(Unix) 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 temporary 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 operating systems such as IBM's VM/CMS support similar facilities.
The tee utility is specifically designed for plumbing.
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Nearby terms: plug-in « PLUM « Plumber « plumbing » Plural EuLisp » PLUS » plus