Overview
A pipeline consists of a collection of stages, joined together by stage separators. Stages can be written in a variety of languages, and are either filters that process data records or device drivers (sources and sinks) that read data into or out of the pipeline. Unlike other implementations of pipeline programming, Hartmann's design has multiple streams in and out of each stage and can interconnect them non-sequentially. Unlike many programming languages, pipelines have a very small amount of notation, limited to stage separators (typically "|"), pipeline separators (typically ";" or "?"), and label separators (":"). Due to common usage, the diskread stage is also known as < and diskwrite as >, however all stages have names that are words in or make some sense in English.
A simple example that reads a disk file, separates records containing the string "Hello" from those that do not, and writes both sets of records to different disk files can be written as:
(end ;) < input.txt | A: locate /Hello/ | > found.txt ; A: | > notfound.txt
where the < stage reads the input disk file, the two > stages write the output disk files, and the locate stage separates the input stream into two output streams. locate's primary output (records containing Hello) is passed to the first > stage, and its secondary output (records not containing Hello) is passed through the A: connector to the second > stage. The ; divides the specification into 2 pipelines. The collection of pipelines is called a pipeline set.
Read more about this topic: Hartmann Pipeline