lineswhich

Lineswhich is a hypothetical text-processing concept described as a lightweight utility and library for selecting lines from text data that satisfy a user-defined predicate. The name blends “lines” with the relative pronoun “which,” signaling line-by-line evaluation that defines the filter.

In its core model, lineswhich operates on a stream of lines, evaluating a predicate for each line and emitting only those that evaluate to true. Predicates can be expressed in a compact domain-specific language or via a host language callback, enabling simple conditions such as line length, content matches, or more complex logical combinations. The design emphasizes composability, streaming processing, and minimal memory use, making it suitable for logs, data preparation, and pipelines.

Usage typically involves a predicate specification and an input source. For example, lineswhich --predicate 'length(line) > 80' input.txt would output lines longer than 80 characters, while lineswhich --predicate '/ERROR|WARN/' input.log would filter lines containing error or warning indicators. Predicates may be inverted or combined with AND and OR, and the tool often supports reading from standard input to participate in Unix-style pipelines.

Implementation and ecosystem notes suggest that lineswhich can be delivered as a standalone executable or as a library in languages such as Python, JavaScript, or Go. It is designed to integrate with existing tooling, offering simple, line-oriented processing without requiring heavy scripting. In practice, lineswhich is discussed as a minimalist alternative to more feature-rich text processors in educational or prototyping contexts. There is no single standard, and variations exist across projects.

See also: grep, awk, sed.