities. Esp. used in the construction `hairy plumbing'
(see {hairy}). "You can kluge together a basic spell-checker
out of `sort(1)', `comm(1)', and `tr(1)' with a
little plumbing." See also {tee}.
-- The AI Hackers Dictionary